Exploration of the Moon

Apollo 12 lunar module Intrepid prepares to descend towards the surface of the Moon. NASA photo.

The physical exploration of the Moon began when Luna 2, a space probe launched by the Soviet Union, made an impact on the surface of the Moon on September 14, 1959. Prior to that the only available means of exploration had been observation. The invention of the optical telescope brought about the first leap in the quality of lunar observations. Galileo Galilei is generally credited as the first person to use a telescope for astronomical purposes; having made his own telescope in 1609, the mountains and craters on the lunar surface were among his first observations using it.

In 1969, NASA's Project Apollo first successfully landed people on the Moon. They placed scientific experiments there and returned rocks and data that suggested the Moon is of a similar composition to the Earth.

Contents

Early history

In Mesopotamia, Babylonian astronomers by the early first millennium BC had discovered a repeating 18-year cycle of lunar eclipses. They had also known by this time that 19 solar years is about equal to 235 lunar months.[1] In the 2nd century BC, Seleucus of Seleucia correctly theorized that tides were caused by the Moon, although he believed that the interaction was mediated by the Earth's atmosphere. According to Strabo (1.1.9), Seleucus was the first to state that the tides are due to the attraction of the Moon, and that the height of the tides depends on the Moon's position relative to the Sun.[2]

By the mid-first millennium BC, Indian astronomers described the Moon’s monthly elongation in the Aitareya Brāhmana.[3] By 499 AD, the Indian astronomer Aryabhata mentioned in his Aryabhatiya that reflected sunlight is the cause behind the shining of the moon.[4]

Among the first in the Western world to offer a scientific explanation for the Moon was the Greek philosopher Anaxagoras (d. 428 BC), who reasoned that the Sun and Moon were both giant spherical rocks, and that the latter reflected the light of the former. His atheistic view of the heavens was one cause for his imprisonment and eventual exile.[5] In Aristotle's (384–322 BC) description of the universe, the Moon marked the boundary between the spheres of the mutable elements (earth, water, air and fire), and the imperishable stars of aether. This separation was held to be part of Aristotelian physics for many centuries after.[6] In the philosophy of Aristotle, the heavens, starting at the Moon, were the realm of perfection, the sublunary region was the realm of change and corruption, and any resemblance between these regions was strictly ruled out. Aristotle himself suggested that the Moon partook perhaps of some contamination from the realm of corruption.[7] In his little book On the Face in the Moon's Orb, Plutarch expressed rather different views on the relationship between the Moon and Earth. He suggested that the Moon had deep recesses in which the light of the Sun did not reach and that the spots are nothing but the shadows of rivers or deep chasms. He also entertained the possibility that the Moon was inhabited. It had been suggested already in antiquity that the Moon was a perfect mirror and that its markings were reflections of earthly features, but this explanation was easily dismissed because the face of the Moon never changes as it moves about the Earth.[7] The explanation that finally became standard was that there were variations of "density" in the Moon that caused this otherwise perfectly spherical body to appear the way it does.[7] The perfection of the Moon, and therefore the heavens, was thus preserved. Aristarchus went a step further and computed the distance from Earth, together with its size, obtaining a value of 20 times the Earth radius for the distance (the real value is 60; the Earth radius was roughly known since Eratosthenes).

During the Warring States of China, astronomer Shi Shen (fl. 4th century BC) gave instructions for predicting solar and lunar eclipses based on the relative positions of the Moon and Sun.[8] Although the Chinese of the Han Dynasty (202 BC–202 AD) believed the Moon to be energy equated to qi, their 'radiating influence' theory recognized that the light of the Moon was merely a reflection of the Sun (mentioned by Anaxagoras above).[9] This was supported by mainstream thinkers such as Jing Fang (78–37 BC) and Zhang Heng (78–139 AD), but it was also opposed by the influential philosopher Wang Chong (27–97 AD).[9] Jing Fang noted the sphericity of the Moon, while Zhang Heng accurately described a lunar eclipse and solar eclipse.[9][10] These assertions were supported by Shen Kuo (1031–1095) of the Song Dynasty (960–1279) who created an allegory equating the waxing and waning of the Moon to a round ball of reflective silver that, when doused with white powder and viewed from the side, would appear to be a crescent.[11] He also noted that the reason for the Sun and Moon not eclipsing every time their paths met was because of a small obliquity in their orbital paths.[11]

Habash al-Hasib al-Marwazi, a Persian astronomer, conducted various observations at the Al-Shammisiyyah observatory in Baghdad between 825 and 835 AD.[12] Using these observations, he estimated the Moon's diameter as 3,037 km (equivalent to 1,519 km radius) and its distance from the Earth as 215,209 miles, which come close to the currently accepted values.[13] In 1021, the Islamic physicist, Alhazen, accurately explained the Moon illusion in the Book of Optics, which stated that judging the distance of an object depends on there being an uninterrupted sequence of intervening bodies between the object and the observer. With the Moon, there are no intervening objects, therefore since the size of an object depends on its observed distance, which is in this case inaccurate, the Moon appears larger on the horizon. Through Alhazen's work, the Moon illusion gradually came to be accepted as a psychological phenomenon.[14] He also investigated moonlight, which he proved through experimentation that it originates from sunlight and correctly concluded that it "emits light from those portions of its surface which the sun's light strikes."[15]

By the Middle Ages, before the invention of the telescope, an increasing number of people began to recognise the Moon as a sphere, though many believed that it was "perfectly smooth".[16] In 1609, Galileo Galilei drew one of the first telescopic drawings of the Moon in his book Sidereus Nuncius and noted that it was not smooth but had mountains and craters. Later in the 17th century, Giovanni Battista Riccioli and Francesco Maria Grimaldi drew a map of the Moon and gave many craters the names they still have today. On maps, the dark parts of the Moon's surface were called maria (singular mare) or seas, and the light parts were called terrae or continents.

The medieval followers of Aristotle, in the Islamic world and then in Christian Europe, tried to make sense of the lunar spots in Aristotelian terms.[7] Thomas Harriot, as well as Galilei, drew the first telescopic representation of the Moon and observed it for several years. His drawings, however, remained unpublished.[7] The first map of the Moon was made by the Belgian cosmographer and astronomer Michael Florent van Langren in 1645.[7] Two years later a much more influential effort was published by Johannes Hevelius. In 1647 Hevelius published Selenographia, the first treatise entirely devoted to the Moon. Hevelius's nomenclature, although used in Protestant countries until the eighteenth century, was replaced by the system published in 1651 by the Jesuit astronomer Giovanni Battista Riccioli, who gave the large naked-eye spots the names of seas and the telescopic spots (now called craters) the name of philosophers and astronomers.[7] In 1753 the Croatian Jesuit and astronomer Roger Joseph Boscovich discovered the absence of atmosphere on the Moon. In 1824 Franz von Gruithuisen explained the formation of craters as a result of meteorite strikes.[17]

The possibility that the Moon contains vegetation and is inhabited by selenites was seriously considered by major astronomers even into the first decades of the 19th century. The contrast between the brighter highlands and darker maria create the patterns seen by different cultures as the Man in the Moon, the rabbit and the buffalo, among others. In 1835, the Great Moon Hoax fooled some people into thinking that there were exotic animals living on the Moon.[18] Almost at the same time however (during 1834–1836), Wilhelm Beer and Johann Heinrich Mädler were publishing their four-volume Mappa Selenographica and the book Der Mond in 1837, which firmly established the conclusion that the Moon has no bodies of water nor any appreciable atmosphere.

Space race

Main article: Space race
Lunokhod 1

The Cold War-inspired space race between the Soviet Union and the United States of America accelerated with a focus on the Moon. This included many scientifically important firsts, such as the first photographs of the then-unseen far side of the Moon in 1959 by the Soviet Union, and culminated with the landing of the first humans on the Moon in 1969, widely seen around the world as one of the pivotal events of the 20th century, and indeed of human history in general.

Landing map of Apollo, Surveyor and Luna missions.
Apollo 17 astronaut Harrison Schmitt standing next to a boulder at Taurus-Littrow during the third EVA (extravehicular activity). NASA photo.

The first man-made object to reach the Moon was the unmanned Soviet probe Luna 2, which made a hard landing on September 14, 1959, at 21:02:24 Z. The far side of the Moon was first photographed on October 7, 1959 by the Soviet probe Luna 3. In an effort to compete with these Soviet successes, U.S. President John F. Kennedy proposed the national goal of landing a man on the Moon. Speaking to a Joint Session of Congress on May 25, 1961, he said

"First, I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space."[19]

The Soviets nonetheless remained in the lead for some time. Luna 9 was the first probe to soft land on the Moon and transmit pictures from the Lunar surface on February 3, 1966. It was proven that a lunar lander would not sink into a thick layer of dust, as had been feared. The first artificial satellite of the Moon was the Soviet probe Luna 10 (launched March 31, 1966). One of the main impediments to human exploration of the Moon was development of adequate heat shield technology to permit atmospheric re-entry without completely burning up a manned spacecraft. The U.S. gained early supremacy in this field through NASA research in thermogravimetric experiments in hypersonic wind tunnels.

On December 24, 1968, the crew of Apollo 8, Frank Borman, James Lovell and William Anders, became the first human beings to enter lunar orbit and see the far side of the Moon with their own eyes. Humans first landed on the Moon on July 20, 1969. The first man to walk on the lunar surface was Neil Armstrong, commander of the U.S. mission Apollo 11. The first robot lunar rover to land on the Moon was the Soviet vessel Lunokhod 1 on November 17, 1970 as part of the Lunokhod program. To date, the last man to stand on the Moon was Eugene Cernan, who as part of the mission Apollo 17 walked on the Moon in December 1972. See also: A full list of lunar Apollo astronauts.

Moon rock samples were brought back to Earth by three Luna missions (Luna 16, 20, and 24) and the Apollo missions 11 through 17 (excepting Apollo 13, which aborted its planned lunar landing).

From the mid-1960s to the mid-1970s there were 65 Moon landings (with 10 in 1971 alone), but after Luna 24 in 1976 they suddenly stopped. The Soviet Union started focusing on Venus and space stations and the U.S. on Mars and beyond.

Recent exploration

In 1990 Japan visited the Moon with the Hiten spacecraft, becoming the third country to place an object in orbit around the Moon. The spacecraft released the Hagoromo probe into lunar orbit, but the transmitter failed, thereby preventing further scientific use of the mission. In September 2007, Japan launched the SELENE spacecraft, with the objectives "to obtain scientific data of the lunar origin and evolution and to develop the technology for the future lunar exploration", according to the JAXA official website.[20]

NASA launched the Clementine mission in 1994, and Lunar Prospector in 1998.

The European Space Agency launched a small, low-cost lunar orbital probe called SMART 1 on September 27, 2003. SMART 1's primary goal was to take three-dimensional X-ray and infrared imagery of the lunar surface. SMART 1 entered lunar orbit on November 15, 2004 and continued to make observations until September 3, 2006, when it was intentionally crashed into the lunar surface in order to study the impact plume.[21]

The People's Republic of China has begun the Chang'e program for exploring the Moon and is investigating the prospect of lunar mining, specifically looking for the isotope helium-3 for use as an energy source on Earth.[22] China launched the Chang'e 1 robotic lunar orbiter on October 24, 2007. Originally planned for a one-year mission, the Chang'e 1 mission was very successful and ended up being extended for another four months. On March 1, 2009, Chang'e 1 was intentionally impacted on the lunar surface completing the 16 month mission.

India's national space agency, Indian Space Research Organization (ISRO), launched Chandrayaan-1, an unmanned lunar orbiter, on October 22, 2008.[23] The lunar probe was originally intended to orbit the Moon for two years, with scientific objectives to prepare a three-dimensional atlas of the near and far side of the Moon and to conduct a chemical and mineralogical mapping of the lunar surface.[24][25] The unmanned Moon Impact Probe landed on the Moon at 15:04 GMT on November 14, 2008 [26] making India the fourth country to touch down on the lunar surface. Among its many achievements was the discovery of the widespread presence of water molecules in lunar soil.[27]

NASA launched a preliminary unmanned mission, the Lunar Reconnaissance Orbiter, on June 18, 2009. LRO will take high resolution imagery of the Moon's surface and carries the Lunar Crater Observation and Sensing Satellite (LCROSS), which will investigate the possible existence of water in Shackleton crater.

Future plans

The planned NASA Lunar Reconnaissance Orbiter

On January 14, 2004, US President George W. Bush announced the Vision for Space Exploration, a plan leading to new manned lunar missions by 2020. NASA's plan to accomplish that goal was announced on March 19, 2005,[28] and was promptly dubbed "Apollo 2.0" by critics.

China plans to launch the Chang'e 2 lunar orbiter in October 2010. It also plan to land the rover Chang'e 3 on the Moon in 2013, and to conduct a sample return mission in 2017.

India expects to launch another indigenous lunar mission by 2013 which would place a motorized rover on the surface of the Moon.[29]

Japanese Aerospace Exploration Agency (JAXA) plans a manned lunar landing around 2020 that would lead to a manned lunar base by 2030; however, there is no budget yet for this project. This is highly unlikely to happen.[30]

Russia also announced to resume its previously frozen project Luna-Glob, an unmanned lander and orbiter, which is slated to launch in 2012.[31]

Germany also announced in March 2007 that it will launch a national lunar orbiter, LEO in 2012.[32] however the mission was cancelled due to budgetary constraints.[33]

In August 2007, NASA stated that all future missions and explorations of the Moon will be done entirely using the metric system. This was done to improve cooperation with space agencies of other countries which already use the metric system.[34]

The European Space Agency has also announced its intention to send a manned mission to the Moon, as part of the Aurora programme.

On September 13, 2007, the X Prize Foundation, in concert with Google, Inc., announced the Google Lunar X Prize. This contest requires competitors "to land a privately funded robotic rover on the Moon that is capable of completing several mission objectives, including roaming the lunar surface for at least 500 meters and sending video, images and data back to the Earth."[35]

See also

References

  1. ↑ A. Aaboe, J. P. Britton, J. A. Henderson, Otto Neugebauer, A. J. Sachs (1991), "Saros Cycle Dates and Related Babylonian Astronomical Texts", Transactions of the American Philosophical Society (American Philosophical Society) 81 (6): 1–75, http://www.jstor.org/stable/1006543, retrieved 2010-04-08, "One comprises what we have called "Saros Cycle Texts," which give the months of eclipse possibilities arranged in consistent cycles of 223 months (or 18 years)." 
  2. ↑ van der Waerden, Bartel Leendert (1987). "The Heliocentric System in Greek, Persian and Hindu Astronomy". Annals of the New York Academy of Sciences 500: 1. PMID 3296915. 
  3. ↑ Sarma (2008), Astronomy in India
  4. ↑ Hayashi (2008), Aryabhata I
  5. ↑ O'Connor, J.J.; Robertson, E.F. (February 1999). "Anaxagoras of Clazomenae". University of St Andrews. http://www-history.mcs.st-andrews.ac.uk/Biographies/Anaxagoras.html. Retrieved 2007-04-12. 
  6. ↑ Lewis, C. S. (1964). The Discarded Image. Cambridge: Cambridge University Press. pp. 108. ISBN 0-521047735-2. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 "The Galileo Project". http://galileo.rice.edu/sci/observations/Moon.html. Retrieved 2007-09-14. 
  8. ↑ Needham, Joseph (1986). Science and Civilization in China. 3, Mathematics and the Sciences of the Heavens and Earth. Taipei: Caves Books. p. 411. ISBN 0-521058015. 
  9. ↑ 9.0 9.1 9.2 Needham, Joseph (1986). Science and Civilization in China. 3, Mathematics and the Sciences of the Heavens and Earth. Taipei: Caves Books. pp. 413–414. ISBN 0-521058015. 
  10. ↑ Needham, Joseph (1986). Science and Civilization in China. 3, Mathematics and the Sciences of the Heavens and Earth. Taipei: Caves Books. p. 227. ISBN 0-521058015. 
  11. ↑ 11.0 11.1 Needham, Joseph (1986). Science and Civilization in China. 3, Mathematics and the Sciences of the Heavens and Earth. Taipei: Caves Books. pp. 415–416. ISBN 0-521058015. 
  12. ↑ Langermann, Y. Tzvi (1985). "The Book of Bodies and Distances of Habash al-Hasib". Centaurus 28: 108–128 [112]. doi:10.1111/j.1600-0498.1985.tb00831.x. 
  13. ↑ Langermann, Y. Tzvi (1985). "The Book of Bodies and Distances of Habash al-Hasib". Centaurus 28: 108–128 [111]. doi:10.1111/j.1600-0498.1985.tb00831.x. 
  14. ↑ Hershenson, Maurice (1989). The Moon illusion. Routledge. pp. 9–10. ISBN 9780805801217. 
  15. ↑ Toomer, G. J. (December 1964). "Review: Ibn al-Haythams Weg zur Physik by Matthias Schramm". Isis 55 (4): 463–465. doi:10.1086/349914. 
  16. ↑ Van Helden, A. (1995). "The Moon". Galileo Project. http://galileo.rice.edu/sci/observations/moon.html. Retrieved 2007-04-12. 
  17. ↑ Энциклопедия для детей (астрономия). Москва: Аванта+. 1998. ISBN 5-89501-016-4. 
  18. ↑ Boese, A. (2002). "The Great Moon Hoax". Museum of Hoaxes. http://www.museumofhoaxes.com/moonhoax.html. Retrieved 2007-04-12. 
  19. ↑ Special Message to the Congress on Urgent National Needs Page 4 - John F. Kennedy Presidential Library & Museum
  20. ↑ "Kaguya (SELENE)". JAXA. http://www.selene.jaxa.jp/index_e.htm. Retrieved 2007-06-25. 
  21. ↑ "SMART-1 Impacts Moon". ESA. 4 September 2006. http://www.esa.int/esaCP/SEMBY5BVLRE_index_0.html. Retrieved 2006-09-03. 
  22. ↑ David, Leonard (04 March 2003). "China Outlines its Lunar Ambitions". Space.com. http://space.com/missionlaunches/china_Moon_030304.html. Retrieved 2006-03-20. 
  23. ↑ http://www.ndtv.com/convergence/ndtv/Moonmission/Election_Story.aspx?id=NEWEN20080069654
  24. ↑ "Chandrayaan-1 Scientific Objectives". Indian Space Research Organisation. http://www.isro.org/chandrayaan/htmls/objective_scientific.htm. 
  25. ↑ http://www.deccanherald.com/CONTENT/Sep192008/national2008091890838.asp
  26. ↑ "India sends probe on to the Moon". BBC. November 14, 2008. http://news.bbc.co.uk/2/hi/south_asia/7730157.stm. Retrieved 2008-11-16. 
  27. ↑ Lunar Missions Detect Water on Moon
  28. ↑ "How We'll Get Back to the Moon". NASA. http://www.nasa.gov/missions/solarsystem/cev.html. Retrieved 2006-03-20. 
  29. ↑ Staff Writers (2004-11-04). "Competition heating up for Moon exploration". IOL. http://www.iol.co.za/index.php?set_id=1&click_id=31&art_id=qw1101276721575B253. Retrieved 2008-01-25. 
  30. ↑ Staff Writers (2006-08-03). "Japan Plans Moon Base By 2030". Moon Daily. SpaceDaily. http://www.Moondaily.com/reports/Japan_Plans_Moon_Base_By_2030_999.html. Retrieved 2006-11-17. 
  31. ↑ Covault, Craig (2006-06-04). "Russia Plans Ambitious Robotic Lunar Mission". http://www.aviationnow.com/avnow/news/channel_awst_story.jsp?id=news/aw060506p2.xml. 
  32. ↑ news, Spiegel (2007-02-28). "Germany plans own Moon mission". http://www.spiegel.de/wissenschaft/weltall/0,1518,469219,00.html. 
  33. ↑ [1]
  34. ↑ NASA - Metric Moon
  35. ↑ "Google Sponsors Lunar X PRIZE to Create a Space Race for a New Generation". X PRIZE Foundation. http://www.googlelunarxprize.org/lunar/press-release/google-sponsors-lunar-x-prize-to-create-a-space-race-for-a-new-generation. Retrieved 2007-09-13. 

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