Note:  Do not rely on this information. It is very old.

Mercury, in astronomy

Mercury, in astronomy, is the smallest planet, except the planetoids, in the solar system, and the one nearest the sun. It is never seen for more than two hours before sunrise or after sunset, and is not always visible then; but when it does appear, it is extremely brilliant. It was considered to have no spots on its surface, but the discovery of a very faint one during this century enabled the length of its day to be calculated as 24 hours 5 minutes. It takes 88 days to travel round the sun" its mean distance from that body being 35,000,000 miles. Even when it is most distant the sun appears four and a half times as big to it as it does to us, and when the two are at their nearest, this small planet gets ten times as much light and heat as we do. Forms of life, if any, must, therefore, be very different from the ones we know, unless the intense heat is tempered by an atmosphere of some kind. Mercury has no satellite, so its density has been calculated from its supposed effect on a passing comet. It is believed to be one-sixth greater than the density of the earth, and its gravity is supposed to be such that a pound would weigh about 7 oz. there, rendering motion of all kinds extremely easy. The diameter of Mercury is 3,060 miles, and its axis is by some supposed to be much inclined to the plane of its orbit. It is, however, sc small and difficult to observe, that comparatively little is known of it, its true shape, and the position of its axis, with its effects on its seasons being matters of conjecture only.