Transit of Mercury across the sun
Because of its close proximity to the sun, Mercury is often lost in the glare and is usually best seen from Earth only when there is a solar eclipse. From the Northern Hemisphere, you can sometimes see it at dawn or twilight. Transits of Mercury only occur a handful of times within in a century, including one on May 9, 2016. A telescope with a solar filter is necessary to spot Mercury during a transit. Here, a time-lapse photo depicts Mercury crossing the sun in 2006. Mercury is the small black dot moving across the sun.