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Home , Collision, Geology of the Moon, Rotation period

www.onthemoonagain.org GET YOUR TELESCOPE OUT TO SHARE THE

SEE YOU ON JULY 12 AND 13, 2019 I F R E H C

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Septembre 2011 – l’ ASTRONOMIE - 1 General presentation of the Moon The Moon is the only natural of the . With a diameter of 3474 km, its ave - rage distance from the Earth is 381500 km. The Moon is the first and, to this , the only non-terrestrial planetary body visited by Mankind. The first to be there was the American astronaut Neil Armstrong on July 21, 1969, 50 ago. After him, eleven other men walked on the Moon, all be part of the Apollo space program. Observation conditions on July 12/13

On July 12 and 13, 2019, the Moon is gibbous increasing (the occurring on July 16, 2019). Not far from the Moon, towards the South, one will find without diffi - culty the . The planet is a little further away.

The Moon in Paris on July 12, 2019 The Moon in Paris on July 13, 2019 The Earth-Moon couple The Earth-Moon couple is extremely complex. It depends on many astrophysical factors. Thus, the Earth performs a turn on itself in 23 hours 56 minutes and 4.1 , and revolves around the in 365256 days at an average distance of 149597870 kilometers. Its mass is 5.95 10 24 kg and its diameter of 12846 km. Its around the Sun is almost cir - cular (the eccentricity of the latter being very weak). The Moon is 27322 days to accomplish a revolution around the Earth: it is the sidereal lunar , in other words the time taken to perform a complete revolution and thus find the same position with respect to the . The duration of the synodic month (the time taken to find the same position of the Earth- Moon axis with respect to the Sun), and which separates two new , is 29,531 days. This is the current duration that is used to express the lunar cycle. The lunar orbit is an ellipse of "mean radius" 384392 km, which varies between 356410 km at the perigee (clo - sest point of the Earth) and 406.680 km at the apogee (point furthest from the Earth). The mass of the Moon is 7.35 10 22 kg and its diameter is 3472 km. The Sun has an equato - rial diameter of 1392000 km and a mass = 1,99 10 30 kg. While performing an entire revolu - tion around the Earth (the sidereal month), the Moon performs exactly one rotation on itself, which is why the Moon always presents the same face to the Earth. This phenome - non is known as "synchronous" rotation. It was the tidal effect (terrestrial and oceanic) that gradually stabilized the Moon in this position. The Earth and the Moon describe an orbit around a common center of mass located in the Earth's depths. The barycenter of this cou - ple is about 4650 km from the center of the Earth. I F R E H C

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Septembre 2011 – l’ ASTRONOMIE - 3

History of the formation o try to explain s have been developed t theories and hypothese turn Many pollo missions and the re of the Moon. Since the A the formation hared by the scientific h, the hypothesis most s of samples on the Eart h and a pla- between the young Eart nity is that of a collision commu rs named . This otoplanet) the size of Ma netoid body (pr er the birth of the rred 100 million years aft would have occu pothesis billion years ago. This hy tem, that is to say 4,468 solar sys the material ejected by e Moon was created from proposes that th de up of "re-arran- oon would be largely ma the collision. Thus, the M ged" terrestrial matter. The geology of the moon is a geology very different from that of the Earth. Since the moon has no , hydrosphere or biosphere, due to meteorological phe - nomena is absent. Plate , as we know it on Earth, has no equivalent; the is low and its soil cools faster because of the absence of atmosphere playing a buffer role thermo-regulator. Like the Earth, the Moon is a differentiated , with a , a and a nucleus. The lunar surface results from a complex combining different processes, such as meteoritic impacts and . The geo - logical studies of the Moon are based on the combination of telescopic observations from the Earth, measurements in orbit by automatic spacecraft, analyzes of lunar samples and geophysical data. Six landing sites were visited during the missions between 1969 and 1972. The astronauts were able to bring back about 385 kg of lunar rocks, most of which have been stored since 1979 at the Lunar Sample Laboratory Facility in Houston. In addition, three missions of the Soviet Union via the automa - tic program Luna also allowed the return of some 326 gr of on Earth. The Moon is the only extraterrestrial body for which humans have samples whose geological origin is known. However, several questions about the geological characteristics of the Moon remain unanswered.

Apollo Missions The Apollo program is NASA's To reach the Moon, the leaders intended for landing on the space program during the period finally rallied to the audacious Moon. The giant 3,000-ton Saturn 1961-1975, which allowed the method of rendezvous in lunar V , capable of 140 tons of United States to send men to the orbit, which required to have two low orbit, was developed to moon for the first time. It was spacecraft whose lunar module launch the lunar expedition vehi - launched by President John F. cles. The program will draw a Kennedy on May 25, 1961, prima - considerable budget (US $ 169 bil - rily to regain the American pres - lion current) and mobilize up to tige undermined by the suc - 400,000 people. Two serious cesses of Soviet astronau - accidents occurred during tics, at a time when the the project: the ground cold war between the fire of the Apollo 1 spa - two superpowers was cecraft whose crew in full swing. perished burned and The goal of the pro - which resulted in a gram was to put a delay of nearly two man on the moon years in the calendar before the end of the and the explosion of decade. On 21 July an tank of the 1969, this objective vessel spa - was achieved by two cecraft whose crew of the three crew mem - survived using the lunar bers of the mis - module as a rescue ship. sion, Neil Armstrong and Buzz Aldrin. Five other mis - sions subsequently landed on other lunar sites and stayed there for up to three days. These expe - ditions yielded 385 kg of lunar rock and set up several batteries issions Luna of scientific instruments. The The Soviet m by the Soviet Union to the The Luna automatic program includes all space missions launched astronauts made in-situ observa - ially part of this program but Moon between 1959 and 1976. Twenty-four space probes are offic goals. From the beginning, tions during lunar ground excur - there were in fact 45 in all. Fifteen of these missions achieved their Soviet know-how over that of sions of up to eight hours, assis - political considerations aimed at demonstrating the superiority of nges of the space race disap- ted from by an all-ter - the United States prevailed over scientific motives. When the challe ited States directs its Exploration program mainly to rain vehicle, the . pear, the Luna program ends while the Un and the outer of the solar system. n space exploration. Luna 1, No American orbital flights had The Luna program is at the origin of many of the first techniques i a 2 (1959) is the first artificial yet been made in May 1961. To launched in 1959, is the first spacecraft to break ground while Lun ph of the hidden side of the fulfill the goal set by the presi - object to reach the lunar ground. Luna 3 makes the first photogra the Moon, while Luna 16 Moon (1959). Luna 9 (1966) is the first probe to smoothly on dent, NASA launched several pro - una 17 (1970) and 21 (1973) (1970) is the first robot to bring a lunar sample back to Earth.The L l tens of kilometers on the sur- grams to prepare future lunar missions carry the first astromobiles (rovers) that will cover severa questions remain unanswe- expeditions: the Gemini program face of the Moon. On the scientific side, although many important terpart programs (Surveyor to develop space flight tech - red at the end of the program, the Luna program, like the US coun advanced our knowledge of and Lunar Orbiter Program and the Apollo program) have greatly niques and reconnaissance pro - n face of the Moon, lunar gra- the Moon: composition of the lunar soil, topography of the hidde s and radiation levels ... grams (Surveyor program, Ranger vitational field, evolution of the Earth-Moon distance, temperature pactor, orbiter, landing gear, ...) to, among other things, map The program has implemented space probes of different types (im as the program progresses, the landing zones and determine rover, return of sample). These are becoming more sophisticated the last orbiter. Several laun- with a growing weight of 361 kg to almost 6 tonnes for rovers and the consistency of the lunar soil. hat are causing a lot of the fai- chers have been used but all have suffered from reliability issues t ram in 1976, the Soviet Union lures of the Luna missions. Since the last mission of the Luna prog have no longer launched a and Russia (which has taken over from the ) probe to the moon. Frames face of the Moon. Although the scien- two bodies would thus have mixed Apollo 11 tific objective of Apollo 11 was limited together to a large extent, with part Apollo 11 is a mission of the American by the length of stay on the moon of Theia ending at the centre of the Space Program Apollo during which, and the reduced carrying capacity of Earth, and the rest orbiting around it for the first time in history, men lan- the spacecraft used, the mission pro- to coalesce and form the Moon. This ded on the Moon, July 20, 1969 (9:56 vides important results. Its unfolding, model, formulated in 1975 by the pm in Houston). NASA fulfills the goal especially the first steps on the Moon young astronomers W. K. Hartmann set by President Kennedy. This chal- filmed by a video camera and broad- and D. R. Davis, is the one which best lenge is launched while NASA has not cast live, constitute an event followed explains the various properties of yet put into orbit a single astronaut. on the planet globally by hundreds of lunar rocks, such as their chemistry The project succeeds thanks to the millions of people. low in volatile elements, as well as the mobilization of considerable human very small size of the Moon's core and financial resources. determined by Apollo 11 is the culmination of a Lunar samples deployed by astronauts (only 1% of series of missions that allow the deve- The Apollo and Luna missions, and in the Moon's volume, while the Earth's lopment of the necessary space tech- particular the samples they brought core accounts for 15% of the planet's niques, spacecraft and a giant laun- back, have changed our understan- volume). cher as well as the recognition of lan- ding of the genesis of the Moon and ding sites on the Moon. This is the planets... First of all, they made us third mission to approach the Moon, understand that the craters that The far side after and , and the sculpt the surface of our satellite are The is the hemis- fifth crewed mission of the Apollo the scars of collisions with other pla- phere of the Moon which is perma- program. The spacecraft carrying the netary bodies, and not the craters nently on the opposite side of the crew is launched from the Kennedy through which the of huge volca- Earth, the other being called the visi- Space Center on July 16, 1969 by the noes flowed. These cosmic scars are ble face or the . giant rocket Saturn V developed for visible at all scales, from the hundreds Indeed, a single hemisphere of the this program. She takes Neil of kilometres of large lunar basins to Moon is visible from Earth, because Armstrong, Mission Commander and the signs of crushing in the rocks, and the Moon has a rotation period equal Lunar Module Pilot, Buzz Aldrin, who to the very fine dust that forms the to its period of revolution (27.3217 accompanies Armstrong to the lunar soil. This dust is produced by what is days), phenomenon called synchro- ground, and Michael Collins, pilot of called "impact gardening", i.e. the nous rotation. The other hemisphere the command and service module hypervelocity impacts of objects, is therefore invisible from Earth, and that will remain in lunar orbit. where even the smallest ones reach was photographed and mapped only Armstrong and Aldrin spend 21 hours the ground of this atmosphere-free thanks to the space probes, the first and 36 minutes on the surface of the body. Impacts are now understood as being the Soviet Luna 3 probe in moon and perform a unique space- a major geological phenomenon at 1959. The first men to see it directly walk with a duration of 2 hours and the scale of the Solar System: the end were the crew of the Apollo 8 mission 31 minutes. After taking off again and of the construction of planetary orbiting the moon in 1968. The rough making an appointment in lunar orbit bodies by the process of "accretion", terrain is remarkable both for the with the command and service i.e. the accumulation of smaller multitude of craters and for its module, the Apollo spacecraft bodies as a result of collisions. The poverty in the lunar . This hidden resumes the path of the Earth and Moon itself is considered to be the face also has the largest known landed without incident in the Pacific result of a "giant impact": the collision of the solar system: the Ocean at the end of a flight that will of the Earth with Theia, a body the South Pole-Aitken basin. It was envi- have lasted 8 days, 3 hours and 18 size of Mars. This collision would have saged to install gigantic radio teles- minutes. caused the fusion and evaporation of copes, with the advantage that they During this mission, 21.7 kg of lunar Theia and a of large part of the Earth, would be protected from possible soil is collected and several scientific forming a very hot object rotating on radio interference from the Earth. instruments are installed on the sur- itself: a "synestia". The materials of the on the moon n. Liquid water can not There is water on the moo water vapor is decom- persist on the surface and ulting being posed by sunlight, the res ever, the presence of rapidly lost in space. How he permanent sha- water ice is envisaged in t since the 1960s. dow of polar o been detected in Water molecules have als . Water (H2O), and the thin lunar atmosphere p (-OH), can also the related hydroxyl grou he form of bonds exist in lunar minerals in t roxides (rather than in such as hydrates and hyd gly suggest that such free form), and clues stron centration on a large is well the case in low con fact, the adsorbed water art of the lunar surface. In p rations ranging on the surface at concent should exist ally. million, or even more loc from 10 to 1000 parts per

gear equipped with scientific instruments and a 140-kilo- The Chinese lunar program gram lunar rover named Yutu, able to move over an area The People's Republic of China has great ambitions in space, of 3 km2 around its landing point and study the terrain especially in the . Thus, on October during a 3-month mission. 24, 2007, the Chang'e 1 orbital spacecraft is launched by a The Chang'e 4 spacecraft was originally built as a liner in Long March 3A rocket. Its objective was to map and model case of failure of Chang'e 3. Given the success of this mis- in three dimensions certain regions of the Moon. In total, sion, Chang'e 4 was instructed to land on the far side of the 1.37 TB of data was transferred to Earth during this mission. Moon and explore its surface. A telecommunications satel- A orbital probe, Chang'e 2, was launched on 1 lite, dubbed Queqiao was placed a few earlier at October 2010 using a Long March 3C rocket. It came into the L2 Lagrange point of the Earth-Moon system to act as a orbit October 6, 2010. One of the possibilities was that the relay, the Moon obstructing direct communications bet- probe on the Moon at the end of its mission, but it ween Chang'e 4 and the Earth. Chang'e 4 was launched on was put into an orbit of meeting with the near-Earth aste- December 7, 2018 by a Long March 3B rocket and landed roid Toutatis she met December 13, 2012. on the Moon on January 3, 2019 to conduct an exploration On December 1, 2013, China launched Chang'e 3 on a with its rover. This is the first landing of a spacecraft on this Long March 3B rocket. Unlike the two previous probes, side of the Moon. Shortly after the module landed, the Yutu Chang'e 3 carries a rover to land. This is the first craft to 2 rover began rolling on the moon. On February 13, 2019, as land on the moon (December 14, 2013) since the landing the rover began his second lunar night, he traveled 120 m. of the Soviet Luna 24 probe, which brought a soil sample In May 2019, as the rover began his fifth lunar night, he tra- back to Earth in 1976. Chang'e 3 was carrying a landing veled 190 m. In July 1969, together with family or friends around a radio or a rare TV, 600 million people, on all continents, followed the first step of a man on the moon. 50 years later, we have the urge to experience this enthusiasm for the Moon in a global, universal movement that trans - cends all borders. How? Nothing's easier. We want everyone, big or small, to discover at a world event the Moon through a telescope or an astronomical telescope. Surprise passers by offering them this unexpected sight. You have an instrument of observation, install it at the corner of a street, at the edge of a river, on the place of a village ... Join the event On the Moon Again on July 12 and 13, 2019 and invite passersby to observe the moon and share the wonder. www.onthemoonagain.org I F R E H C

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with the support of Société Astronomique de France

Septembre 2011 – l’ ASTRONOMIE - 10