(daily way in the model 4.2m)
Its diameter amounts to
4878 km and it is the innermost planet of our solar system. Mercury can approach
the sun on a relatively strong elliptical orbit up to 46 million km (0.31 AU)
and its distance is a maximum of 70 million km (0.47 AU) from it. Seen from the
earth, it never moves away from our central star more than 28° (about two spans)
and that's why it is only visible in the short time of dawn before sunrise or
after sunset. Because of the small distance to the sun, it has to move around
very fast according to the laws of Kepler in order not to fall onto it by the
force of gravity.
Its orbit speed, the highest of all planets, is averaging one and a half times
that of the earth and twice as fast as that of Mars. In 88 earth days Mercury
revolves around the sun on its declined orbit of 7°, which is the strongest
inclination to the ecliptic above all classical planets, whereby the sun's
rotating equator shows the same tilt as Mercury's orbit. Per each orbit round
the sun, the planet rotates 1 1/2 times around its own axis, meaning three
self-rotations in two Mercury years, which results in a strange effect : In any
place of the Mercury globe it takes 176 earth days from one sunrise to the next
one - which is according to one local solar day. So there a day is twice as long
as a year. With the help of the space shuttle Mariner 10 (1974) they were able
to gain the greatest amount of knowledge about Mercury.
Its
surface is, similar to the earth's moon's, strewn with craters and it has only a
thin remainder of atmosphere which mainly consists of helium. Because of the
long Mercury day the surface temperature varies from -183°C to +427°C.
The core of the planet, which is enclosed by a mantle of silicates, consists of
iron and nickel like that of the earth. Mercury has no moon, but a magnetic
field whose force only amounts to 1/100 of the value of the earth's. Because of
the small anomalies of the Mercury orbit, for a long time it was thought that
inside of its orbit could be a planet , which they named Vulcanus. With the help
of Einstein's theory of relativity, these divergences could be described,
though, as space curvature effect of the sun. Whereas the hypothetic planet
Vulcanus had not been found.
On May 7th 2003 the small Mercury globe will move exactly between earth
and sun and a tiny black point will adorn the sun`s disc : a Mercury transit !
Despite its short visibility, planet Mercury was already known in ancient Babylon (as Nabu), in Greece (as Hermes), in Egypt (as Thot) and in China , where it was called "hourstar", probably because of its velocity and fleetness. Most of the old astronomers had recognized and described that it moves around the sun in an orbit. As god Hermes (Greek) or Mercury (Roman) he was the mythical son of Zeus / Jupiter and the nymph of the mountains or Pleiade Maia.
As messenger of the gods he guided the dead into the underworld and was considered to be protector of the travellers and lucky charm for traders and thieves. It is also said that we owe the invention of writing and calculating to him. Like in the picture he is often shown with a winged cap, emissary rod and with winged sandals. When he was a child, Hermes/Mercury made a lyre out of a turtle (the constellation Lyre), which in the hands of his brother Apollo became his favourite instrument. Wednesday (German: Mittwoch, Italian: mercoledi, French: mercredi) is the day dedicated to Mercury. The term Wodan`s day for Wednesday shows that Mercury`s old-Nordic analogy was Wotan / Odin.
Picture: Statue of Hermes, winged messenger of the gods.