Today @Cosmic_Background captured a beautiful image of the Transit of Mercury.
Although the last transit of Mercury occurred only three years ago, the next won't happen until 2032 and won't be visible from North America.
Because Mercury is closer to the sun than Earth, Mercury constantly passes between our planet and our star. But its orbital plane doesn't quite line up with Earth's, so most of the time it appears to dip either above or below the sun when seen from our planet. Only when Mercury's orbit crosses the plane of the Earth as it appears in line with the sun is a transit visible. Such transits are rare; this will be the fourth of 14 to happen this century. Venus also transits the sun, but even more rarely, occurring in pairs separated by a century from the last set.