On May 9th, 2016, Mercury made a transit in front of the Sun for the first time since 2006. The transit or passage of a planet across the face of the Sun is a relatively rare occurrence. As seen from Earth, only transits of Mercury and Venus are possible. There are approximately 13 transits of Mercury each century. In comparison, transits of Venus occur in pairs with more than a century separating each pair.
Mercury Transit 2016. Image credits and copyright: Sakari Ekko.
Sakari Ekko an astrophotographer and member of EAAE has made the fantastic image above, as he captured Mercury's transit in Turku, Finland, taking a photo every 20 minutes. Only the last 7 minutes of the transit were lost because the Sun was so low (altitude < 1º) and bad seeing washed out Mercury.