A rare cosmic event will occur on the morning of May 9, 2016. Mercury, the innermost, smallest, and speediest planet, will appear to cross the sun’s disk, as seen from Earth.
This event is called a solar transit. It can be safely observed only with telescopic projection or special telescopic filters that remove nearly all of the sun’s damaging rays.
Mercury and Venus are the only planets that orbit the sun inside of Earth’s orbit. So, as seen from Earth, they are the only planets that can transit the sun. Solar transits of Venus, a nearby planet almost as large as Earth, are extremely rare, but spectacular. The last transit of Venus occurred on June 5, 2012, but the next one won’t happen until December 11, 2117! Transits of Mercury happen more often. We had a chance to see one from Colorado on November 8, 2006. And, after the May 9th transit, we’ll get to see another one on November 11, 2019. But Mercury is only half as wide as Venus, and about twice as distant. So the disk of Mercury as it crosses the sun will appear quite small. A safely filtered telescope will be needed to see it.
On May 9, Mercury will first contact the eastern side of sun’s disk at 5:12 a.m. Mountain Daylight Time, before the sun rises at about 6:00 a.m. on the Western Slope. Moving from east to west, Mercury’s tiny disk will take seven and a half hours to cross the sun, finally moving off the solar disk at 12:42 p.m. M.D.T.
You can join members of the Black Canyon Astronomical Society and Sky Rangers to view the May 9 solar transit of Mercury through safe solar telescopes. Come to Black Canyon of the Gunnison N. P. South Rim Visitor Center between 8:00 a.m. and noon. Remember: Never look at the sun without using an approved solar filter. Severe eye injury can result.
Mercury transit web links of interest:
Western Slope Skies is produced by members of the Black Canyon Astronomical Society. This episode was written and recorded by Art Trevena.