Thursday, 21 April 2016

Transit of Mercury 2016 May 9

On the 9th of May (this year) there will be a rather rare event. The planet Mercury will transit the face of the Sun. This does not happen every time Mercury passes between the Earth and Sun. The distances and sizes are very large.

Mercury, even when closest to Earth, is a mere 11 arc seconds in size. For comparison, the Sun is half a degree (30 minutes or 1800 seconds) in size. In addition, the inclination of Mercury's orbit is 7 degrees meaning that it misses the solar disk by up to 14 times the size of the Sun. (More Mercury facts available at: http://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact.html

After this transit of Mercuy, the next one will be in 2019 then we wait until 2032. There are only 14 transits of Mercury this century. Here is a list of Mercury transits.

Okay, so a transit of Mercury is rare. But is it spectacular? Well, to be honest, no it isn't. You need a telescope to see it. And at that, a safe solar telescope with either a good solar filter or set up for projection. The picture below is one taken through a small telescope. Mercury is the little dot (shadow) on the edge of the Sun on the bottom right of image.

Mercury Transit - Questar prime focus

Thus I cannot say it is worth getting too worked up about unless, like me, you marvel at the ability of science to predict such things and our ability to see it. These are things that only came about in the past couple centuries. People have not been watching Mercury transit the Sun for many generations and you could end up being the first ever in your family to have seen one. If you have the right gear, then by all means get set up for it (if clear and you are on the right side of the Earth - check the transit visibility map here) and share the experience with others. For real geeks, here is an online Mercury transit calculator with great details from your (or a specific) location.

For us, the transit will be visible in the morning hours which works out best. We have the clearest sky in the morning and should be able to see the entire transit. The problem will be clouds over the hills to the East of us, if any.

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