Far side of the Moon

As the moon back those hemisphere of the Moon is called, which is not visible from Earth.

That one half of the moon is always facing away from the earth, has its cause in the bound rotation of the moon - a frequent phenomenon in astronomy at the close orbit two celestial bodies. Due to the tidal force of the Earth, the rotational period of the moon has gradually adapted the month length (29 ½ days, period of the phases of the moon ).

Strictly speaking, but only 41 % of the lunar surface are never visible. The reason is the 5 ° inclined lunar orbit and its elliptical shape (see libration ).

Differences to the visible moon half

The moon back was first explored by the Russian lunar probe Lunik 3 end of 1959, whose radio images 70 percent of the far side covered and a very different view offered than the usual, well-researched front of the moon.

The Lunar Reconnaissance Orbiter NASA has recently mapped the side of the moon in high resolution.

Appearance

Even at first glance striking that the dark areas covered by solidified lava plains ( Mare), only a few percent of the surface make up, as opposed to about 30 percent on the near side. Therefore, the back of the cut is a little lighter, it has a higher albedo. Probably as a result of the lack of lunar seas or large impacts exist also less mountains of the moon and grooves. The maximum height difference between the lowest valley and the highest authorities is - in the central highlands between Korolev and Hertzsprung, and mountains of eternal light near the south pole - about 16 km. These are a few miles over on the near half moon and only slightly less than the 20 km at the surface of the earth's crust.

Geological causes

From geological and cosmological vision is remarkable that the moon back has only four small lunar seas: the two relatively central lowlands Mare Moscoviense and Mare Ingenii and in extreme libration at the edge of the visible front of the front lowlands Mare Australe and Mare Orientale. The Moon is back to about 90 percent of light, crater -covered highlands. It is also noticeable the very dark floor of the large crater Tsiolkovskiy and the nearby crater Jules Verne. The South Pole - Aitken basin with a diameter of 2240 km is the largest impact crater on Earth's Moon. The two so unequal hemispheres have also be developed in different ways, that the geometric center of the Moon sphere and its center of gravity by 1.8 km ( 1 per thousand of the lunar radius) extending from each other, which is related to an asymmetry of the internal structure and the lunar crust.

Because of the lack of large lunar seas, which originated on the front about 4 billion years ago during the " last major bombing " can be found on the moon back no extensive lava flows. At larger mascons, mass or gravity anomalies as a result of large meteorite impacts, only that under the Mare Orientale and to mention the heavily indented pelvic region in the south; see picture on the right.

Astronautical astronomical plans

For several years, plans shall be considered by astronomers to use the moon back for sensitive measurements. The advantage is there in the freedom of any earthly stray light - which also about the Hubble Space Telescope subject - and of terrestrial radio communications. The disadvantage would be, however, that telemetry and radio communications would be possible only on lunar satellite.

Because of the radiation and the temperatures would be as the site of such an observatory near a Mondpols advantageous where the monthly temperature differences do not how else about 200 Kelvin, but only a fraction of that account. 1994 suggested the French astronomer Jean Heidmann ( 1923-2000 ) the lunar crater Saha as an ideal location for a lunar radio telescope for SETI ago.