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Thread: How much of our Universe is blocked from our view?

  1. #1
    Solrian's Avatar
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    Default How much of our Universe is blocked from our view?



    I don't remember seeing this subject here at AF, so here goes. The view of our surrounding Universe is partially obscured by our own Milky Way Galaxy. How much is blocked by the bulk of our home galaxy? Do we have any idea what is out there, in detail? I think radio telescopes can penetrate the dust. Does anyone have any thoughts about this? My ignorance is obvious!
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    Default Re: How much of our Universe is blocked from our view?

    love your question Jim.
    its a very good one.
    somewhere in this tired old brain, a bell is ringing.
    I thought I read very recently about some telescope that is seeing more than they have ever seen before looking towards the center of our galaxy.
    I think I remember something about infra-red.
    there might be a thread here about it.

    check this:
    https://en.wikipedia.org/wiki/Zone_of_Avoidance

    and this I think is from a recent thread:
    https://www.washingtonpost.com/news/...the-milky-way/
    Last edited by chas53; 11-07-2015 at 09:07 PM.

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    Default Re: How much of our Universe is blocked from our view?

    Well according to the article linked below the milky way blocks about 10-20% of the night sky.

    How do we see through our own galaxy? – Starts With A Bang
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    Default Re: How much of our Universe is blocked from our view?

    Yes, surprisingly little is blocked.

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    Default Re: How much of our Universe is blocked from our view?

    The observable universe consists of the galaxies and other matter that can, in principle, be observed from Earth at the present time because light and other signals from these objects have had time to reach the Earth since the beginning of the cosmological expansion. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe is a spherical volume (a ball) centered on the observer. Every location in the Universe has its own observable universe, which may or may not overlap with the one centered on Earth.

    The word observable used in this sense does not depend on whether modern technology actually permits detection of radiation from an object in this region (or indeed on whether there is any radiation to detect). It simply indicates that it is possible in principle for light or other signals from the object to reach an observer on Earth. In practice, we can see light only from as far back as the time of photon decoupling in the recombination epoch. That is when particles were first able to emit photons that were not quickly re-absorbed by other particles. Before then, the Universe was filled with a plasma that was opaque to photons.

    The surface of last scattering is the collection of points in space at the exact distance that photons from the time of photon decoupling just reach us today. These are the photons we detect today as cosmic microwave background radiation (CMBR). However, with future technology, it may be possible to observe the still older relic neutrino background, or even more distant events via gravitational waves (which also should move at the speed of light). Sometimes astrophysicists distinguish between the visible universe, which includes only signals emitted since recombination—and the observable universe, which includes signals since the beginning of the cosmological expansion (the Big Bang in traditional cosmology, the end of the inflationary epoch in modern cosmology). According to calculations, the comoving distance (current proper distance) to particles from the CMBR, which represent the radius of the visible universe, is about 14.0 billion parsecs (about 45.7 billion light years), while the comoving distance to the edge of the observable universe is about 14.3 billion parsecs (about 46.6 billion light years), about 2% larger.

    The best estimate of the age of the universe as of 2015 is 13.799±0.021 billion years but due to the expansion of space humans are observing objects that were originally much closer but are now considerably farther away (as defined in terms of cosmological proper distance, which is equal to the comoving distance at the present time) than a static 13.8 billion light-years distance. It is estimated that the diameter of the observable universe is about 28.5 gigaparsecs (93 billion light-years, 8.8×1026 metres or 5.5×1023 miles), putting the edge of the observable universe at about 46.5 billion light-years away.[
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    Default Re: How much of our Universe is blocked from our view?

    Quote Originally Posted by not_Fritz_Argelander View Post
    Yes, surprisingly little is blocked.
    Okay. Which devices can peer through the murk to show us what is actually there?
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    Default Re: How much of our Universe is blocked from our view?

    Quote Originally Posted by Solrian View Post
    Okay. Which devices can peer through the murk to show us what is actually there?
    A single device can't really cut through the murk. You can combine observations from multiple devices and correlate observations to do better at getting through the obscuration.

    The 21 cm line due to the spin-orbit coupling transition in neutral hydrogen is a good radio wavelength to operate at but you need to deconvolve the signal from the galaxy. So it only gets good for redshifts that are large compared to the rotation curve of the galaxy.

    IR observations do pretty well too but even though the link in post #3 is pretty optimistic, it has limitations.

    There is no single device that shows all. I just find it surprising we can see so much.
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    Default Re: How much of our Universe is blocked from our view?

    Okay. Which devices can peer through the murk to show us what is actually there?
    Near infrared scopes, aka the ones used by the old 2MASS survey, and the more recent Sloan Digital Sky Survey.

    My project touched upon this in a tangential way. I started getting concerned about light extinction (reddening) distorting the distances I was trying to compute for stars past 100 parsecs (within 100 parsecs, reddening is something you can almost discount.) For the B and V bands, reddening is dramatic - it can make a star appear to be of another spectral type and class altogether. But, for the J, H, and K magnitudes, reddening is vastly reduced, though not eliminated.
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    Default Re: How much of our Universe is blocked from our view?

    Quote Originally Posted by ThinkerX View Post
    For the B and V bands, reddening is dramatic - it can make a star appear to be of another spectral type and class altogether. But, for the J, H, and K magnitudes, reddening is vastly reduced, though not eliminated.
    To be precise reddening only changes the photometric colors. The spectral type is not changed, you can still get a valid spectral type for a rede need star. Reddening can change the colors so that the colors correspond to those of a different spectral type. An actual spectrum won't be fooled.
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    Default Re: How much of our Universe is blocked from our view?

    Here's an answer that is pure frustration.
    It doesn't matter what's stopping us see the universe, I can't even get past the clouds........
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