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Thread: A Treatise on Optimizing DSO Observation

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    Default A Treatise on Optimizing DSO Observation



    A Treatise on Optimizing DSO Observation

    Preface

    After writing A Treatise on Optimizing Planetary Views for the Planets forum, I was asked in the comments to
    write up something similar for DSO observation. What follows here is my best attempt to consolidate
    the information I've accumulated through this forum, other resources online, and my own experience,
    into a straightforward document describing how to get the most out of your telescope when trying to
    observe those elusive "faint fuzzies".

    You may find that there is some duplication of advice here and in the Planetary Observation
    document. However, I encourage you to read through the sections thoroughly, because there may be
    subtle changes from one to the other since observing planets is, in a lot of ways, very different
    from observing DSOs.

    I would like to emphasize that I am NOT a professional astronomer; I do NOT have a degree in
    astrophysics; I am NOT a seasoned veteran behind the scope. So while I will do my best to make sure
    that the topics I present are factually correct, I may make some mistakes! I encourage you to do
    your own research: don't take my word as the final say. If you do find factual errors, please note
    them in the comments and I'll work with a moderator to correct them in this post.

    Finally, try to keep an open mind. A lot of the information I present in this document is
    subjective -- it's stuff that might work great for me, but may not work so well for others. If you
    find that a tool or technique I've presented in this document are not effective, it doesn't mean
    you're "doing it wrong", it just means you've found a technique that doesn't suit you. Explore your
    options and come up with your own, personalized process for DSO observation that makes you
    happy.

    Thank you for reading, and a huge thanks to the hundreds of kind forum members who have helped me
    learn the ropes to such a degree that I feel confident writing this document.

    Introduction

    The first targets that tend to be observed by a budding amateur astronomer are the nearby planets.
    And for good reason: they're bright enough to be seen from even the brightest urban areas, they show
    incredible detail and color, and they are observed using high magnification, which feels appropriate
    for many new telescope owners, who feel like the ability to "zoom in" is the primary feature of
    their scope.

    But the fact is, there are only seven planets we can observe with amateur equipment (Mercury, Venus,
    Mars, Jupiter, Saturn, Uranus, Neptune), and of those, only three (Mars, Jupiter, Saturn) show any
    interesting detail on the surface. Not to say that planetary observation can get "boring" -- quite
    the opposite -- but it can get a bit repetitive, especially when there is only one
    "interesting" planet in a favorable viewing position.

    It's at this point that most astronomers will look to observe objects that lie outside our Solar
    System: so-called "Deep Space Objects" or "DSOs". There are literally billions of observable
    DSOs out there. OK, so the number that are readily observable visually in amateur equipment
    probably number in the thousands. But still -- the level of variety and sheer quantity of DSOs
    ensures that a sufficiently motivated amateur astronomer will never run out of new things to see.

    What I will try to do with this document is to guide you through the rich world of DSOs in such a
    way that you come away confident in your ability to observe them. I've broken the document into
    several sections that should, more or less, be in a reasonable order to ensure that you don't come
    across a topic in an earlier section that is explained in a later section.

    • DSO Classifications - What are the different types of DSOs? What are they, what properties do they have, and what do they look like in a typical amateur telescope?
    • Choosing the Right Telescope - There is no one telescope that "does it all". So what properties of each type of telescope contribute to effective observation of each kind of DSO?
    • Choosing the Right Eyepieces - Observing DSOs often requires subtle tweaks to magnification to get the best view. What properties should you look for in your eyepieces to get the best DSO views?
    • Choosing the Right Filters - Filters can help draw detail from otherwise featureless smudges, or even make some objects appear that were invisible before. What filters can be used to help observing, and how?
    • The Science of Scotopic Vision (Dark Adaptation) - "Hyper-tuning" your retina to maximize its sensitivity to light will make DSOs appear brighter and with more detail. This section goes over the physiology of the human eye and provides tips and suggestions for how to properly dark adapt as you observe.
    • Light Pollution and Atmospheric Conditions - What types of light pollution are there, and how do they impact what you see through the eyepiece? What types of atmospheric conditions are there, and how do they impact your view?
    • Selecting and Utilizing a Dark Sky Location - Selecting a suitable dark-sky site can be a daunting task, especially if you do not have an astronomy club nearby. This section will provide some guidance on how to choose a good (and safe) dark sky site.
    • Observing Techniques - Behaviors and tools you can use at the scope to see more than you thought possible.
    • DSO Catalogs, Star Charts, and Software Tools - An overview of the popular DSO catalogs, star charts, and software tools to help you with your observing.
    • Planning an Observing Session - Making the most of your time at the scope requires thorough planning. This section will provide some suggestions on how to create an effective observing plan.
    • Links and Resources - A dump of my browser bookmarks for your enjoyment

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    Default Re: A Treatise on Optimizing DSO Observation

    DSO Classifications

    Before diving into the details of the best way to observe DSOs, it's important to understand the
    differences in the types of DSOs. Each type has unique features that introduce different challenges
    when observing them.

    Double Stars

    The simplest type of DSO is the humble double (or triple, or more!) star. The main feature of a
    double star is that to the naked eye, it appears to be a single star, but is revealed to have
    multiple components when observed with optical aid. There are two types: star systems, where
    the stars actually orbit each other, and an optical double, where the stars only appear to be
    close to each other due to the line of sight.

    Double stars are a great way to test the limits of your telescope optics, as well as the seeing
    conditions at your site. Many are also brilliantly colored, sometimes with the components having
    strikingly different colorations. In general, there are two objectives when observing doubles: 1)
    to "split" the double [to resolve both components as separate points of light], and 2) to observe
    the difference in color and brightness of the pair.

    Many double stars can be split with a pair of 10x50 binoculars, but most require a telescope.
    Dawes' Limit defines the minimum apparent distance between two stars that are resolvable. This limit scales linearly with telescope aperture: in other words,
    splitting tighter doubles requires a larger aperture telescope.

    Some fine examples of double stars are Beta Cygni (Albireo), Epsilon Lyrae (the Double Double), and
    Alpha Geminorum (Castor).

    Open Clusters

    Open clusters are collections of stars that formed in the same stellar nursery at the same time, and
    move through the galaxy as a group. The component stars are loosely gravitationally bound to each
    other, and thus they are easily disrupted by passing objects. As a result, most open clusters have
    a lifetime of only a few hundred million years.

    Visually, open clusters appear as a dim smudge of light "behind" the surrounding smattering of
    stars, when viewed at low power, such as in a finder or binocular. At moderate magnification, open
    clusters are easily resolved into their component stars. Many open clusters are named after objects
    that the component stars appear to form. For example, M44, aka "the Beehive Cluster", looks to many
    observers like a beehive hanging from the branch of a tree. Open clusters can be fun to observe for
    the colors (NGC 4755, the "Jewel Box Cluster") and/or for the shapes the stars form (M11, the "Wild
    Duck Cluster"). My wife and I enjoy observing open clusters together and comparing what we "see" in
    the stars.

    Open clusters are found throughout the Milky Way and vary greatly in apparent size and brightness.
    One of the largest and brightest open clusters is M45, the Pleiades. It is nearly 2 degrees in
    diameter and has an apparent magnitude of 1.6. It is easily visible to the naked eye even under
    light polluted skies. At the other end of the spectrum, there are open clusters so dim and small
    that they can be difficult to pick out from the surrounding stars. An example of a small, dim
    cluster is M26, just 15' in diameter and magnitude 8.

    Globular Clusters

    Globular clusters are distinct from open clusters in that they are much more tightly packed, are
    tightly gravitationally bound, and tend to be very, very old. In fact, most globular clusters
    contain stars that were formed around the same time as our own galaxy! They orbit in the "halo" of
    the galaxy, far away from the core. Surprisingly little is known about how globular clusters form.

    You can see the difference between an open and a globular cluster immediately upon observing a glob.
    While open clusters are sparse and scattered, with well-defined space between each component,
    globular clusters are packed so tight that they appear as a spherical fuzzball, getting brighter
    toward the center. Their distance from us combined with the tight packing of their component stars
    makes resolving the individual stars in the cluster difficult without fairly large instruments.

    Unlike open clusters, most globular clusters appear pretty much the same. Careful observation can
    reveal unique features in each glob: this can be a fun aspect of observing them. Much like double
    star observation, observing globs can be a great way to test the limits of your optics and sky
    conditions, by seeing how "deep" into the cluster you are able to resolve individual stars. The
    largest globular clusters are around 30 arcminutes in diameter; most are quite a bit smaller than
    that.

    Some excellent examples of globular clusters are M13 (Great Hercules Cluster), M22 (one of the
    brightest globs in the sky), and Omega Centauri (the largest and brightest glob in the Milky Way).

    Emission & Reflection Nebulae

    In between all the billions of stars in our galaxy is an immense amount of gas and dust. In some
    regions, the gas and dust is clumped together more densely than in other areas. Often these dense
    clumps collapse in on themselves due to gravitation and form stars. These clumps of gas and dust
    are collectively called "nebulae" and fall into three visual categories:

    Dark Nebulae are clouds of dust that are invisible except that they happen to block the light
    from stars behind them from reaching us here on Earth. These nebulae appear like "ink blots"
    against rich star fields. Since they are not illuminated themselves, very little detail can be
    observed in them, except to trace their boundaries.

    Reflection Nebulae are glouds of gas and dust that become visible to us on Earth due to the
    light of a nearby star (or stars) reflecting off. These nebulae can be striking and beautiful, and
    some observers (particularly young ones) have occasionally reported being able to see colors in them
    through the eyepiece.

    Emission Nebulae are similar to reflection nebulae, except that instead of light reflecting
    off of them, they absorb energy from a nearby star. That absorbed energy causes gases in the nebula
    to become excited and radiate light on very specific spectral lines. This is an important
    distinction, because while reflection nebulae are visible across most or all of the spectrum,
    emission nebulae are often only emitting light on a few narrow slivers of the spectrum.

    Nebulae vary wildly in apparent dimensions. Large nebulae like M42 (Orion Nebula) and M8 (Lagoon
    Nebula) can be 2 degrees or more in apparent diameter, while other nebulae such as M17 (Swan Nebula)
    are as small as 10 arcminutes. Since their light is often quite faint and spread over a large area,
    they are very sensitive to the effects of light pollution.

    Planetary Nebulae

    The term "planetary nebula" is a bit of a misnomer. They are definitely not planets, but when
    William Herschel viewed them through his telescope, they appeared to resemble Uranus, which had
    recently been discovered. In reality, planetary nebulae are brightly lit shells of ionized gas
    being thrown off of a dying star. They come in a myriad of shapes and sizes, but all have a central
    star.

    Astrophotos of planetary nebulae can be incredibly beautiful. The ionized gases form lots of
    different colors, and the nebulae often demonstrate interesting symmetry. Visually, however, most
    planetaries do not give up much detail. All planetary nebulae appear in grayscale in a typical
    amateur telescope, and with few exceptions (M57 [Ring Nebula], M27 [Dumbbell Nebula], etc.) appear
    as a "fuzzy star" rather than the glorious detail seen in photos. However, this does not make them
    any less interesting to observe visually! Their similar appearance to surrounding stars can make
    them quite difficult to locate, and so definitely identifying them in your eyepiece can be a unique
    thrill even if you don't see anything spectacular in the object itself. Owners of very large
    telescopes may challenge themselves to visually observe the central star in a planetary nebula.

    While some planetary nebulae can be enormous in size (the Veil Nebula in Cygnus is a whopping three
    degrees in diameter), the vast majority are under 30 arcminutes, and at least half are under 60
    arcseconds.

    Some wonderful examples of planetary nebulae are M57 (Ring Nebula), M27 (Dumbbell Nebula),
    and M76 (Little Dumbbell Nebula). All three of these planetary nebulae will exhibit easily
    discernable shapes in the eyepiece of a typical amateur instrument.

    Galaxies

    When observing deep space objects, you literally cannot get any further into "deep space" than by
    observing galaxies. While the objects in our Milky Way galaxy are at most about 100,000 light years
    distant, even the nearest galaxies are millions of light years away! The most distant
    galaxies we can see with typical amateur equipment can be tens of millions of light years away. For
    example, M104 (the Sombrero Galaxy) is easily visible in a 6" scope and is nearly 30 million light
    years distant.

    Simply grasping the reality that you are looking at a collection of billions of stars,
    collecting photons that left their parent stars tens of millions of years ago, is truly an
    awe-inspiring moment in any astronomer's career, professional or otherwise.

    Galaxies can vary in apparent size from very large (M31 has an apparent diameter of over 100
    arcminutes) to very small (M60 is just 2 arcminutes across).

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    Default Re: A Treatise on Optimizing DSO Observation

    Choosing the Right Telescope

    Luckily, choosing the right telescope for DSO observation is pretty easy. There are really
    just three things to consider, in this order: aperture, optical design, and mount.

    DSOs are very faint, so to see them, you need to amplify the light they emit to levels where your
    retina can register the signal. There's only one way to do this: bigger optics. To observe the
    entire Messier catalog, you can get by with a 4" scope, but really you'll have better luck and a
    more enjoyable experience with a 6" scope or larger. Commercially manufactured amateur telescopes
    get as large as 16", and those with really deep pockets can get custom scopes 32" and even larger!

    Telescope

    So clearly you want a big scope. But bigger is not always better, especially when it comes to
    factors like portability and ease of use. There are three basic types of telescopes to consider:
    refractors, reflectors, and catadioptric.

    Refractors are what people tend to think of when somebody mentions a telescope. It's got a
    lens up in the front, and you look through it from the back. Refractors have no central
    obstruction, and so they deliver pinpoint-sharp views of stars. That means open clusters and
    globular clusters really come alive in a refractor. However, refractors with large apertures are
    often prohibitively expensive for most amateurs, and they get even more expensive when you go to
    apochromatic models that feature full color correction. They also require a big heavy-duty mount
    due to their size and weight. Thus, they tend to be somewhat difficult to move around.

    Reflectors use a mirror to focus light rather than a lens. Because the focal point
    is thus in front of the mirror, a second, angled mirror is required to direct the light to the
    side of the tube, near the front of the telescope. This design is called a "Newtonian Reflector"
    after its inventor, Sir Isaac Newton. Reflectors have a key advantage over refractors in that
    it is much less expensive to figure a large mirror to high precision than a large lens. So
    for a given aperture, a reflector is going to be MUCH less expensive than a refractor. Reflectors
    also have the advantage that they focus all frequencies of light to the same place, so they
    do not suffer from chromatic aberration like refractors do. The nature of their design means
    that in larger apertures they can usually be broken down into several separate components, making
    them easy to transport to your favorite dark sky site.

    However, there are some downsides. First, all Newtonian reflectors suffer from an aberration known
    as coma. This aberration appears in the eyepiece as "comet-shaped" stars at the edges of the
    field. The amount of coma is proportional to the distance from the center of the field. Scopes
    with fast focal ratios (f/6 and lower) tend to show coma halfway out from the center of the field,
    while slower scopes (f/8 and higher) can keep a sharp image across as much as 90% of the field.
    Coma can be corrected in faster scopes using a device such as the Televue Paracorr. The nature of
    Newtonian reflectors (big aperture, eyepiece at the top of the tube) means that design
    considerations tend to make them have relatively fast focal ratios. At 10" and larger, f/4 and f/5
    is very common. They also have a central obstruction from the secondary mirror, which can reduce
    contrast and make stars less sharp. But you probably don't need to worry about this so much;
    both of these can be counteracted with more aperture. Finally, newtonian reflectors require
    frequent collimation to keep the primary mirror, secondary mirror, and focuser drawtube all
    precisely aligned, otherwise the image suffers.

    Catadioptric telescopes use both lenses and mirrors and feature "folded" optics. The basic
    design takes advantage of the benefits of reflectors (large aperture, lack of chromatic aberration),
    and uses some extra elements (coma correcting front lens, convex secondary mirror) to create a
    compact, coma-free, long focal length telescope. While not available in as large of apertures as
    Newtonian reflectors, they do come in up to 14" models that are affordable by many amateurs. They
    have many advantages: compact size, light weight, and lack of coma and chromatic aberration.
    However, they tend to have narrower fields of view than equivalent aperture refractors and
    reflectors, and they take a lot longer to come to thermal equilibrium. They also require
    collimation much like a reflector (but not as often). They are also more expensive for a given
    aperture than a reflector.


    Mount

    Of the three major types of telescopes, there are many different ways each can be mounted. How
    to choose? There are three different types of mounts: german equatorial, dobsonian, and fork.

    German equatorial mounts align one of their rotational axes with the Earth's axis so that
    it is possible to track objects by simply driving one axis with a clock drive. Most models you
    will see these days will have drive motors on both axes as well as a hand controller that provides
    GOTO capability. One advantage of equatorial mounts is that they are easy to set up: just aim
    the RA axis north, set the latitude, and start observing. If you choose to use GOTO, the process
    is the same, but you also have to go through an alignment process. Equatorial mounts are also
    the ideal platform for astrophotography, if you choose to get into that in the future. There
    are some downsides to an equatorial mount, though. Their load carrying capacity is fairly small
    for the price, and they are heavy to lug around, mostly due to the big counterweights they require.

    Dobsonian mounts are extremely simple but sturdy mounts pioneered by John Dobson. His idea
    was to bring astronomy to the masses, and he saw the complex and expensive german equatorial mount
    as a detractor of this goal. He designed a simple but sturdy telescope mount designed to carry
    Newtonian reflectors. The mount consists of a ground board that acts like a lazy susan,
    allowing the telescope to rotate in azimuth (left to right). On the ground board sits a rocker
    box
    , sort of like a "fork" that holds the telescope from its balance point near the center,
    and allows the telescope to rotate in altitude (up and down). That's it -- so simple that pretty
    much anybody with a sheet of plywood and some basic hardware could build one, and scalable up to
    huge (or tiny) apertures. The simplicity of the mount also translates to simplicity of use. There
    is no aligning to do: just level the ground board, drop the scope into the rocker box, and start
    observing. No need to deal with batteries, clock drives, or celestial coordinates. The scope
    is aimed using simple left-right up-down movements. The downsides, though, are that the alt-az
    motion makes tracking objects (especially at high power) over a long period of time more difficult.
    They are also unable to locate targets for you (though there are models that include axis encoders
    and a computer locator, and others that even have drive motors and GOTO capability and tracking,
    but these features can quickly run up the price).

    Fork mounts can be half-forks (holds the scope on one side) or full-forks (holds the
    scope on both sides). Fork mounts are most common with catadioptric telescopes. They can
    carry large apertures (though pratically speaking, 14-16" is the largest you'll find for sale),
    and most come with drive motors and GOTO capability standard. They can also be "wedge" mounted,
    which aligns the azimuth axis with the Earth's rotational axis so they can gain the advantages
    of a german equatorial mount (but without the counterweights). In all, forks can be a great
    compromise between the simplicity and low cost of a dobsonian mount and the complexity, weight,
    and high price of an equatorial mount. However, they do not track quite as well as equatorial
    mounts, and they can't carry as large of apertures as dobsonian mounts. They really only come
    with catadioptric scopes mounted, so you won't find them with big newtonian scopes attached.
    Some smaller refractors you can find mounted on half-forks, though. But if you want large
    aperture and a fast focal ratio, you probably won't find it on a fork.


    Best Buys

    So what's the "best" telescope for DSO observation? That's an awfully tough question to answer.
    And so really I won't even try. What I will say is that when it comes to a "best buy" for a
    beginner, you really can't go wrong with a 6-10" dobsonian, such as the Orion XT6, XT8, or XT10. If
    you can afford the "i" series with the computer locator, that's a great upgrade that can make it a
    lot easier to find objects, especially under light-polluted skies. If you start getting into a
    dobsonian with drive motors and GOTO, however, you start bumping into pricing that competes with
    other types of telescopes, and then it gets really difficult (and very personal) to select the
    "right" scope for you.

    Just remember that if you're on the fence between two scopes, chances are the one with larger
    aperture is the one you probably should get, provided you will be comfortable actually pulling it
    out of the closet and setting it up. A scope that sits in the closet and doesn't get used is the
    worst scope of all!

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    C10-N/C14+Losmandy G11; Portaball 12.5"; NexStar 6SE; Meade ETX125; Stellarvue F80
    Meade HD-60 9mm, 6.5mm; 56mm; University Optics Orthoscopic 12.5mm, 9mm, 7mm, 5mm;
    ES 70° 15mm, 20mm; ES 82° 30mm, 18mm; ES 100° 9mm; Baader Hyperion 24mm; TV Nagler T6 13mm
    William Optics Binoviewer; GSO 2" 2x ED barlow; 5x APO barlow, Parks 2.5x APO barlow
    Filters: Orion Ultrablock, Thousand Oaks OIII

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    Default Re: A Treatise on Optimizing DSO Observation

    Choosing the Right Eyepieces

    Once you have decided on your telescope (or if you have been given one as a gift), the next
    thing you need to do is to obtain a set of eyepieces that will maximize your ability to
    observe DSOs with it. Choosing the right eyepieces requires no prior knowledge about the
    design of the telescope, its focal length, or its aperture. All that you need to know
    is the focal ratio (found by dividing the focal length by the aperture). A 16" f/5
    dobsonian will have the same set of recommended eyepieces as a 4" f/5 short tube refractor,
    since their focal ratios are the same.

    First, let's talk about the exit pupil, and how it relates to magnification,
    image brightness, and optical clarity. The exit pupil is the size of the shaft of light
    coming out of the eyepiece. Larger exit pupils equate to lower magnification, and smaller
    exit pupils equate to higher magnification. You can think of the exit pupil in this way:
    A telescope's job is to take a bunch of parallel rays of light coming from a target, such
    as a star, catch them, and compress them down into a bundle of rays that will fit into
    your eye. By scrunching them together, you land more photons from the target on each
    cell in your retina, and thus you are able to see a brighter target than before. The
    size of the exit pupil is the size of that exiting bundle of light rays.

    The exit pupil size can be calculated with this simple formula:

    exit pupil = focal length of eyepiece / focal ratio of telescope

    So for example, a 15mm eyepiece used in a f/5 newtonian reflector would result in a 15/5=3mm
    exit pupil, while that same eyepiece used in a f/15 maksutov cassegrain scope would result in
    a 15/1=1mm exit pupil. Notice that the exit pupil size scales only with the focal ratio of
    the telescope (assuming the eyepiece stays the same). A 15mm eyepiece in a 5" f/5 reflector
    gives a 3mm exit pupil, while that same eyepiece in a monster 24" f/5 Obsession would still
    give a 3mm exit pupil.

    When looking at eyepieces, most people have a tendency to look at the absolute magnification
    first when deciding what to buy. They know that the magnification is focal length of the
    telescope divided by the focal length of the eyepiece, and then tend to look at the specs
    for the telescope to see which magnifications are "in range". Trouble is, looking at absolute
    magnifications doesn't take into account things like image brightness, visual acuity, and
    human pupil sizes. Using the exit pupil instead of absolute magnification to determine
    the eyepiece focal lengths to use does take these into account -- the rest of the factors
    (field of view, magnification) will fall into place automatically.

    Here is the range of useful exit pupils:

    • 5-7mm - minimum magnification. The human pupil, when dark adapted, can get as large as 7mm (for young observers under very dark skies). As you get older, your pupils can't expand as large, and if you aren't under pristine dark skies, the ambient light may cause your pupils to not fully dilate. So 7mm is generally considered to be the maximum exit pupil size, but in reality this could be anywhere from 5-7mm, depending on your age and other factors. Also consider that your eye has a lens it it as well, that is likely not perfectly figured. Spreading the light over a larger area of your cornea can cause aberrations like astigmatism to be more noticeable than with smaller exit pupils, which only use a smaller part of your eye lens. Reference: Telescope Equations: Minimum Magnification and Telescope Equations: Surface Brightness
    • 2mm - optimum magnification. As magnification increases, the light for a given area in your field of view gets spread over more of your retina. Thus, increasing magnification dims stuff in the field (except for stars, which stay as points, and thus maintain their brightness). Galaxies and nebulae get dimmer as you increase magnification, at the same rate as the background skyglow. So how can there be an "optimal" magnification? Well, it turns out that the human eye is able to detect faint objects better if they're larger in size. But as things get larger, they get dimmer. It turns out that a 2mm exit pupil is the ideal balance of image scale and brightness to detect faint objects. Reference: Telescope Equations: Surface Brightness
    • 1mm - maximum magnification. As the exit pupil shrinks below 1mm in size, the image begins to dim noticeably, and no new detail can be seen. All you are doing when using an exit pupil smaller than 1mm is magnifying the details that were already there at 1mm; not bringing out new details. Furthermore, beyond a 1mm exit pupil, stars stop being point sources and begin expanding into Airy patterns, which means they begin to be subject to the effects of dimming with increased magnification. In other words, faint stars visible with a 1mm exit pupil may not be visible anymore with a .75mm or .5mm exit pupil. Reference: Telescope Equations: Maximum Magnification


    Keep in mind when choosing eyepieces that you probably want at least one eyepiece for each of these
    three exit pupils, and probably a fourth that fills in the middle between your 5-7mm exit pupil and
    the 2mm exit pupil.

    So what size exit pupils are ideal for which types of objects?

    • Double Stars - 0.5-1mm exit pupil - when trying to split double stars, magnification is the name of the game. Sure, magnifying beyond a 1mm exit pupil makes the Airy pattern visible, but when splitting tight doubles, often what you're actually looking for is a "lumpy" Airy pattern. When observing doubles that have a dim partner to a bright primary, super-high magnification can cause the primary to dim (due to it becoming an extended object), which can help detection of the secondary. Experiment, of course, but you will probably find that splitting tight doubles works best with a very small exit pupil.
    • Globular Clusters - 1mm-2mm exit pupil - Globular clusters are collections of stars, and so increased magnification (up to a 1mm exit pupil) will dim the background sky and make more and fainter stars visible. Globs tend to be small, with dense cores. Increasing magnification can help you to resolve more stars at the center of the glob.
    • Open Clusters - 2mm-7mm exit pupil - Open clusters tend to be fairly expansive in size, and thus tend to require lower magnification to fit the entire cluster in the field. In general, you should try to use enough magnification to just fit the whole cluster comfortably in the field. The increased magnification will make more stars in the cluster visible, but it has to be balanced with the ability to actually fit the cluster in your field of view. An eyepiece with a large AFOV can help you to fit larger clusters in the field without giving up the magnification that makes the fainter members visible.
    • Reflection and Emission Nebulae - 2mm-7mm exit pupil - These, like open clusters, tend to be fairly large, and so a lower magnification may be required to fit them in the field. However, unlike star clusters, increasing magnification will not make nebulae easier to see. As magnification increases, they will get dimmer at the same rate as the background sky, and so you do not increase contrast. So just try to fit the object comfortably in the field. You may find that more magnification will reveal some subtle detail, and lower magnifications will frame the nebula nicely among the stars.
    • Planetary Nebulae - 1mm exit pupil - these are tiny, so high magnification is required to see any structure in them, but magnification higher than a 1mm exit pupil will make the nebula unnecessarily fuzzy and difficult to observe.
    • Galaxies - 2mm exit pupil - galaxies are among the faintest objects you'll ever try to observe, so it's crucial to stack as much in your favor as possible. A 2mm exit pupil will give you the best chance of picking the fuzzy patch out of the background sky. Some larger galaxies may not fit in the field with a 2mm exit pupil: in those cases you will need to go to a lower magnification (larger exit pupil).


    All right -- at this point you should have a good idea of the eyepiece focal lengths that you want,
    based on the exit pupils noted above. For example, if you have an 8" f/6 dobsonian, your "optimal"
    2mm exit pupil would be achieved with a 2 * 6 = 12mm eyepiece. However, if you have a 10" f/4.7
    dobsonian, that same exit pupil would be achieved with a 2 * 4.7 = 9.4mm eyepiece.

    So what else should you consider other than the focal length of the eyepiece?

    Apparent Field of View (AFOV)

    The AFOV is the apparent size of the field that you see through the eyepiece. A narrow AFOV makes
    it feel like you are observing through a wrapping paper tube, while a wide AFOV can extend the field
    well into your peripheral vision, giving you a "spacewalk" experience.

    When searching for eyepieces for observing DSOs, generally wider AFOVs are better. Why? Well, say
    you are purchasing an eyepiece for the 2mm exit pupil slot in your lineup. The focal length of the
    eypiece you want is fixed, and thus so will the magnification when used in your scope. To ensure you
    maximize the amount of sky you'll be able to fit in the field at that particular exit pupil, a wider
    AFOV will draw in more sky.

    However, some observers find ultra-wide AFOVs to be uncomfortable, as you sometimes have to
    physically move your eye around in order to see all the way out to the field stop. Also, eyepieces
    with very wide AFOVs tend to have limited eye relief, and so if you wear glasses at the scope (only
    necessary if you have bad astigmatism), you might need to compromise a large AFOV for an eyepiece
    with long eye relief.

    The most popular wide AFOV eyepieces today have an 82 degree AFOV. Other common widefield eyepieces
    are also available with 68/70 degree and 100 degree apparent fields. Explore Scientific even has a
    9mm eyepiece with a whopping 120 degree AFOV.

    Eye Relief

    Eye relief is the distance that your eye must be positioned away from the eye lens in the eyepiece in
    order to see the whole field, and to get the best performance from the eyepiece per the designer's
    intended specifications.

    Eye relief of 5mm is extremely tight, 10mm is bearable, 15mm is comfortable, and 20mm is long enough
    for comfortable use with eyeglasses on.

    Most premium eyepieces list the eye relief along with the other specifications such as focal length
    and AFOV. However, many simple eyepieces (Plossl, Orthoscopic, Monocentric, etc.) may not list eye
    relief. In that case, the eye relief is often close to the focal length of the eyepiece. For example,
    a 10mm Plossl generally has ~10mm eye relief.

    Spherical Correction

    The eyepiece's job is to magnify the image created by the telescope at its focal plane and present
    it to your eye. Trouble is, the focal "plane" created by the telescope isn't actually flat.
    Rather, it is curved. The faster the telescope (the smaller the f/ ratio), the more curved the
    focal plane is. Simple eyepieces like Plossls are not capable of properly handling highly curved
    focal planes. The result is a visual aberration called spherical aberration. Visually, this
    makes stars look "bloated" or out of focus at the edges of the field, while the center of the field
    is in focus. Sometimes you can even tweak the focus knob and get the edges to snap into focus (but
    take the center of the field out of focus). When you hear somebody describing an eyepiece as being
    "soft at the edges", this is probably the aberration they are referring to. The opposite would be
    if the stars are "tack-sharp" from edge to edge.

    If the telescope you are using has a slow focal ratio (f/8 and up), you can get away with cheaper,
    simpler eyepieces like Plossls. If your scope is fast (f/6 and down), you should look for eyepieces
    that are well corrected. The correction is provided through the use of extra lens elements.
    Eyepieces with six or more lenses tend to have good spherical correction (though this is not a
    hard-and-fast rule). Beware that more lenses doesn't necessarily equate to a better view; it's just
    a starting point when trying to determine whether an eyepiece will work well in a fast telescope. A
    six-element Celestron XCel-LX will have better spherical correction than a 5-element Super Plossl,
    and much better correction than a standard 4-element Plossl. As a bonus, well-corrected eyepieces
    tend to have wider AFOVs. However, more lens elements means the eyepiece is more expensive, and the
    extra air-to-glass surfaces means more potential for internal reflections and ghosting (which
    negatively impacts contrast, especially on bright subjects). Additionally, each lens element can
    only transmit ~95-98% of the light encountering it, so more lens elements means less light is
    actually making it to your eye. When trying to observe something that is juuuuuust at the
    edge of observability, a high quality, simple eyepiece with few lens elements might give you just
    enough boost to see it.

    Keep in mind, however, that quality eyepiece manufacturers have virtually perfected multi-element
    designs such that they give very good contrast and light transmission -- don't automatically
    assume that a simple eyepiece is "better" than a complex one just because of this one metric.

    Coatings and build quality

    Your eyepieces are fully half of your telescope's optical system. A poorly built eyepiece can make
    the view through a $15,000 telescope look like a $50 toy, while a well built eyepiece will always
    bring out the best of any telescope. Not to mention that you can keep your eyepieces and use them
    with your next, better telescope, so why not buy the best you can afford, so you only have to buy
    once?

    The two factors to consider when looking at build quality are the physical characteristics and the
    coatings. Companies like Baader Planetarium and Televue use ultra-high-tech (and expensive)
    multi-coatings on every lens surface to reduce glare and improve light transmission. Lower-priced
    clones may have the same lens design, but may not have the same sophisticated coatings. That's not
    to say that the eyepieces made by Meade, Celestron, GSO, Orion, and others aren't good quality -- in
    fact, often these eyepieces are a fantastic bang for the buck, giving you 80-90% of the quality at
    half (or less) the price of the premium ones.

    When looking at the physical characteristics, look for features like soft rubber folding eyeguards,
    twist-up eyecups, anodized components, blackened lens edges, and waterproofing. No eyepiece will
    have everything, but keep in mind that when comparing two eyepieces that optically may be identical,
    sometimes the extra cost is worth it for the "perks" you get with things like a nice twist-up eyecup.

    Barrel diameter (2" vs 1.25")

    A common misconception many beginners have is that 2" eyepieces are "better" than 1.25" eyepieces.
    After all, they tend to be more expensive than their 1.25" cousins, and their massive size suggests
    that they must be doing something better than a comparatively puny 1.25" eyepiece.

    Myth: 2" eyepieces collect more light (or provide a brighter image) than a 1.25" eyepiece.

    Reality: The brightness of the view you get through the eyepiece is strictly based on the
    size of the exit pupil, and the clear aperture of the scope. A faster scope won't give you a
    brighter image in the eyepiece than a slow scope (assuming the same exit pupil size and aperture).
    Similarly, a larger eyepiece won't make the image any brighter than a smaller one, assuming the
    exit pupil stays the same.

    As the focal length of an eyepiece increases, the field stop (the circle at the focal plane where
    the eyepiece lets light in) gets larger. The AFOV of the eyepiece design also has an effect on the
    field stop size -- it sort of acts like a "multiplier". So a 32mm Plossl (with a 50 degree AFOV)
    has a 29mm diameter field stop (1.14 inches) -- thus it just barely fits inside a 1.25" eyepiece
    barrel (with .1" to spare for the barrel material). Meanwhile, a 31mm Nagler with an 82 degree AFOV
    has a 44.4mm diameter field stop (1.75") that effectively maxes out a 2" eyepiece barrel.

    Myth: 2" eyepieces have better optics than 1.25" eyepieces

    Reality: Eyepiece manufacturers ship eyepieces in a barrel that makes the most sense for
    the optical design. Long focal length, wide-AFOV eyepieces require field lenses larger than
    1.25" and thus must be shipped in a 2" barrel. For example, the Explore Scientific 82 degree
    series is 1.25" in the models up to and including the 14mm. The 18mm and up ship in 2" barrels.
    The 18mm and 14mm are similar focal lengths -- is the 18mm optically superior to the 14mm? No.
    It's just that the field lens is larger than what fits in a 1.25" barrel when you go beyond 14mm
    with Explore Scientific's design.

    In short, choose your eyepieces based on the factors noted above -- the barrel diameter will follow.
    xphile, gregl, Philip F and 13 others like this.

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    Default Re: A Treatise on Optimizing DSO Observation

    Choosing the Right Filters

    With names like "Light Pollution Reducing" and "Ultra High Contrast", it's often hard to resist the
    allure of filters for DSO viewing. But unfortunately, the marketing material that comes with each
    filter tends to hype up the benefits without also talking about the downsides.

    The first, and most important thing to know about filters is that they cannot make the object
    you are observing any brighter. In fact, all filters actually make the image dimmer
    in the eyepiece, because they block portions of the visible spectrum. However, what filters
    can do is to improve contrast by dimming the background, but not dimming the object
    by the same amount, thus increasing the difference and brightness (which is contrast).

    Before we dive in, a quick discussion about what we are actually seeing through the eyepiece.
    The light arriving at the primary mirror or objective lens of your telescope comes from a
    variety of sources: the stars in the field, reflections off of dust clouds, and the dull
    glow from ionized gas. In addition, there is light arriving from local sources, namely
    skyglow (the light that the atmosphere naturally creates on its own), and terrestrial light
    (street lamps, headlights, etc.) reflecting off of dust and water droplets suspended in the
    air.

    Every source of visible light is made up of a set of frequencies, or wavelengths, of light.
    You've seen the spectrum of light refracted through a prism before; each color in the spectrum
    is a different wavelength. Shorter wavelengths are to the violet end of the spectrum, while
    longer wavelengths are to the red end of the spectrum.

    What is interesting about this is that some light sources emit in very specific parts of the
    spectrum. For example, high-pressure sodium vapor floodlights emit over 90% of their light in a
    very narrow part of the spectrum, around 590nm. Mercury vapor floodlights emit most of their
    light in three narrow lines: 435nm, 546nm, and 578nm. Some astronomical objects (emission
    nebulae, planetary nebulae) also emit their light in a narrow part of the spectrum.

    And this is where filters come in. There are four basic types of filters:

    • Broadband filters selectively block a few key lines of the spectrum, such as those emitted by mercury vapor and sodium vapor floodlights. This can help to darken the background by eliminating some of the light generated by terrestrial sources, while still allowing most other light to get through. Broadband filters are usually marketed as "light pollution reduction" -- Lumicon Deep Sky, Orion Sky Glow, Thousand Oaks LP-1.
    • Narrowband filters are the inverse of a broadband filter. While broadband filters selectively block certain wavelengths of light, narrowband filters selectively pass certain wavelengths. Generally, narrowband filters pass the range of 484nm to 506nm, and block everything else. A large class of astronomical objects emit a substantial portion of their light in this segment of the spectrum (the two OIII lines and the H-Beta line) and so these filters can greatly improve visual contrast on these objects while leaving the background inky black. Common narrowband filters are Lumicon UHC, Orion Ultrablock, and Thousand Oaks LP-2.
    • Line filters are similar to narrowband filters, except that they only pass a single wavelength of light, usually associated with a type of glowing gas. Typical line filters used in astronomy isolate the OIII, H-beta, and H-alpha lines. Lumicon, Orion, GSO, and many others make line filters for OIII, H-Beta, and H-alpha.
    • Color filters are sort of like narrowband filters, only they isolate a very broad segment of the spectrum associated with that color. They are not generally useful for observing DSOs. One color filter of note, however, is the "CCD Green" filter. Interestingly, a great deal of astronomical objects emit the majority of their light in the green portion of the spectrum (which contains, among other lines, OIII and H-beta), so a green filter can work somewhat like a broadband filter.


    So should you buy a filter? And if so, what kind? Dave Knisely does a much better job than I could
    describing it, so I'll just link you to his fantastic post: » Some Available Light Pollution And Narrow-Band Filters The Prairie Astronomy Club

    Additionally, keep in mind that all filters are not created equal. In particular, some cheaper
    filters have lower light transmission, and some even have bandpasses in the wrong place, making them
    practically useless! Be sure you check reviews and, if possible, independent spectroscopic analysis
    of any filter you plan to purchase. For example, here is an independent spectroscopic review of
    some assorted OIII and narrowband filters: Forbidden Lines: Mini [OIII] Filter Shootout - Review

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    Default Re: A Treatise on Optimizing DSO Observation

    The Science of Scotopic Vision (Dark Adaptation)

    You have probably heard about "dark adaptation" and how important it is for observing DSOs. But
    what does it mean to be dark adapted? What are the physiological changes that happen, and what
    triggers those changes? What are the effects of dark-adapted (scotopic) vision?

    Physiology of the Human Eye

    The human eye operates by focusing light entering through the cornea, through the pupil, and then
    through the lens, onto the retina, which has special light-sensitive cells on it. There are two
    kinds of these cells: rods and cones.

    Cones are sensitive to color, and are clustered primarily in the center of the retina. They require
    a lot of light to fire, but when they are operating, you can see with a great deal of clarity and
    high resolution. This is because cones are packed very tightly together, so small features can be
    resolved easily. When there is enough light for you to see in color, you are said to be using
    "photopic" vision.

    Rods are only able to sense grayscale, and are distributed more across the edges of the retina.
    They require much less light to fire, and thus are used for seeing in low-light conditions.
    However, since they're more spread out, you don't have the same visual acuity (resolution) in low
    light as you do in normal light. When you are using your rods to see, you are said to be using
    "scotopic" vision.

    One important thing to note about your rods is that the process they use to detect light is through
    a chemical reaction. There is a chemical called rhodopsin that slowly builds up in your
    rods. The presence of rhodopsin enhances your rods' sensitivity to light by as much as 1000x, but
    it takes some time for the rhodopsin to build up. Your rods have an auto-protection feature built
    in, though. If bright light enters the eye, the rhodopsin "bleaches" out of the rods, eliminating
    the extra light sensitivity. This allows us to not be blinded during the day, while also being able
    to see at night.

    For more on the optical theory of observation, see this wonderful site: http://starizona.com/acb/basics/observing_theory.aspx

    Our goal, then, when dark-adapting, is to maximize the amount of rhodopsin built up in our rods,
    and keep it built up, to ensure that we are able to see the faintest amount of light possible
    .

    Dark adaptation best practices

    • Be patient. It takes a half hour or more to become fully dark adapted. If you head out from a brightly lit house to your backyard, plunk down in front of the scope, and try to observe a faint fuzzy, chances are you're going to be disappointed. You need to give yourself plenty of time to get properly dark adapted.
    • Eliminate local bright lights. Remember the thing about the rhodopsin bleaching out? Any bright light can do this -- a street lamp, light from a room in the house spilling out into your observing area, or your cell phone/tablet/laptop display. Do everything you can to eliminate these localized sources of bright light, to ensure you get fully dark adapted.
    • If you need extra light, use a dim, red light. The most important thing is that it be dim. The color actually doesn't matter, but convention dictates that it be red, and you really don't want (or need) to get into an argument with another observer regarding the color of your light. The light you use should be just bright enough to perform a task (like reading a star chart) but no brighter. Did I mention it should be DIM? Because yeah, it should be a DIM light.
    • Don't use backlit devices (cell phones, tablets, laptops) while observing DSOs. Even in "night vision" mode, the screen is still WAY too bright to preserve your dark adaptation. You might be OK with a few layers of red rubylith laid over the screen *and* night vision mode, but is it really worth it at that point?
    • Use paper star charts. Sky & Telescope's Pocket Sky Atlas is a fantastic chart to use at the scope. A dim red light will very easily illuminate a paper chart without damaging your scotopic vision. There's nothing wrong with using technology to help you plan what you want to observe, but once you have the plan made, keep the electronics in your case, powered down. Your eyes will thank you.
    • Enhance your dark sensitivity at the eyepiece by sitting down. Sitting while at the eyepiece means your eye sits still, which means the image of your target stays put over the same rods for an extended period of time. To a small degree, your rods act like the pixels on a CCD chip -- staring for a few seconds can cause some rudimentary "stacking" behavior to happen, increasing your ability to see.
    • Use averted vision. The center of your visual field is dominated by cones, which are useless in low light. Your rods are more prevalent in your peripheral vision. When trying to see detail in a faint fuzzy, try looking off to the side of it. You will probably notice it get brighter and more detailed when it's not in the very center of your focus.
    • Breathe deeply. I've heard that breathing deeply increases the amount of oxygen in your bloodstream (and thus your retinas), which enhances your rods' sensitivity. Personally I haven't noticed a difference, but some do, so you might as well give it a try for yourself.


    A note about pupil size

    As mentioned in the section above about choosing an eyepiece, the human pupil can open up as wide as
    ~7mm when fully dark adapted. But as you get older, your pupil begins to lose some of its
    flexibility and can't open as wide. Seniors may find that their pupils may only open to 4mm or even
    less when dark adapted. Also, bright surroundings (such as those commonly found under heavily light
    polluted skies) can prevent the pupil from fully expanding. Keep this in mind when choosing a
    low-power eyepiece: if the exit pupil of the telescope+eyepiece is wider than your pupil has
    expanded, then light will fall onto your iris rather than enter the eye. The result is lost light,
    and you effectively stop down your telescope to a smaller size. If you do a lot of observing from
    light polluted areas, or if you are getting older, then you might consider sizing your wide-field
    eyepiece with an exit pupil closer to 4mm or 5mm rather than the accepted 'default' of 7mm.
    Last edited by skaven; 01-06-2013 at 12:10 AM.
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    Default Re: A Treatise on Optimizing DSO Observation

    Light Pollution and Atmospheric Conditions

    The bane of every DSO observer (other than clouds) is light pollution. That yellowish or pinkish
    haze that hangs in the air and turns otherwise spectacular DSOs into boring puffballs set on a gray
    background. But what is light pollution? And are there other ways that the atmosphere can affect
    your views?

    Light Pollution

    Light pollution comes in two flavors: local and regional.

    Local light pollution consists of light sources near your observing site that interfere with your
    proper dark adaptation. Common examples are street lights, porch lights, and even car headlights
    (if your observing location is near a roadway). It is important to note that local light pollution
    does not directly impact your view through the eyepiece. What it does do, though, is to
    make it harder (or impossible) to properly dark adapt. It can also cause glare and distracting
    reflections in the eyepiece.

    Regional (or "atmospheric"? I'm just winging it here with these names) light pollution is caused
    by a general presense of lights in the area. You need a lot of lights nearby for them to start
    forming a "light dome". Regional light pollution appears as a noticeable glow in the sky. It
    makes passing clouds visible from the bottom. Often it can be so bright that you can clearly see
    your surroundings and are unable to properly dark adapt. But most importantly, it appears in
    the eyepiece as a contrast-robbing background glow that obscures the objects you're trying to
    observe.

    Keep in mind that a given location might have one, but not the other, kind of light pollution.
    The best spots are those that have neither. A parking lot in the middle of the desert might have a
    bright light illuminating it, but the overall sky is pitch black. Conversely, you may have an
    observing spot that is free of local light pollution, but close enough to a city center that the
    whole sky glows yellow from horizon to horizon.

    Measuring light pollution

    It's helpful when discussing light pollution to be able to measure it objectively so that you can
    compare notes on equal footing with your fellow astronomers. It is also useful to be able to denote
    the light pollution levels in your observing notebook, so you can compare and contrast what you're
    able to see under different skies.

    There are three commonly used ways of measuring light pollution levels; each have their pros
    and cons.

    • Limiting Visual Magnitude (LVM) - This method is a good way of measuring both the light pollution levels and the level of your dark adaptation. Unfortunately, they get rolled into a single value, so you can't really tell your dark adaptation and the light pollution levels apart. The method is simple: you find a constellation of stars with known magnitudes, and find the faintest one you can see with direct vision. For consistency, it helps to use a constellation that is in the same part of the sky each night. For example, here is a chart for Ursa Minor that can help you find LVM for your site: http://www.satobs.org/image/nmag_guid.gif
    • The Bortle Scale - While the LVM method looks and feels objective, the resulting number you get doesn't really help much when trying to describe sky conditions to other astronomers. A slightly more subjective, but empirically more useful tool, is the Bortle dark-sky scale, published by John Bortle in the February 2001 edition of Sky & Telescope. The scale is numbered from 1 (excellent dark-sky site) to 9 (inner-city sky). Each of the nine levels of the scale have a paragraph describing the sky brightness that qualifies for that level. You can read about the Bortle scale on Wikipedia: Bortle Dark-Sky Scale - Wikipedia, the free encyclopedia. Note that the colors are not from the Bortle scale, but rather from the World Atlas of Artificial Night Sky Brightness. So saying that you have "Bortle Red" skies is inaccurate -- you have "Bortle class 7" skies, or perhaps WAANSB "red" skies.
    • Direct measurement - You can buy a tool called a Sky Quality Meter (Sky Quality Meter) that is able to directly measure the brightness of the sky. The result it returns is in magnitudes per square arcsecond. This is a completely objective (and useful!) measurement that can help you to determine whether a given object will be observable, by comparing the surface brightness of the object with the brightness of the sky. If the two values are more than three magnitudes apart, then you'll probably be able to see the object. Remember that surface brightness is not the same as integrated brightness! (see the "observing techniques" section further down).


    Dealing with light pollution

    Local light pollution is the easiest to deal with. The main thing that local light pollution is
    doing is hurting your dark adaptation. So if you can block the light from reaching your observing
    area, then you can fix that problem. Many observers set up tarps or curtains to block the light
    from neighbors' porch lights or from street lights. Others keep an eyepatch over their observing
    eye so that it stays dark adapted, and only pull the patch away while at the eyepiece. I often
    drape a dish towel over my head while observing from my backyard, to block the stray lights from the
    neighbors from interfering with my view through the eyepiece. Do what you've got to do!

    Regional light pollution is another story. The only way to deal with it is to get away from it (see
    the "selecting and utilizing a dark sky location" section below). But if you can't get out to a
    dark-sky site, there are a few things you can try:

    • Observe in the early morning hours before sunrise. Many businesses turn off exterior lights late in the evening, and there are fewer cars on the road with their bright headlights. In aggregate across the whole city, this can equate to darker skies than in the early evening just after the sun goes down.
    • Experiment with filters. Filters aren't a magic solution that makes all your problems go away, but if you are able to properly dark adapt (by eliminating local light pollution) then you might be able to tease out more detail on some objects (notably emission and planetary nebulae) by using a narrowband or line filter. A LPR filter might help improve contrast on other objects.
    • Choose targets that are easiest to observe under light pollution. Globular clusters and planetary nebulae are both objects with high surface brightness, which helps them to punch through light pollution. Since globs are stellar in nature, ramping up the magnification (up to a 1mm exit pupil) makes the background darker, but does not dim the constituent stars. This improves contrast and makes them easier to observe. Planetary nebulae respond very positively to narrowband and OIII filters, and also require high magnification. The combination makes them more observable in light polluted areas.



    Atmospheric Conditions

    Light pollution is just one of many atmospheric conditions that you deal with when observing.
    There are four properties to track, which the Canadian weather office does a great job
    of describing: Astronomy Sky Condition - Environment Canada -- click on each of the "forecast" links to find out more about how that part of the forecast impacts your ability to observe.

    Briefly,
    • Clouds: Obviously fewer clouds == more clear sky, and better observing conditions.
    • Seeing: How stable the air is. Poor seeing conditions cause stars to appear to be "boiling" when observed at high power. Good seeing is most important for observing things that require high power: double stars, planets, globular clusters, and planetary nebulae.
    • Transparency: Suspended dust and moisture in the air can scatter light, making light pollution worse and reducing the number of photons arriving at your telescope from the object you're observing. Good transparency is critical for detailed observation of faint objects like nebulae and galaxies. With poor transparency you can often still observe other objects effectively though, such as open clusters, double stars, and bright reflection nebulae.


    To find the sky conditions in your area and/or your favorite dark sky site, you can use the ClearDarkSky chart: Clear Sky Chart Homepage or 7Timer: 7Timer! - numerical weather forecast for anywhere over the world
    Last edited by skaven; 01-06-2013 at 12:13 AM.

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    Default Re: A Treatise on Optimizing DSO Observation

    Selecting and Utilizing a Dark Sky Location

    After reading through all this, you may have become (rightly) convinced that your backyard is not
    really the best place to be observing. You may be dealing with Bortle class 7-9 skies and all kinds
    of local light pollution from street lamps and porch lights. The houses around you create columns
    of hot air that make for poor seeing conditions. And the trees and buildings around you limit your
    view of the sky. So what do you do to get out to the "good stuff" under pristine dark skies?

    The first thing I recommend is that you search for an astronomy club in your area. Just hop over to
    Google and search for "your_city astronomers" and see what pops up. Astronomy clubs generally have
    a dark sky site that they use (or even own), and will be happy to have you join their ranks. This
    is the "fast track" way to dark sky -- let the folks that have been doing it for years do the
    hunting for you! As a side benefit, you'll have access to other astronomers so you can bounce
    questions off of them, try out equipment they bring to star parties, and even get access to club
    resources like loaner scopes, charts, and eyepieces.

    However, if the astronomy club hunt is a bust, or the site that they use is too far out of the way
    for it to be useful for you, then you may need to strike out on your own and locate your own spot.
    This can be a daunting challenge, but it's not impossible! Here are some tips and resources for
    finding a great dark sky spot.

    First, establish your goals, and the priority of those goals. There's bound to be trade-offs when
    you start locating potential observing sites. For example, "nearby, darkest sky, free to use...
    pick two". Not that it's always going to be like this, but it will serve you well in your hunt to
    ensure you've carefully considered what's most important to you, so that you can properly rank the
    sites you locate.

    To start, use the dark sky finder: Dark Sky Finder The data is a little
    old, but should be good enough that you can at least see the general regions around you that have
    dark sky. You may even find that there are already pins placed in the map in areas you are
    interested in, where other astronomers have registered an observatory or observing site. Use this
    site to identify a few key areas that you wish to narrow your search. The dark sky finder uses the
    World Atlas of Artificial Night Sky Brightness colors, which you can (loosely) cross-reference with
    the Bortle dark sky scale here: Bortle Dark-Sky Scale - Wikipedia, the free encyclopedia The Bortle
    designations can help you to get a feel for how "deep" you'll be able to go at a given site, based
    on the colors on the map.

    Next, visit Google Maps (Google Maps) or perhaps use Google Earth
    (Google Earth) to "fly" around your potential observing areas. You're
    hunting -- looking for parking lots, trail heads, pastures, turnouts, or anything else that might be
    a good spot to observe. As you find potential spots, jot down the locations. I like to use Google
    Maps' "my maps" feature to track my locations. Here is my dark sky research map:
    https://maps.google.com/maps/ms?msid...34ff22a1&msa=0

    Now that you have some potential spots located, you'll need to do some reconnaissance. During the
    day, drive by your potential spots. For each site, check for:

    • Legal to use: Respect "no trespassing" and "do not enter" signs. Don't cross fences. If there are gates, assume you're not supposed to go in there, unless it is explicitly noted otherwise. National parks are often great places to observe, but be sure you are following the rules. Do you need to buy an overnight pass? Are you allowed to stay after sundown?
    • Accessible: Are you able to safely get your car/truck into and out of the site? Do you think you'll be able to get in and out safely at night? If there are narrow roads, is there somewhere to turn your car around? You don't want to be backing down a narrow dirt road in the pitch dark...
    • Safe: Will you be secure in the location? Do you get cell phone coverage? How far away is the nearest 24-hour market? How about a local fire station or police station? It's unlikely that you'll need it, but when deciding on your dark sky site, remember that you're going to be there alone, and so something as seemingly trivial as slipping and falling could really escalate quickly if you don't have access to emergency services (or at least a cell phone signal).
    • Dark: Is it really dark there? There may be sites that seem like they'd be perfect. For example, on my map you can look at the "Sunrise Highway" location. It looks great -- high elevation, near a university observatory, with a large clearing/turnout that provides plenty of room to safely get off the road and set up the scope. But after trying the site one night, I found it wasn't as great as I thought. Cars driving up and down the road would constantly shine their headlights over the observing area. And the site, due to the high elevation, looks over a city below. The combination of the cars and the city lights combine to effectively thwart efforts to fully dark adapt. However, it does have an unfettered view of the western horizon, which makes it an ideal location to observe targets that only appear in the early evening low on the horizon.


    Once you have selected a site, and find that it is a good one, share it! If you know astronomers in
    your area, share your knowledge with them. You may find that after a while you can build up an
    astronomy club of your very own, just by virtue of coordinating trips to your newfound dark-sky
    site. Bringing more people with you (especially when they come in multiple vehicles) greatly
    reduces the risk of becoming stranded, and having other folks with you can be a lot of fun!

    The last thing I'll leave you with in this section is a checklist of items I bring with me to my
    dark-sky site. Your list will vary, but if you don't know where to start, this will at least get
    you going:

    • Telescope OTA
    • Finder
    • Eyepiece case
    • Accessories case (anti-vibration pads, laser pointer, Leatherman multi-tool, collimation wrenches, collimation tool(s), magnetic compass, extra batteries, a few Zeiss Lens Cleaning Wipes, pen, pencil, notepad)
    • Mount, counterweights, tripod
    • Battery
    • Charts
    • Dim red light (as a headlamp or on a lanyard so you don't misplace or drop it)
    • Mag-Lite (for a final scan of the area after observing to make sure you don't leave anything)
    • Electric/Wool socks
    • Wool cap
    • Sweatshirt(s)
    • Long johns/ski bib
    • Heavy coat (you should be dressing for ~20 degrees F colder than the "low" listed in the forecast)
    • Gloves
    • Bug spray
    • Thermos of hot tea
    • Water
    • Snacks
    • Kleenex (both for the nose and just in case you have to "pop a squat" in the woods)
    • Folding table (for charts and eyepiece case)
    • Observing chair (a drum throne is an inexpensive and quite portable solution if you're short on space)

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    Default Re: A Treatise on Optimizing DSO Observation

    Observing Techniques

    Visual observing, to a large degree, is more of an art than a science. I say that because it takes
    practice, finesse, and sometimes, a gut instinct, to do it well. Beginners are rarely able to just
    walk up to a telescope for the first time and see the with the same clarity, depth, and detail as an
    experienced veteran.

    So more than anything, be patient with yourself. Be persistent and get your scope outside whenever
    you can, and practice! You'll be pleasantly surprised that it gets to be easier and easier, and
    that you start to see more and more.

    As you work your way up the learning curve, here's a list of things to try to help you refine your
    technique.

    Make a plan

    It really helps you to relax when you've got a plan. Ad-hoc observing sessions tend to be frought
    with frustration. What's the best thing to observe tonight? Is there anything that is about to
    be below the horizon for the rest of the year? Are there any really interesting conjuctions
    occurring? All of these questions will be running through your head while you are at the scope.
    And even as you do get new objects lined up in the eyepiece, in the back of your head you'll be
    constantly thinking, "maybe there's something better to look at??"

    So -- make a plan! It doesn't have to be super-complex...perhaps just open up Stellarium and
    jot down a few objects you want to observe. Many astronomy applications (particularly those
    for your tablet and phone) have a "what's up" feature that can help you pick out a few objects
    to observe (but leave the phone/tablet turned off while outside with the scope!)

    For a complete discussion of developing an observing plan, see below. For now, just keep in mind
    that having a plan -- even just a scrap of paper with 4 or 5 objects listed -- can make you
    more relaxed at the scope. And a more relaxed observer is a better observer!

    Locating objects

    Locating objects can be tough. There's a LOT of sky up there, and in many cases the object
    you're trying to find is REALLY small. And even worse, the object is often just barely
    visible.

    So other than just punching in the objct number in your handbox and letting GOTO do the work,
    how do you find objects?

    First, I strongly urge you to get a Telrad, or a Rigel QuickFinder, or any other kind of
    "unit power reflex sight finder". Frankly, I think the Telrad is the best of the bunch,
    and at USD $40 is quite a bargain. The Telrad is an indispensable tool for helping you to find
    objects. It, along with a good set of charts (I recommend the Sky & Telescope Pocket Sky Atlas) is
    sufficient to locate pretty much everything in the Messier catalog, and then some!

    The trick is practice -- there's a number of different strategies for finding objects when using a
    Telrad + 8x50 finder. Here's two that I commonly use:

    1. Dead reckoning

    With this method, you look at your chart (it helps to make a Telrad "template" from a sheet of
    transparency paper so you can overlay the Telrad rings on the chart) and center the object in the
    Telrad rings. Look at neighboring bright stars and try to fix their positions in your mind. For
    example, the outer ring may be just to the "left" of a bright star, or something like that.

    Then swing your scope around and position the Telrad bulls-eye as best you can emulate from the
    charts. This will generally get the object at least within the field of your finder, where you
    can then adjust to center the object, and switch to a low-power eyepiece in the scope.

    This method is described in the O'Reilly book "Telescope Hacks": Hack 20. Locate Objects Geometrically

    2. Star hopping

    If dead reckoning doesn't work, then you have to star hop. But luckily, you can probably use the
    dead reckoning process to at least position the scope in the general vicinity of your target, then
    switch to your 8x50 finder. In the finder, you'll be able to see more stars, and should then be able
    to follow unique patterns and shapes of stars from one defined spot to another, until you arrive at
    your target.

    There is a pretty well thought out video series about star hopping on YouTube:



    You might also read through the Wikipedia article: Star hopping - Wikipedia, the free encyclopedia


    Have a seat and take your time

    It's tough to over-emphasize the importance of sitting while you observe. Not only does
    sitting save your back and neck from strain, the stability you get at the eyepiece equates
    to seeing more of those faint fuzzies. It's often said that just having a seat is like
    adding 2" of aperture to your scope!

    What are your options for chairs?

    • Drum throne: portable and sturdy. But often has a limited range of height adjustment. This can be a drag when using a refractor, where the eyepiece can move up and down by a large amount.
    • LYBAR chair: simple and inexpensive to construct yourself. Gives you three different height options. Might be difficult to pack in a car, though.
    • Denver Observing Chair: Wide range of height adjustments, and relatively lightweight considering its size. Rear support sticks waaay back, so you need a lot of room around your scope.
    • CATSPERCH Chair: Locking notches behind the seat keep it from sliding down unexpectedly. More compact than the Denver chair, but arguably a bit less stable, especially at high seat settings.


    In all cases, you are encouraged to try your hand at building your own if you don't feel like
    buying. Heck, even an overturned 5 gallon bucket or milk crate might be all you need to get into a
    comfortable position at the scope. Get creative! But whatever you do, have a seat.

    Eliminate stray light around your eyes

    While observing, you'll be surprised how much of a difference it makes, even under dark sky, to
    shield your eyes. While sitting in front of the eyepiece, lower your observing eye over the
    eyelens. Once you have the field in view, put both hands up around your face, like blinders. The
    natural tendency is to cup your hands closely around your eye -- you want to avoid this, because you
    don't want your hands resting on the telescope itself (that would introduce vibrations). Instead,
    just try to "float" over the eyepiece, with your hands on the sides of your face to block the stray
    light. You might find that the contrast level improves noticeably.

    Use long gazes and averted vision

    Once you have your target in sight through the eyepiece, really take some time to study it
    carefully. Spend at least 60 seconds at the eyepiece soaking in the view. Carefully scan over the
    whole surface of the object with direct vision. What can you see? Are some spots darker than
    others? Can you trace the perimeter of the object?

    Now avert your gaze 15-20 degrees to the side of the object, while still focusing on it mentally.
    You'll immediately notice the object appear brighter, possibly with more detail. Spend some more
    time observing the object with averted vision. Try moving your gaze closer to and further away from
    the object. Is there a "sweet spot" where you can see the most?

    By now you should have spent at least 120 uninterrupted seconds at the eyepiece. Take a few deep
    breaths, blink a few times, stretch your neck, and do it all again. You may see even more the
    second time around!

    Keep a logbook

    As you observe, it is a great idea to keep a log book. The log entries don't have to be novels:
    just keep an organized log of your attempted and successful observations. Often just a couple lines
    in a college-ruled notebook is sufficient.

    There are a few items that you can jot down just once, as you begin the session:
    • Date
    • Location
    • Weather/sky conditions (clouds, transparency, seeing, temperature, humidity, moon phase)
    • Telescope(s) being used


    And for each object you attempt to observe,
    • Object name/number
    • Magnification(s) used (or eyepieces if you prefer)
    • Filter(s) used (if applicable)
    • A brief 1-3 sentence description of the object, with emphasis on observable detail and structure. If you were unable to locate the object, note this as well.


    By keeping a logbook, you can monitor your progress over time. It also gives you a way to track
    information that is otherwise easy to forget. For example, when making an observing plan, you might
    not remember whether you've seen M36 yet. Was it M37? I know it was in Auriga, but which one?
    Well, you can go back to your log book and find out. And furthermore, you will be able to look up
    the circumstances around that last observation. Was it washed out and boring due to the light
    pollution? Perhaps it's worth a revisit if you're heading out to your dark-sky site.

    Try sketching

    In addition to keeping a log book, many amateur astronomers sketch the DSOs that they observe. The
    rigor required to transfer what you see in the eyepiece to a piece of paper demands a great deal
    more attention to what you are seeing in the eyepiece. And this very fact, regardless of how
    realistic your sketches end up looking, is a benefit.

    My logbook has a 2" diameter circle next to each log entry. I don't sketch everything that I
    observe, but having it right there in the log book is really handy for those that I do. And keeping
    the sketch in the logbook can help even more when going back to previous observations to see if you
    did, indeed, see more detail this time than last time.

    You don't need fancy tools to sketch, either. You can make perfectly great sketches with just a
    fine felt-tip pen (for plotting stars) and a standard No. 2 pencil. If you find you enjoy
    sketching, you could upgrade to a set of artists' pencils, or possibly even charcoal.

    Whatever you do, have fun!

    Understand Integrated brightness, Surface brightness, and Contrast

    When looking through a list of potential targets, and while at the eyepiece, it is important
    to have a grasp of the optical principles of integrated brightness (the total amount of
    light coming from an object), its surface brightess (the brightness of a single "spot"
    on the object's surface), and contrast (how much brighter the object appears than the
    background).

    Understanding these factors, and how they vary for different objects, can help you to
    make good decisions regarding the eyepiece to use when observing an object, as well as
    selecting the right time and location to maximize the chance that you'll have an enjoyable
    experience observing.

    Rather than try to paraphrase Tony Flanders' fantastic write-ups on these topics, I'll
    just link you to them. Both of these articles are absolutely worth the read:



    I'll quote Tony here to emphasize the importance of understanding how brightness works
    at the scope:

    Quote Originally Posted by Tony Flanders
    A great deal of confusion ensues from the fact that amateur astronomers habitually fail to specify
    whether they mean integrated brightness or surface brightness when they say that an object is bright
    or faint. Consider, for instance, M33, the Triangulum Galaxy. At magnitude 5.7, it is fifth in
    integrated brightness of any galaxy in the sky, after our own Milky Way, the two Magellanic Clouds,
    and M31, the Andromeda Galaxy. Nonetheless, M33 is referred to as a faint galaxy, because its light
    is spread out over a huge area -- nearly a square degree -- giving it one of the lowest surface
    brightnesses of any Messier object. On the other hand, the planetary nebula M76 has one of the
    highest surface brightnesses of any nebulous Messier object, but it is often called faint because of
    its low integrated brightness. (For mathematicians, the term integrated brightness refers to the
    integral of the surface brightness over the object's area, which in the case of M76, is tiny.)

    To make matters worse, amateur astronomers frequently use the term brightness to mean both
    integrated brightness and surface brightness in the same paragraph, and also often use it to denote
    the subjective impression of brightness, which depends both on surface brightness and on integrated
    brightness. Thus, the galaxy M33 and the globular cluster M13 have almost identical integrated
    brightness, but M13 appears much brighter both to the naked eye and through any optical instrument
    because its light is concentrated in a smaller area, i.e. because it has a higher surface
    brightness. But M13 also appears much brighter than the globular M28, which has almost identical
    surface brightness, because M13 is much bigger, and so has higher integrated brightness.

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    ES 70° 15mm, 20mm; ES 82° 30mm, 18mm; ES 100° 9mm; Baader Hyperion 24mm; TV Nagler T6 13mm
    William Optics Binoviewer; GSO 2" 2x ED barlow; 5x APO barlow, Parks 2.5x APO barlow
    Filters: Orion Ultrablock, Thousand Oaks OIII

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    Default Re: A Treatise on Optimizing DSO Observation

    DSO Catalogs, Star Charts, and Software Tools


    DSO Catalogs

    If you are just starting out, you might feel a bit overwhelmed. There are literally thousands
    of objects visible in a typical amateur class telescope. It takes years of careful and methodical
    observation to even make a dent in that list. So where do you start? How do you decide what to
    observe this year, much less tonight?

    Luckily, there are veteran astronomers that have done a lot of this work for us already, by creating
    catalogs of objects. Sometimes the catalogs have a theme (like the Struve catalog, which tracks
    double stars, or the Arp catalog, which tracks irregular galaxies). Other catalogs are simply collections
    of "pretty" things to look at.

    Each catalog generally assigns a catalog-specific designator to each objects. Generally this catalog-specific
    designator is cross-referenced to at least the New General Catalog (NGC), which is, for the purposes
    of amateur astronomers, the de facto clearing house for all observable DSOs.

    It's handy to have a set of catalogs at your fingertips when planning observations. For example,
    let's say you're planning a trip to a very dark site. You'll probably want to look for a catalog
    that lists objects that you may not be able to see from light polluted skies (such as the Caldwell
    or Arp catalogs). If you just got a shiny new APO refractor, you might browse through the Struve
    catalog and look for colorful doubles to split.

    I present to you here a few catalogs that I've found handy. It's by no means complete or authoritative,
    it's just a place to start.

    Messier Catalog - SEDS Messier Database

    From the SEDS site:

    During the years from 1758 to 1782 Charles Messier, a French astronomer (1730 - 1817), compiled a
    list of approximately 100 diffuse objects that were difficult to distinguish from comets through the
    telescopes of the day. Discovering comets was the way to make a name for yourself in astronomy in
    the 18th century -- Messier's first aim was to catalog the objects that were often mistaken for
    comets.
    One of the great things about the Messier catalog that makes it so popular is that because it was
    compiled so long ago, on (by today's standards) such primitive telescopes, most of the objects in
    the catalog are visible using equipment well within the reach of an amateur astronomer. The majority
    of the catalog can even be observed using a 10x50 binocular!

    Plus, the list is relatively short (110 objects) and so it is not a monumental task to work through
    the entire catalog over the course of a year or two. But it is actually possible to observe the
    entire catalog in a single evening -- these events are called Messier Marathons.

    Caldwell Catalog - Caldwell catalogue - Wikipedia, the free encyclopedia

    From the Wikipedia page:

    The Caldwell Catalogue is an astronomical catalog of 109 bright star clusters, nebulae, and galaxies
    for observation by amateur astronomers. The list was compiled by Sir Patrick Caldwell-Moore, better
    known as Patrick Moore, as a complement to the Messier Catalogue.
    The Caldwell catalog is a great place to start once you have exhausted the Messier catalog for things
    to see. It, too, is a short list, and can be worked through in a year or two of dedicated observing.

    Herschel Catalog - http://obs.nineplanets.org/herschel/h2500.txt

    From http://en.wikipedia.org/wiki/Catalogue_of_Nebulae:

    The Catalogue of Nebulae and Clusters of Stars was first published in 1786 by William Herschel in
    the Philosophical Transactions of the Royal Society of London.[1] In 1789, he added another 1,000
    entries., and finally another 500 in 1802, bring the total to 2,500 entries.
    This is a massive catalog. In the eighteenth century, this was one of the major efforts to
    catalog everything visible in the sky under a single catalog. It is so big, however, that
    it's often broken up into smaller chunks. The
    Herschel 400 is a subset of the full
    Herschel catalog compiled by Brenda F. Guzman (Branchett), Lydel Guzman, Paul Jones, James Morrison,
    Peggy Taylor and Sara Saey of the Ancient City Astronomy Club in St. Augustine, Florida, USA in
    around 1980. It identifies the 400 "best" objects in the Herschel catalog. It overlaps quite a few
    items in both the Messier and Caldwell catalogs.

    Astroleague Catalogs - Observing Clubs

    The Astronomical League is a worldwide society devoted to promoting the science of astronomy. One
    of their many efforts has been to create a series of "clubs" that each consist of a series of
    "programs". Each of these programs is a catalog of sorts -- a series of observing challenges that,
    if accomplished, is rewarded with a certificate and a "badge" of sorts.

    It is not necessary to join Astroleague to get access to their observing lists. These catalogs
    are an excellent resource for beginners who do not want to get frustrated trying to observe objects
    that are not suited to either their light pollution levels or their equipment.

    Struve Catalog - Complete Struve Catalog, Double Star Abbreviations, and other Double Star Info

    This is a catalog of double stars. If you love splitting doubles, this one is for you.

    Arp Catalog - Arp's Catalog Of Peculiar Galaxies

    This catalog compiles irregular and unusual galaxies. Many (if not all) are challenging in typical
    amateur equipment -- you need a pretty big scope to observe these visually. But if you are doing
    astrophotography, this could be a great catalog for locating interesting things to image

    RASC Observer's Handbook - Observer's Handbook | The Royal Astronomical Society of Canada

    This isn't a catalog, per se, but it is an indispensable resource for an amateur astronomer
    wishing to learn more of the science of astronomy. The handbook includes ephemera for the year,
    including tides, moon phases, planetary positions, conjunctions, eclipses, occultations, asteroid
    passes, and star charts. It also includes an entire section with scholarly papers written by
    professional astronomers and astrophysicists. The 2012 edition, for example, included a fantastic
    paper by Roy Bishop about the science behind how exit pupils affect your view through a telescope.

    In the back of the book are a series of observing lists, sorted and compiled specifically for
    North American observers. Some of these lists, such as "Finest NGC objects" and "Deep Sky Gems"
    are excellent resources when planning an observing session.


    Star Charts

    As I have mentioned many times in this treatise, using electronic tools (smart phone, tablet,
    laptop) while at the scope is a recipe for frustration, mostly due to the ease with which
    these devices can rob you of your hard-won dark adaptation. Using a paper star chart and
    a dim red light is (in my opinion) a much better way to navigate the skies while at the
    scope.

    There are many star charts with various pros and cons, but I'll try to summarize the ones
    I am familiar with here.

    Sky & Telescope's Pocket Sky Atlas - This is a fantastic atlas in that it's compact,
    spiral-bound, and rugged. It isn't the most detailed chart, but really hits a lot of sweet
    spots when observing. You can work through the entire Messier and Caldwell catalog with
    just this atlas at your side, if you choose.

    Sky & Telescope's Sky Atlas 2000.0 - The big brother of the Pocket Sky Atlas. If
    you have a PSA and want to go "deeper", this is a great atlas, because the symbols, markup,
    fonts, and everything else you're used to in the PSA, will be the same in this atlas, just
    "zoomed in" further, and with fainter stars plotted.

    Uranometria 2000.0 Sky Atlas - Goes even deeper than the S&T Sky Atlas. It goes so
    deep that it actually comes in three volumes!

    The Triatlas Project - This is a free
    atlas that you can download. It comes in three volumes. The "A-set" is a broad view that
    sits somewhere between the PSA and the S&T Sky Atlas. The "B-set" goes even deeper, and
    finally the "C-set" goes all the way down to magnitude 12.4. If you can't afford a big
    professionally bound atlas, you can at least print off a page or two from the Triatlas
    before each observing session to give yourself a map.


    Software Tools

    Given that astronomy is a science, it should be no surprise to discover that there is
    a wealth of excellent software available to assist you in various aspects of the
    field. You might be able to put web sites under this category as well, but I will
    refrain from doing so -- see the "Links and Resources" section at the end for those.

    Stellarium - Stellarium

    A fantastic planetarium program. Notice I didn't call it a "chart generation" or
    "observation list generation" tool. Stellarium's purpose is more to be a realistic
    simulation of what it's like to stand outside and look up at the sky, than it is
    a "charting" tool. However, despite that, it is immensely useful for predicting
    when objects will be visible, in which part of the sky. And the Oculars plugin
    can give you a real-time peek at how different telescope and eyepiece combinations
    will frame your target. You can even control your computerized telescope with it.

    One great thing about Stellarium is the ease with which you can customize it. Two
    customizations I have made have been to add custom landscapes and to add a new
    "Skyculture" that draws the constellations using the Sky & Telescope figures.
    You are welcome to use both!



    Cartes du Ciel - start [Skychart]

    This software is more along the lines of what you'd expect from a "chart generation"
    tool. It doesn't try to simulate the view of the night sky, but rather gives you
    a powerful interface for locating, researching, and plotting the locations of objects.

    The Sky - TheSkyX Professional Edition - Software Bisque

    A limited/trial edition of this software is often bundled with new telescopes. It's actually
    pretty nice software, bridging the gap between a "planetarium" program like Stellarium and
    a "charting" program like Cartes du Ciel. It's a professional-grade piece of software
    that isn't free, but doese have everything in it you might need to control your high-end
    robotic astrophotography rig.

    Software Forum - Astronomy Software Forum

    Software is constantly changing and improving. If you discover some great new software,
    or want to discuss it, visit this forum's software section and post a new thread!
    dhanson, fogfire, Philip F and 9 others like this.

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    C10-N/C14+Losmandy G11; Portaball 12.5"; NexStar 6SE; Meade ETX125; Stellarvue F80
    Meade HD-60 9mm, 6.5mm; 56mm; University Optics Orthoscopic 12.5mm, 9mm, 7mm, 5mm;
    ES 70° 15mm, 20mm; ES 82° 30mm, 18mm; ES 100° 9mm; Baader Hyperion 24mm; TV Nagler T6 13mm
    William Optics Binoviewer; GSO 2" 2x ED barlow; 5x APO barlow, Parks 2.5x APO barlow
    Filters: Orion Ultrablock, Thousand Oaks OIII

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