Planet Closest to the Sun

The planet closest to the Sun is Mercury, which can get as close as 46 million kilometers from the Sun. Just for comparison, the Earth orbits at an average distance of 150 million km. Since Mercury orbits so close to the Sun, it only takes 88 days to complete an orbit – one quarter of an Earth year.

And there's another thing about being so close to the Sun; it gets really really hot. Daytime temperatures can soar to 700 Kelvin at the equator. Since Mercury doesn't have an atmosphere, parts of the planet in shadow dip down to 100 Kelvin (-173 degrees C). Even though Mercury is the planet closest to the Sun and orbits quickly, it has a very long day. In fact, a day on Mercury lasts almost 116 days. Its day is longer than its year.

Want to see Mercury for yourself? You can, but you have to be organized about it. Since Mercury orbits closer to the Sun than Earth, it's always located near the Sun in the sky. The only time to see Mercury is just before the Sun rises, or after it has set. You've got to have a clear view to the horizon to see the planet closest to the Sun.

And just in case you were wondering, the planet second closest to the Sun is Venus.

We have an extensive section just on Mercury on Universe Today. And did you know there's a spacecraft visiting Mercury called MESSENGER? You can read news about this mission here.

Here's a link to NASA's World Book on Mercury.

We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.

Filed under: Astronomy