On May 9, 2016, over the course of seven and a half hours beginning at 7:12 a.m. EDT (11:12 UTC) Mercury passed across the disk of the Sun, appearing to observers on Earth as a small dark dot in front of the massive brilliance of our home star. While the event wasn’t visible to the naked eye (the Sun is just too bright and Mercury just too small) those with filtered telescopes and solar projection devices (like what I had set up) were able to see Mercury silhouetted against the Sun, and that most certainly included solar photography master Alan Friedman who captured the amazing image above from his home in Buffalo, NY.
Taken in hydrogen alpha, a wavelength of light emitted by ions in the Sun’s lower atmosphere, the image shows Mercury as a tiny dark circle just below center left of the Sun.
A little over 1,500 miles wide, Mercury is half again as large as our Moon and is about 2/5ths the distance from the Sun as Earth (0.38 AU.) If Earth were at that distance it would appear about five times larger—which, compared to the Sun, would still look pretty small.
Mercury passes in front of the Sun from the viewpoint of Earth only about 13 times every century. The last time it occurred was in 2006 and it will happen again in 2019. (Since Earth and Mercury are both in motion the event doesn’t occur on regular intervals.)
Skywatchers around the world enjoyed the opportunity to witness the daytime cosmic event, including myself… after sharing pictures of my homemade setup the local news meteorologist stopped by to do a story on it. (Thanks TJ!)
The transit was also observed by spacecraft in orbit—see a video from NASA’s Solar Dynamics Observatory below:
But there’s something extra special about amazing images captured by regular folks from their own backyards, and when it comes to our Sun Alan is a specialist.