Mercury

Mercury never strays far from the Sun, so it is only seen in twilight: in the west after sunset or in the east before sunrise. It is easiest around greatest elongation, when it is farthest from the Sun in our sky.

Upcoming greatest elongations: October 12, 2026 (evening, 25° from the Sun); November 20, 2026 (morning, 20° from the Sun); February 3, 2027 (evening, 18° from the Sun). How high it gets also depends on your latitude and the season.

Mercury is the smallest planet and the closest to the Sun. It races around its orbit in 88 days, faster than any other planet, which is why the Romans named it after their swift messenger god.

Because it never strays far from the Sun in our sky, Mercury is only visible low in twilight: just after sunset or just before sunrise, for a week or two at a time. Many people who watch the sky for years have never knowingly seen it.

Up close, Mercury looks a lot like our Moon: gray, airless and covered in craters. With almost no atmosphere to hold heat, its surface swings from about 430 °C in sunlight to about −180 °C at night.

Mercury spins slowly. One full day, from sunrise to sunrise on its surface, lasts about 176 Earth days, longer than its year. Two spacecraft have mapped it so far, and a third, BepiColombo, is on its way into orbit.

Mercury has a very large iron core for its size, and NASA’s MESSENGER spacecraft found evidence of water ice hidden in permanently shadowed craters near its poles, despite its closeness to the Sun.