The mean distance from Mercury to the Sun is about 57 million km, or approximately 0.38 Astronomical Units or 3.2 light-minutes.
Light travels at a speed of 299,792 kilometers per second; 186,287 miles per second. It takes 499.0 seconds for light to travel from the Sun to the Earth, a distance called 1 Astronomical Unit.
The closest planet to the sun, Mercury takes the least time to orbit the giant star. Its close proximity boosts the world's temperature, and makes it difficult to hold on to its atmosphere. But just how close is close?
Mercury boasts an orbit that is the most elliptical of all of the planets, stretched out from a perfect circle. When it is closest to the sun, it is only 29 million miles (47 million km), but at its farthest, the distance to Mercury is 43 million miles (70 million km). (Pluto's orbit is even more eccentric, but Mercury holds the "most elliptical planetary orbit" since the far-flung body was downgraded to a dwarf planet; Pluto's downgrade also made Mercury the smallest of the eight remaining planets.)
This bizarre orbit confused early astronomers as they tried to piece together how the solar system worked. When Mercury is at its farthest from the sun, it is traveling the slowest. This gives Earth time to catch up to it about once every three and a half months.
Astronomers charting the motion of Mercury across the sky would see it moving backward over the course of several nights in relation to other stars in the sky. It wasn't until Nicolaus Copernicus established that planets traveled around the sun rather than around the Earth that the matter was cleared up.
Here are 10 things everyone should know about our solar system’s smallest planet shared by Solarsystem.nasa.gov.