المعرفة

الجانب البعيد من القمر

إذا كنت تريد الفيلم الكندي-الفرنسي، انظر الجانب البعيد من القمر (فيلم). إذا كنت تريد استخدامات أخرى، انظر الجانب المظلم من القمر.

الجانب البعيد من القمر far side of the Moon، أو الجانب المظلم من القمر Dark side of the Moon، هو نصف القمر الذي دائماً لا يكون في مواجهة الأرض. تضاريس الجانب البعيد وعرة وتحتوي على العديد من الفوهات الصدمية ونسبة قليلة نسبياً من البحار القمرية. يحتوي القمر على واحدة من أكبر فوهات المجموعة الشمسية، حوض قطب-أتيكن الجنوبي. يتمتع جانبي القمر بأسبوعين من النهار تليها أسبوعين الليل؛ يسمى الجانب البعيد أحياناً "الجانب المظلم من القمر"، أي، الجانب الذي الغير مرئي وليس الجانب الذي يفتقد الضوء.[1][2][3][4]

الجانب البعيد من القمر، تصوير أپولو 16.

حوالي 18% من الجانب البعيد يمكن رؤيتها أحياناً من الأرض بسبب الميسان. الـ82% الباقية لم تُرصد حتى عام 1959، عندما صورها مسبار الفضاء لونا 3. نشرت الأكاديمية السوڤيتية للعلوم أول أطلس للجانب البعيد عام 1960. وكان رواد فضاء أپولو 8 أول بشر يرون الجانب المظلم بالعين المجردة عندما داروا حول القمر عام 1969. جميع عمليات الهبوط الناعم، سواء المأهولة أو الغير مأهولة، جرت على الجانب القريب من القمر، حتى 3 يناير 2019، عندما قامت مركبة الفضاء الصينية تشانگ-إ4 بأول هبوط على الجانب البعيد.[5]

يقترح علماء الفضاء تركيب تلسكوب راديوي ضخم على الجانب البعيد، حيث يمكنه حماية القمر من التداخل الراديوي المحتمل من الأرض.[6]

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تعريف

 
Due to tidal locking, the inhabitants of the central body (Earth) will never be able to see the satellite's (Moon) green area

Tidal forces from Earth have slowed the Moon's rotation to the point where the same side is always facing the Earth—a phenomenon called tidal locking. The other face, most of which is never visible from the Earth, is therefore called the "far side of the Moon". Over time, some crescent-shaped edges of the far side can be seen due to libration.[7] In total, 59 percent of the Moon's surface is visible from Earth at one time or another. Useful observation of the parts of the far side of the Moon occasionally visible from Earth is difficult because of the low viewing angle from Earth (they cannot be observed "full on").

A common misconception is that the Moon does not rotate on its axis. If that were so, the whole of the Moon would be visible to Earth over the course of its orbit. Instead, its rotation period matches its orbital period, meaning it turns around once for every orbit it makes: in Earth terms, it could be said that its day and its year have the same length (i.e., ~29.5 earth days).

The phrase "dark side of the Moon" does not refer to "dark" as in the absence of light, but rather "dark" as in unknown: until humans were able to send spacecraft around the Moon, this area had never been seen.[1][2][3] In reality, both the near and far sides receive (on average) almost equal amounts of light directly from the Sun. This symmetry is complicated by sunlight reflected from the Earth onto the near side (earthshine),[8] and by lunar eclipses, which occur only when the far side is already dark.

At night under a "full Earth" the near side of the Moon receives on the order of 10 lux of illumination (about what a city sidewalk under streetlights gets; this is 34 times more light than is received on Earth under a full Moon) whereas the dark side of the Moon during the lunar night receives only about 0.001 lux of starlight.[8] Only during a full Moon (as viewed from Earth) is the whole far side of the Moon dark.

The word dark has expanded to refer also to the fact that communication with spacecraft can be blocked while the spacecraft is on the far side of the Moon, during Apollo space missions for example.[9]


الاختلافات

انظر أيضاً: بحار القمر
 
صورة مفصلة من مدارية الاستطلاع القمري (LRO).
 
مرور القمر عبر الأرض كما يظهر من الساتل DSCOVR، حيث جانبه البعيد مرئي بالكامل.

يتميز كلا الجانبين بسمات مميزة، فيغطي الجانب القريب من القمر بعدد كبير من البحار القمرية. في حين تعرض الجانب البعيد للعديد من الاصطدامات بدلالة وجود عدد كبير من الفوهات الصدمية في حين أن عدد البحار القمرية قليل، ففقط 2.5% من سطح الجانب البعيد مغطى بالبحار القمرية،[10] بالمقارنة مع 31.2% من سطح الجانب القريب مغطى بالبحار القمرية. وأكثر تفسير مقبول لهذا التباين في التوزيع هو وجود كميات كبيرة من تركيز العناصر المنتجة للحرارة في الجانب القريب. وقد تم التأكد من هذا باستخدام مطياف أشعة گاما للمسبار لونار بروسبكتر. While other factors, such as surface elevation and crustal thickness, could also affect where basalts erupt, these do not explain why the far side South Pole–Aitken basin (which contains the lowest elevations of the Moon and possesses a thin crust) was not as volcanically active as Oceanus Procellarum on the near side.

It has also been proposed that the differences between the two hemispheres may have been caused by a collision with a smaller companion moon that also originated from the Theia collision.[11] In this model, the impact led to an accretionary pile rather than a crater, contributing a hemispheric layer of extent and thickness that may be consistent with the dimensions of the far side highlands. However, the chemical composition of the far side is inconsistent with this model.[بحاجة لمصدر]

The far side has more visible craters. This was thought to be a result of the effects of lunar lava flows, which cover and obscure craters, rather than a shielding effect from the Earth. NASA calculates that the Earth obscures only about 4 square degrees out of 41,000 square degrees of the sky as seen from the Moon. "This makes the Earth negligible as a shield for the Moon [and] it is likely that each side of the Moon has received equal numbers of impacts, but the resurfacing by lava results in fewer craters visible on the near side than the far side, even though both sides have received the same number of impacts."[12]

Newer research suggests that heat from Earth at the time when the Moon was formed is the reason the near side has fewer impact craters. The lunar crust consists primarily of plagioclases formed when aluminium and calcium condensed and combined with silicates in the mantle. The cooler far side experienced condensation of these elements sooner and so formed a thicker crust; meteoroid impacts on the near side would sometimes penetrate the thinner crust here and release basaltic lava that created the maria, but would rarely do so on the far side.[13]

 
صورة توضح الجانب البعيد من القمر (يسار) والجانب القريب من القمر (يمين).


الإستكشاف

الاستكشاف المبكر

 
7 أكتوبر، 1959، صورة التقطتها لونا 3 والتي أظهرت للبشر، لأول مرة، الجانب البعيد من القمر. Clearly visible is Mare Moscoviense (top right) and a mare triplet of Mare Crisium, Mare Marginis and Mare Smythii (left center).
 
When the first ever image of the far side of the Moon (A) is restored using advanced noise removal techniques (B) and compared to later LRO mission from NASA (C) the important feature points are distinctly visible and a clear, one to one mapping of the visible feature points are noticeable.

حتى أواخر 1950 كان معلومات قليلة جداً معروفة عن خصائص الجانب البعيد من القمر. فقد كانت ميسان القمر يسمح دورياً بلمحات محدود من ملامح طرف الجانب البعيد . كان ينظر لهذه الملامح من زاوية منخفضة، مما أعاق المراقبة المفيدة. (ثبت أن من الصعب التمييز بين حفرة من سلسلة جبال.) أما النسبة المتبقية 82٪ من السطح على الجانب الآخر فبقي مجهولا، وخضعت خصائصه إلى الكثير من التكهنات.

إحدى الأمثلة التي من الممكن رؤيتها من خلال ميسان القمر هو البحر الشرقي وهو حوض يمتد حوالي 1000 كم .

إلتقط المسبار لونا 3 في 7 أكتوبر 1959 أول صور للجانب البعيد من القمر،[14] وقد غطت هذه الصور ثلث سطح الجانب البعيد من القمر.[15] وقد صدر أول أطلس للجانب البعيد من القمر عن الأكاديمية السوفيتية للعلوم بعد أن تم تحليل هذه الصور في 6 نوفمبر 1960،[16] وقد شمل أكثر من 500 من ملامح الجانب البعيد ضمنه[17] وفي سنة 1965 قام مسبار سوفيتي آخر زوند 3 أرسل 25 صورة عالية الوضوح للجانب البعيد من القمر.[18] وصدر الجزء الثاني من الأطلس في موسكو سنة 1967.[19][20]

In 1961, the first globe (1:13600000 scale)[21] containing lunar features invisible from the Earth was released in the USSR, based on images from Luna 3.[22] On 20 July 1965, another Soviet probe, Zond 3, transmitted 25 pictures of very good quality of the lunar far side,[23] with much better resolution than those from Luna 3. In particular, they revealed chains of craters, hundreds of kilometers in length,[15] but, unexpectedly, no mare plains like those visible from Earth with the naked eye.[24]

In 1967, the second part of the Atlas of the Far Side of the Moon was published in Moscow,[25][26] based on data from Zond 3, with the catalog now including 4,000 newly discovered features of the lunar far side landscape.[15] In the same year, the first Complete Map of the Moon (1:5000000 scale[21]) and updated complete globe (1:10000000 scale), featuring 95 percent of the lunar surface,[21] were released in the Soviet Union.[27][28]

As many prominent landscape features of the far side were discovered by Soviet space probes, Soviet scientists selected names for them. This caused some controversy, and the International Astronomical Union, leaving many of those names intact, later assumed the role of naming lunar features on this hemisphere.

مهمة لمزيد من المسح

On 26 April 1962, NASA's Ranger 4 space probe became the first spacecraft to impact the far side of the Moon, although it failed to return any scientific data before impact.[29]

The first truly comprehensive and detailed mapping survey of the far side was undertaken by the American uncrewed Lunar Orbiter program launched by NASA from 1966 to 1967. Most of the coverage of the far side was provided by the final probe in the series, Lunar Orbiter 5.

أما أول رصد مباشر للجانب البعيد من القمر بالعين البشرية فكان سنة 1968 بواسطة رائدي فضاء البعثة أپولو 8.

“The backside looks like a sand pile my kids have played in for some time. It's all beat up, no definition, just a lot of bumps and holes.”

 
The far side of the Moon, with Mare Marginis and Mare Smythii visible, photographed by Apollo 16 in 1972. It is much more cratered than the near side of the Moon.

It has been seen by all 24 men who flew on Apollo 8 and Apollo 10 through Apollo 17, and photographed by multiple lunar probes. Spacecraft passing behind the Moon were out of direct radio communication with the Earth, and had to wait until the orbit allowed transmission. During the Apollo missions, the main engine of the Service Module was fired when the vessel was behind the Moon, producing some tense moments in Mission Control before the craft reappeared.

Geologist-astronaut Harrison Schmitt, who became the last to step onto the Moon, had aggressively lobbied for his landing site to be on the far side of the Moon, targeting the lava-filled crater Tsiolkovskiy. Schmitt's ambitious proposal included a special communications satellite based on the existing TIROS satellites to be launched into a Farquhar–Lissajous halo orbit around the L2 point so as to maintain line-of-sight contact with the astronauts during their powered descent and lunar surface operations. NASA administrators rejected these plans on the grounds of added risk and lack of funding.

The idea of utilizing Earth–Moon ل2 for communications satellite covering the Moon's far side has been realized, as China National Space Administration launched Queqiao relay satellite in 2018.[30] It has since been used for communications between the Chang'e 4 lander and Yutu 2 rover that have successfully landed in early 2019 on the lunar far side and ground stations on the Earth. And L2 is proposed to be "an ideal location" for a propellant depot as part of the proposed depot-based space transportation architecture.[31]

هبوط سلس

 
The Chang'e-4 lander imaged by the Yutu-2 rover on the lunar far side.

قامت المركبة الفضائية تشانگ-إ4 التابعة لإدارة الفضاء الوطنية الصينية في 3 يناير 2019 بأول هبوط ناعم على الجانب البعيد من القمر.[32]تتضمن المهمة مركبة هبوط مجهزة بمطياف راديوي منخفض التردد وأدوات بحث جيولوجي.[33]

In February 2020, Chinese astronomers reported, for the first time, a high-resolution image of a lunar ejecta sequence, and, as well, direct analysis of its internal architecture. These were based on observations made by the Lunar Penetrating Radar (LPR) on board the Yutu-2 rover.[34][35]

The Lunar Surface Electromagnetics Experiment (LuSEE-Night) lander, a mission to soft land as early as 2026 a robotic observatory on the far side designed to measure electromagnetic waves from the early history of the universe is being developed by NASA and the United States Department of Energy.[36]

 
The first panorama from the far side of the Moon taken by Chang'e 4


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الاستخدامات المحتملة والمهام

Because the far side of the Moon is shielded from radio transmissions from the Earth, it is considered a good location for placing radio telescopes for use by astronomers. Small, bowl-shaped craters provide a natural formation for a stationary telescope similar to Arecibo in Puerto Rico. For much larger-scale telescopes, the 100-kilometer-diameter (60 mi) crater Daedalus is situated near the center of the far side, and the 3-kilometer-high (2 mi) rim would help to block stray communications from orbiting satellites. Another potential candidate for a radio telescope is the Saha crater.[37]

Before deploying radio telescopes to the far side, several problems must be overcome. The fine lunar dust can contaminate equipment, vehicles, and space suits. The conducting materials used for the radio dishes must also be carefully shielded against the effects of solar flares. Finally, the area around the telescopes must be protected against contamination by other radio sources.

The ل2 Lagrange point of the Earth–Moon system is located about 62,800 km (39,000 mi) above the far side, which has also been proposed as a location for a future radio telescope which would perform a Lissajous orbit about the Lagrangian point.

One of the NASA missions to the Moon under study would send a sample-return lander to the South Pole–Aitken basin, the location of a major impact event that created a formation nearly 2,400 km (1,500 mi) across. The force of this impact has created a deep penetration into the lunar surface, and a sample returned from this site could be analyzed for information concerning the interior of the Moon.[38]

Because the near side is partly shielded from the solar wind by the Earth, the far side maria are expected to have the highest concentration of helium-3 on the surface of the Moon.[39] This isotope is relatively rare on the Earth, but has good potential for use as a fuel in fusion reactors. Proponents of lunar settlement have cited the presence of this material as a reason for developing a Moon base.[40]

الأطباق الطائرة المزعومة والمؤامرات

تضاريس مسماة

 
Some of the features of the geography of the far side of the Moon are labeled in this image

انظر أيضاً

المصادر

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  24. ^ خطأ استشهاد: وسم <ref> غير صحيح؛ لا نص تم توفيره للمراجع المسماة ley196604
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وصلات خارجية

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