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Thread: Transit of Mercury - Magnification Needed?

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    Default Transit of Mercury - Magnification Needed?



    Hello Forum,
    Having missed both transits of Venus I'm now looking forward to being better prepared for the transit of Mercury in 2016. Looking at pictures I notice that Mercury is a very small dot against the disc of the sun, which is not surprising considering the size of that planet.

    So I'm wondering if it's resolvable with normal vision? If I use just a pair of good eclipse glasses will I still be able to see it, or do I need magnification? I'll most likely have a telescope by then, but if I travel to a less cloudy location than Finland that could be of limited use.

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    Default Re: Transit of Mercury - Magnification Needed?

    mercury.jpgscreenshot Stellarium

    You'll need some magnification!

    Mercury will be 12 arcseconds big. 60 to a 100 times magnification would be nice, I think.

    Clear skies to you!

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    Default Re: Transit of Mercury - Magnification Needed?

    I don't know for sure, but I'm guessing you'll need some sort of magnification. Before the Venus transit, the same question was asked about Venus and some of the members ran the calculations that suggested it was just on the border of detectible (I was able to see it without magnification while wearing my contact lenses that give me 20/20).

    Mercury is much smaller, in addition to being farther away. I would think you could still see it with a pinhole projection setup which provides some enlargement, but again don't know for sure.

    I was lucky enough to catch the second transit, and can tell you it's definetly a sight to see! IMO, the only acceptable excuse for not seeing it would be clouds. If you need magnification to see it, just buy the cheapest binoculars that would give you enough mag and project the image that way.
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    Default Re: Transit of Mercury - Magnification Needed?

    Venus was easily visible without magnification. Mercury will be a bit trickier, and might present challenges to those with astigmatism. My guess is that quite a few people wll be able to see it with just eclipse glasses.
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    Default Re: Transit of Mercury - Magnification Needed?

    Venus was 58 arcseconds across during the last transit. That is 4.8 times wider than Mercury will be.

    The apparent surface of Mercury's disc will appear 23 times smaller than that of Venus during its last transit.

    The native resolution of the eye is about 1.2 arcminutes at best (50 line pairs per degree, according to wikipedia). The disc of Mercury will be 6 times smaller than that.

    I recommended 60x or more magnification because I imagine you want to see more than a black point. 60x will turn Mercury into a nice small black disc, with the full face of the Sun visible at the same time.

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    Default Re: Transit of Mercury - Magnification Needed?

    I think I'll make sure I have some magnification handy. I suppose that means a telescope since few binoculars are readily adaptable for solar viewing.

    At least I have plenty of time for preparations.

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    Default Re: Transit of Mercury - Magnification Needed?

    "Seeing" is a loose term for this purpose. Normal good eye vision can "resolve" at about 1 arc minute. Some eyes are better than others. That means that one can tell a line exists across a background if the line is 1 arc minute wide. This is measured by placing a black line on a white background and illuminating the surface equally. But we see stars that are much smaller because there is much more contrast.

    But our eye isn't as good looking at a black spot against a bright background as it is with a star against a black background. To be sure you can see a transit as a dark disc, you should have at least 4 resolution lines across the spot. This indicates you might need 6x to detect it and 24x to be confident. At 60x you should see it clearly as a disc.

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    Default Re: Transit of Mercury - Magnification Needed?

    Actually, I have seen commercially available solar filters for binocs. Here is an example. Might be more cost effective than a scope and solar filter.

    If you have already have binocs you could buy Baader solar film and either make filter holders or attach it over each objective with a rubberband.

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    Default Re: Transit of Mercury - Magnification Needed?

    Quote Originally Posted by cliffc321 View Post
    Actually, I have seen commercially available solar filters for binocs. Here is an example. Might be more cost effective than a scope and solar filter.

    If you have already have binocs you could buy Baader solar film and either make filter holders or attach it over each objective with a rubberband.
    Wow, it's not going to be too expensive either way!

    A small telescope on a small EQ mount with a solar filter will cost €138 in Finland.

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