Sunday, 1 May 2016

Is that Mercury?

The upcoming transit of Mercury (9th of May) falls at a great time. It can be seen, at least partially, across much of Asia, Europe, Africa, North & South America. Sorry Australia, you miss out on this one.

For details, see:

Like a partial solar eclipse, observing the transit requires looking at the Sun. Looking at the Sun is a dangerous  activity without the proper equipment. If you don't have a proven solar observing system in place, then seek out someone that does to see the transit.

So what makes up a proven solar observing system?
McMath-Pierce Solar Observatory

How about Solar (Eclipse) Glasses? - Not good enough. You will need magnification to see the Mercury transit.

Mercury is very small. Even at the closest point it is only 1/150th of the size of the Sun. That is too small to see. The human eye can resolve about 1-2 arc minutes at best (ref.). The Sun ends up being about half a degree (30 arc minutes, 1800 arc seconds) in size up in the sky. Mercury is a mere 12 arc seconds.

You will need a telescope.

Please remember, solar glasses are NOT TO BE USED WITH A TELESCOPE.

Solar filter on a telescope?
Might be good enough, with some magnification. You will need about 50x to see the dot clearly. Higher magnification reveals a small disk. And it can be easily mistaken for a sun spot.

My favorite method of observing a transit is to use a projection set up. Any telescope, carefully monitored, can be used to produce a clear image of the solar disk. Practice is always recommended and be careful. Having the telescope pointed at the Sun is potentially dangerous and should be done in short intervals to avoid heating the optics or tube too much. Use extreme caution.

Transit of Venus projection

The transit is a rare event. Only a dozen or so times per century can one see Mercury go across the Sun. If you have a proven solar observing system or know someone who does, try to catch on the 9th of May. In Jamaica it will be taking place shortly after sunrise. We normally have clear sky in the morning so I hope to get a few images. They will be posted to this blog of course!

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