Transit of Mercury, 2016

Written by User 1

Last Updated: December 21, 2013, 09:08 pm (UTC)
Originally created on July 26, 2012

A transit of Mercury occurs when the planet Mercury passes in from of the Sun. This will occur on Monday, May 9, 2016 which will be the first such event in 10 years with the previous having taken place in 2006. The transit will last from about 11:12 UTC to 18:42 UTC with the exact timing depending on the location.

Visibility map of the transit The transit favors the Atlantic Basin with the entire transit visible over the North Atlantic. Furthermore, all of the Americas, all of Europe, most of Africa and parts of Asia will also be optimal for viewing a significant portion of the transit, weather permitting. Unlike lunar and solar eclipses which typically last a few hours at most (including the partial phases), this transit of Mercury will last 7.5 hours. This means at least part the event will be visible over a much wider area as the Earth rotates and new areas become visible. In fact, only Antarctica (where the sun does not rise in May), eastern Asia and Australia/Oceania will miss out on the event entirely with the event occurring while the Sun is below the horizon.

Transits of Mercury may occur in either May or November. During the May transits, Mercury is near its aphelion point and appears bigger than in November transits (12" vs. 10"). May transits, like this one, are also much rarer than the November transits which occur about twice as often. Both the transit preceding this one (in 2006) and the following three (in 2019, 2032 and 2039) are November transits. After this one, the next May transit won't occur until May 7, 2049 -- 33 years afterwards.

Weather Conditions

May is a month known for its "May Gray" along many coastal areas in the Northern Hemisphere caused by a temperature inversion of warm air over cool ocean water. While it provides relief from the almost-summer heat, the layer of clouds it produces can obliterate all traces of the Sun's disk rendering the transit invisible.

The "optimal" place the view the transit, accounting for weather conditions, would be in central Greenland in the middle of the ice sheet that covers most of the island. An alternative location that would theoretically work just as well is the relatively unstable territory of Western Sahara in western Africa.

For the majority of us that aren't willing to travel to such extreme places, other weather-favorable locations that see a substantial part of the transit include the Atacama Desert in Chile (transit finishes at sunset), the Mojave and Sonoran deserts of southwestern North America, including Baja California (sunrise 1.5 hours after ingress), anywhere in the Sahara Desert (sunset 0-2 hours before egress), the Kalahari Desert (sunset 3 hours before egress) and the eastern Arabian Desert (sunset 3.5 hours before ingress).

This map shows the mean afternoon cloud cover for the month of May:

Cloud Cover in April

Viewing the Transit

Transits of Mercury require a properly filtered telescope to see. During this transit, Mercury will have an apparent diameter of approximately 12" compared to 1902" for the Sun. As a result, it have a diameter just 0.63% that of the Sun. Solar glasses, such as those used for viewing solar eclipses and the transit of Venus, are inadequate for viewing Mercury as the planet will be far too small to be visible.

Alternatively, it is also possible to use a telescope to project an image of the Sun onto a white screen so that everyone can see it. To do so, simply point the telescope at the Sun without looking into it and place a white screen (like a piece of paper) several inches away from the eyepiece. Once focus is achieved, an image of the Sun should be visible on the screen.

For more tips and details on safely viewing the Sun (including transits/eclipses involving the Sun), see the info page about the Sun.

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