There's a Little Black Spot on the Sun Today

A man by the name of Gordon Sumner wrote those words some time in the early 1980s. They were especially applicable yesterday (May 9, 2016) because there was in fact a little black spot on the Sun, and not an ordinary one.

There are almost always areas of intense magnetic activity on the surface of the Sun that appear as small, black, irregularly-shaped spots. We refer to them sunspots. But the little black spot in question yesterday was an interloper, an intruder, a wanderer... and extremely circular in appearance. It was the planet Mercury.

Mercury, being the closest planet to the Sun, transits the face of the solar disk now and then, every few years or so. The only other planet to do this is Venus. Venus transiting the Sun is a much rarer occasion. It last occurred in 2012 and won't happen again until 2117.

Actually, all planets transit the Sun, just not from our perspective here on Earth. Many events in the solar system are a matter of perspective. We can only see Mercury or Venus transit the Sun because they are the only planets that ever get between the Sun and us since they are the only planets closer to the Sun than us. The Moon can also transit the Sun but we refer to that as an eclipse. An eclipse is a transit, but because of our perspective, the Moon appears about as large as the Sun in the sky, and has the ability to fully or partially eclipse it.

But back to the transit... Here's a video showing all ~6 hours of the transit (sped up, of course) along with some scenic time lapse and aerial shots.

Mercury's "3rd contact" as it exits the face of the Sun.