Moon back

from Wikipedia, the free encyclopedia
The back of the moon. This image is made up of individual photos from the years 2009 to 2011. The images were taken by the Lunar Reconnaissance Orbiter , a satellite orbiting the moon. At the top left the Mare Moscoviense , at the bottom left the dark Tsiolkovskiy crater , in the lower third of the image the spotty large basin region of Mare Ingenii , Leibnitz, Apollo and Poincaré.

The back of the moon is the hemisphere of the earth's moon that faces away from the earth and is therefore never visible. Strictly speaking, only 41 percent of the moon's surface is never visible from Earth. The reason is the lunar orbit inclined by 5 ° and its elliptical shape (see libration ).

The fact that the same half of the moon is always turned away from the earth has its cause in the bound rotation of the satellite - a phenomenon common in astronomy when two celestial bodies orbits closely . Due to the tidal force of the earth, the period of rotation of the moon has gradually adapted to the length of the month (29½ days, period of the moon phases).

Mankind has only known the appearance of the back of the moon since 1959, when a Soviet probe photographed this side. The following year the recordings were published in a lunar atlas. On January 3, 2019, 3:26 a.m.CET , the Chinese space probe Chang'e-4 landed for the first time on the back of the moon. The landing site was the Von Kármán crater in the South Pole Aitken Basin .

Differences to the visible half of the moon

The back of the moon was first explored at the end of 1959 by the Soviet lunar probe Lunik 3 , whose radio images captured 70 percent of the far side and offered a completely different view than the familiar and well-explored front of the moon. In particular, only a single dark plain ( Mare Moskwa ) was recognizable. The detection of the still uncharted territories succeeded in July 1965 after the flyby of the Soviet space probe Zond 3 , provided the first high-quality images of the far side of the moon. The Lunar Reconnaissance Orbiter of NASA has finally mapped in high resolution the back of 2010.

The three Apollo 8 crew members Frank Borman , James Lovell and William Anders were the first in 1968, and with twenty-one other Apollo astronauts, the only people to date who have seen the far side of the moon with their own eyes.

The topography of the front and back of the moon. The regional differences in altitude are much more pronounced on the latter .

Appearance

Even at first glance, it is noticeable that the dark areas, the lowlands ( mare ) covered by solidified lava , make up only a few percent of the surface, in contrast to about 30 percent on the side facing the earth. The rear side therefore has a higher reflectivity ( albedo ) on average ; so the back is brighter at a new moon than the front at a full moon.

The English-language term dark side of the moon is therefore all the more questionable . This does not mean a darkness, but the fact that this side was unknown to people for a long time.

There are also fewer moon mountains and ridges on the back than on the front. This is probably due to the few lunar seas or large impacts . The maximum difference in height between the deepest depressions in the South Pole Aitken Basin and the highest elevations in the neighboring east-central highlands with the Korolev and Hertzsprung craters is around 16 km. This is a few kilometers more than on the half of the moon facing the earth and only a little less than the 20 km on the surface of the earth's crust .

Geological background

The gravitational field on the front and back of the moon, red = greater, blue = lower gravity

From a geological - cosmogonic point of view, it is remarkable that the back of the moon has only four small lunar seas: the two relatively centrally located lowlands Mare Moscoviense and Mare Ingenii and the lowlands Mare Australe and Mare Orientale , which are visible at the edge in front of the front when there is extreme vibration . The back of the moon consists of more than 90 percent bright, crater-covered highlands.

The very dark floor of the large Tsiolkovskiy crater and the nearby Jules Verne crater is also striking . The South Pole Aitken Basin with a diameter of 2240 km is the largest impact crater on the Earth's moon. The two so dissimilar hemispheres also developed differently because the geometric center of the lunar sphere and its center of gravity are 1.8 kilometers (1 per thousand of the lunar radius) apart, which is related to an asymmetry of the inner structure and the lunar crust. According to a theory set up in 2011, the reason lies in a second earth satellite , which collided with the moon about 4.5 billion years ago.

GIF animation of a photo series of the transit of the Moon between the DSCOVR satellite , located at Lagrange point L 1 , and the Earth on July 16. It shows the back of the moon, which is otherwise invisible to us

Because of the lack of large lunar seas, which formed on the front about 4 billion years ago during the “ last great bombardment ”, there are no extensive lava layers on the back of the moon . In terms of larger mascons , mass or gravity anomalies as a result of large meteorite impacts, only the one under the Mare Orientale and the strongly indented basin region in the south should be mentioned; see picture on the right.

Space and astronomy plans

For some years now, astronomers have been discussing plans to use the back of the moon for particularly sensitive measurements. The advantage there is the freedom from any earthly interference light - which is also subject to the Hubble space telescope - and earthly radio traffic. However, it would be disadvantageous that telemetry and radio communications would only be possible via lunar satellites .

Because of the radiation and the temperatures, the proximity of a lunar pole would be advantageous as a location for such an observatory , where the monthly temperature differences are not more than 200 Kelvin as usual , but only a fraction of them. In 1994 the French astronomer Jean Heidmann (1923–2000) suggested the Saha lunar crater as the ideal location for a lunar radio telescope for SETI .

Moon back in fiction

  • In the science fiction drama Moon (2009), the sole operator of an automated conveyor system operated on the back of the moon finds out that he is just a clone .
  • In the comedy film Iron Sky (2012), the Nazi moon base Black Sun is on the back of the moon .

Back for other moons

The Planetary talks with some other moons in the solar system , the one to their planet tidal locking comprise of the "back side", averted or "outside". The bound rotation hits u. a. towards the four large moons of Jupiter and some moons of Saturn . Their hemispheres often have different crater densities from the early days, because the number of impacts is influenced by the orientation towards the planet. Statistically, most impacts are to be expected on that quarter of the moon that is on the outside but in front in the direction of movement.

Some moons also have two hemispheres of different brightness. This is particularly pronounced with Saturn's moon Japetus : the front half in the orbital sense has an albedo of only 0.04. This extremely dark region was named after the discoverer (1671) of the moon Cassini Regio and is likely covered with volcanic or meteoritic dust. The rear hemisphere is more than ten times as bright with an albedo of 0.5, similar to the surface of the great ice moons of Jupiter.

literature

  • Antonín Rükl : Moon - Mars - Venus. Pocket atlas of the closest celestial bodies . Prague 1977.
  • Josef Sadil : Focus on the moon , main chapter: " Selenography " , illustrated by Gerhard Pippig, Urania, Leipzig / Jena / Berlin 1962 (original title: Cíl měsíc , translated by Max A. Schönwälder), DNB 454251394 , OCLC 65043150 .
  • Chuck J. Byrne: The far side of the moon - a photographic guide . Springer, New York 2008, ISBN 978-0-387-73205-3

Web links

Individual evidence

  1. ↑ Successful first landing on the back of the moon , Tagesschau.de of January 3, 2019; accessed on January 3, 2019
  2. ↑ China successfully lands Chang'e-4 on far side of Moon on planetary.org , January 3, 2019; accessed on January 3, 2019
  3. ↑ High mountains, enigmatic trenches: The fascinating landscape of the moon. On: spiegel-online June 25, 2010.
  4. ^ Martin Jutzi, Erik Asphaug: Forming the lunar farside highlands by accretion of a companion moon . In: Nature . No. 476, August 2011, pp. 69-72. doi : 10.1038 / nature10289 .
  5. ↑ Jan Oliver Löfken: New evidence: Second moon once orbited the earth. weltderphysik.de, August 3, 2011, accessed April 18, 2015 .
  6. ^ Implications of the Lunar Mascon Discovery jstor.org, accessed March 11, 2011
  7. ^ Gregory A. Neumann, et al .: Seeing the Missing Half. Science February 13, 2009, Vol. 323 no. 5916 pp. 885-887, doi : 10.1126 / science.1170655 , abstract .
  8. ^ Jean Heidmann: A proposal for a radio frequency interference-free dedicated lunar far side crater for high sensitivity radio astronomy. Acta Astronautica, Vol. 46, Issue 8, 1 April 2000, pp. 555-558 doi : 10.1016 / S0094-5765 (00) 00002-3
  9. ↑ Claudio Maccone: LUNAR FARSIDE RADIO LAB @ setileague.org (PDF) ( Memento from June 25, 2012 in the Internet Archive ) (English)
  10. ^ J. Heidmann: Recent progress on the lunar farside crater Saha proposal. Acta Astronautica, Vol. 46, Issues 10-12, June 1, 2000, pp. 661-665, doi : 10.1016 / S0094-5765 (00) 00029-1
  11. ↑ Harald Zaun: SETI - the scientific search for extraterrestrial civilizations - opportunities, perspectives, risks. Heise, Hannover 2010, ISBN 978-3-936931-57-0 , p. 191.
  12. ↑ Patrick Moore et al .: Atlas of the Solar System , chapter on Jupiter and Saturn moons. Herder-Verlag, Freiburg-Vienna 1986