Mercury is the closest planet to the Sun. It averages about 36 million miles from it.
This figure is very much an average because interestingly, Mercury has a notably elliptical orbit. Its distance from the Sun varies from about 28 million miles at the closest, to about 43 million miles at furthest away.
Mercury
The proximity to the Sun has always made Mercury difficult to observe from Earth. You can never see it against a dark sky background. It is only visible for a few minutes before sunrise or after sunset.
Even when at the most favourable, it still appears close to the Sun in our sky. And in fact, astronomers had little information on the details of Mercury until the Mariner spacecraft photographed it in the mid-1970′s.
Another unusual aspect to the planet is that it rotates on its axis very slowly, taking nearly 59 Earth days to turn once. So the length of a Mercury day is 59 Earth days.
Mercury takes 88 Earth days to complete an orbit of the Sun, so there are less than two days in a year on Mercury! In fact there is almost an exact 3:2 relationship – 3 days every 2 years.
Cratered Mercury with volcanos (Messenger)
However, from the viewpoint of a fixed point on Mercury’s surface, the Sun would rise in the sky only once every 176 Earth days or once every 2 Mercury years.
The axis of Mercury is not tilted like the Earth, so there would be no seasonal effect.
The surface of Mercury is hard and rocky. There is little atmosphere and it suffers extremes of temperature between -180C and +470C.
All in all, Mercury is a very inhospitable place, by our standards.
