Moon Definition and 1000 Threads

The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia), it is the largest natural satellite in the Solar System relative to the size of its planet, the fifth largest satellite in the Solar System overall, and is larger than any dwarf planet. Orbiting Earth at an average distance of 384,400 km (238,900 mi), or about 30 times Earth's diameter, its gravitational influence slightly lengthens Earth's day and is the main driver of Earth's tides. The Moon is classified as a planetary-mass object and a differentiated rocky body, and lacks any significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is about one-sixth of Earth's (0.1654 g); Jupiter's moon Io is the only satellite in the Solar System known to have a higher surface gravity and density.
The Moon's orbit around Earth has a sidereal period of 27.3 days. During each synodic period of 29.5 days, the amount of visible surface illuminated by the Sun varies from none up to 100%, resulting in lunar phases that form the basis for the months of a lunar calendar. The Moon is tidally locked to Earth, which means that the length of a full rotation of the Moon on its own axis causes its same side (the near side) to always face Earth, and the somewhat longer lunar day is the same as the synodic period. That said, 59% of the total lunar surface can be seen from Earth through shifts in perspective due to libration.The most widely accepted origin explanation posits that the Moon formed about 4.51 billion years ago, not long after Earth, out of the debris from a giant impact between the planet and a hypothesized Mars-sized body called Theia. It then receded to a wider orbit because of tidal interaction with the Earth. The near side of the Moon is marked by dark volcanic maria ("seas"), which fill the spaces between bright ancient crustal highlands and prominent impact craters. Most of the large impact basins and mare surfaces were in place by the end of the Imbrian period, some three billion years ago. The lunar surface is relatively non-reflective, with a reflectance just slightly brighter than that of worn asphalt. However, because it has a large angular diameter, the full moon is the brightest celestial object in the night sky. The Moon's apparent size is nearly the same as that of the Sun, allowing it to cover the Sun almost completely during a total solar eclipse.
Both the Moon's prominence in the earthly sky and its regular cycle of phases have provided cultural references and influences for human societies throughout history. Such influences can be found in language, calendar systems, art, and mythology.
The first artificial object to reach the Moon was the Soviet Union's Luna 2 uncrewed spacecraft in 1959; this was followed by the first successful soft landing by Luna 9 in 1966. The only human lunar missions to date have been those of the United States' Apollo program, which landed twelve men on the surface between 1969 and 1972. These and later uncrewed missions returned lunar rocks that have been used to develop a detailed geological understanding of the Moon's origins, internal structure, and subsequent history.

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  1. N

    How Does Acceleration Affect an Astronaut's Apparent Weight Near the Moon?

    What is the apparent weight of a 75-kg astronaut 4200 km from the center of the Earth's Moon in a space vehicle (a) moving at constant velocity, and (b) accelerating toward the Moon at 2.9 m/s^2? State the "direction" in each case. I understand part a. I got 21 Newtons towards the moon by...
  2. N

    Do Mirrors in Quantum Experiments Act as Measurement Devices?

    Considering (again!) which way type of experiments (the interference type of set ups when a photon may go through two different routes and then one recombines the paths and checks for the presence of absence of interference (as used in quantum erasers, etc)). Usually, people say that if there...
  3. W

    Venus Escaped Moon GravitySimulator Update

    Back in the old celestial mechanics forum, I wrote about a simulation in GravitySimulator where I created a moon with twice the mass of Mercury, and set it in orbit around Venus, right at Venus's L1 distance. The moon orbits a few times and then gets left behind. I thought at first that Mercury...
  4. H

    Why Going to the Moon is Taking 16 Years This Time Round - Hugo Rune

    I remember seeing old TV footage from 1961 of Kennedy promising to get to the moon before the end of the decade, which they succeeded in doing with Apollo 11 in July 1969. All the planning, designing, building and testing, the successes and failures, redesign, rebuild, retest, the development...
  5. R

    Will Russia Build a Nuclear-Powered Moon Base by 2015?

    [SOLVED] Russkies are going to the moon! The head of Energia, Nikolay Sevastyanov, is planning to build a nuclear-powered moon base by 2015, so that they can extract lunar ^3He and send it back to earth. http://english.pravda.ru/science/19/94/379/16403_moon.html...
  6. P

    Placing an Asteroid in Moon Orbit: Is It Possible?

    So had an idea the other day, and...Too make a gob of statements that started out incoherently seem coherent this is what I was thinking of doing: Take an asteroid (roughly 2 million pounds in weight) from the asteroid belt and place it in moon orbit. Please don't ask me about how I would...
  7. P

    Frequency of Pendulum on Moon: 1.18 Hz

    A pendulum consists of a mass m = 0.070 kg hanging from a flexible string of length L. The string is very thin, very light, and doesn't stretch much. It makes small oscillations, with a period of 0.704 s. Find the oscillation frequency of the pendulum. Neglect any air resistance. I got this...
  8. Q

    Why has the US been the only nation to land on the moon?

    I do believe atsronauts landed on the moon, I was recently reading space.com and it said "for people who don't know much physics, the idea that landing on the moon (not doing it) may seem possible" so I came to this forum to ask the question. I've looked at all the theories saying we...
  9. Pengwuino

    Proof the moon landings were fake

    http://www.brainsluice.com/miscellanea/misc/moonlanding.html As you can see... there is plenty of evidence contrary to the NASA lie of us landing on the moon. http://www.brainsluice.com/miscellanea/misc/images/moonlanding06.jpg Notice the crosshairs inserted by the NASA editing crew...
  10. M

    Examining the Evidence: Were the Moon Landings Real or Fake?

    Hi, I am a grade 11 student currently taking physics 20. For an assignment, I was asked to prove whether or not I thought the moon landings really happened, or if they were faked. If anyone can hit me up with evidence for either case, that would be cool. :smile: :smile: :smile: :smile: :smile:
  11. A

    Calculating the Angular Momentum of a Moon Orbiting an Earth-like Planet

    There is a moon orbiting an Earth-like planet. The mass of the moon is 4.77e22 kg, the center-to-center separation of the planet and the moon is 616000 km, the orbital period of the moon is 25.6 days, and the radius of the moon is 1590 km. What is the angular momentum of the moon about the...
  12. S

    Settlement on Moon: Artificial Gravity & Feasibility

    If a settlement is ever setup on Moon, would it require artificial gravity. Would it be feasible to rotate such a large settlement using bearings and rockets?
  13. W

    Mysterious Spin of the Moon: How Does it Change?

    i have been thinking about how the moon always faces Earth from the same side. this means that the moon spins once per rotaion but how perfect is this does the side of the moon that we see slowley change over time or in 2000 years will we be looking at the other side. the spin of the Earth is...
  14. S

    Finding Equal Force Distance from Moon

    So I am supposed to find the distance from the moon where the force on a particle from the Earth and sun is equal. I get this expression (earth-moon distance is 400 000km): yMm/(r^2) = yMm / (400000km-r)^2 But from that I get r=200 000km and the answer should be 40 000km... whats wrong...
  15. A

    Heard the moon is moving away from us

    i heard the moon is moving away from us, does that mean its orbital speed has increased? how will that affect the rotational speed of Earth on its axis? slower?
  16. Z

    Stargazing How can stacking improve astrophotography?

    Just finished this... I thought i`d attempt a mosaic and the moon looked rather seductive a couple of weeks ago low in the westen sky so i htought i`d take a few picks.
  17. O

    What is the Minimum Velocity Needed for the Moon to Avoid Crashing into Earth?

    I'm not sure if this has been asked before, I searched the forum but didn't find anything. Anyway, I was wondering what minimum velocity the moon can have without crashing into the Earth due to gravity (basically the opposite of the escape velocity).
  18. L

    Was America's moon expedition a fake?

    Even people ignorant of space technologies understand that then-level of technological and electronic development wouldn't allow to perform complicated space maneuvers. Forty years ago, American President John Kennedy urged the people to get united about the Moon landing idea: the USA wanted...
  19. B

    NASA Roswell and Nasa Moon Expedition

    not sure exactly where to put this so general discussion sounds good. Last night i was once again watchin TV flipping throguh channels so i stopped on discovery about half way through this issue. I don't remeber who this guy was i believe he used to be sumthing to do with US government and...
  20. A

    Between the moon and the Earth a Spaceship travels

    between the moon and the Earth a Spaceship travels. A person goes on a spacewalk and pushes the tractor trailer sized vehicle. Will the person be pushed back even though things in zero gravity have no mass?
  21. A

    Astronauts Jump So High on Moon: Weight and Atmosphere Matter

    Astronauts on the Moon can jump so high because 1) they weigh less there than they do on Earth. 2) their mass is less there than it is on Earth 3) there is no atmosphere on the Moon I believe the correct answer is 1, because they weigh less. Choice 2 has got to be wrong since mass...
  22. B

    How Long Does It Take for a Feather to Fall 1 Meter on the Moon?

    On the Moon the acceleration... On the Moon the acceleration of freefall is 1.7 m s-2. How much time would it take for a featherto fall a distance of 1.0m from rest? Im not bothered about the answer i just need to know what formula(s) to use and how. These are the formulas i was given...
  23. A

    Why doesn't the moon fall on earth?

    I am curious as to why the moon doesn't fall into the earth. Did a few searches and found: https://www.physicsforums.com/archive/t-58667_Why_doesnt_the_moon_just_fall_to_the_earth?.html But that doesn't explain one thing. Moons orbit is not an exact circle. Its "almost" circular. So...
  24. vincentm

    What would be the effects of Earth not having a moon?

    What would be the effects of Earth not having a moon? I know that our moon is slowly drifting away. But what would happen then?
  25. R

    Is the Moon there when nobody looks at it?

    Please help me with this. Can anyone direct me to the specific mathematics that is interpreted as saying that "the Moon does not exist when nobody looks at it." Is there any book or discussion of the actual math and physics of this? What specifically was Einstein reacting to when he said: "I...
  26. ohwilleke

    How closely could the Moon orbit the Earth

    without having devistating consequences for Earth? My kids (6 and 4) came up with the question last night at bedtime and it is an interesting one. Clearly, none of the moon can contact the roughly 65 miles above Earth that includes the atmosphere, and given its size that puts a bare...
  27. A

    How Many People Went to the Moon?

    there are one man with 7 wives each wive has 7 daughter each daughter has 7 maids each maids has 7 kids each kid has 7 cat each cat has 7 cotton ball each cotton bal has 7 color All of them go to the moon how many man go to the moon ?
  28. K

    Discover the Moon's Beauty - Google Moon

    Zoom into see what the moon's really like: http://moon.google.com/
  29. P

    Seeing Mars as a Full Moon: A Hoax?

    someone told me that in the near future we'd be able to see Mars as the size of a full moon from earth. later i read it was just a hoax. anyone else heard about this?
  30. P

    Is the moon made of green cheese?

    A recent spate of now closed threads gave me an irriisistable impulse to ask this question...
  31. B

    Does anyone know where in the world i can see such large moons?

    Couple of months ago there was a thread on Orange moons (but not bears), with http://home.hiwaay.net/~krcool/Astro/moon/moonorange/ website showing a ..giant moon. Does anyone know where in the world i can see such large moons?
  32. C

    Side of tide due to moon and sun's gravitational pull

    Hi everyone, sorry if I'm new to this and this subject have already been posted, but i have a test tomorrow, and i need help. The question is that when the sun, the moon, and the Earth are in a straight line, with the moon is in between the sun and the earth. It is reasonable to think that the...
  33. F

    Can We Overcome Challenges to Colonize the Moon?

    I don't really know where this should go its more about the people ON Earth then it is about Earth itself so I suppose it can go in this thread Anyways my question is: Do you think we'll be able to colonize places like the moon? What do you think would be the problems with doing that...
  34. B

    If the tides on earth one meter high how far away is the moon?

    Hi all, I am reviewing for my final and cannot seem to find how to solve the following If the tides on Earth one meter high how far away is the moon? What equations should I use to calulate how the moon effects the tides on earth?
  35. U

    Exploring Tunnel Construction on the Moon and its Potential Benefits for Earth

    I was given the equation for the period of oscillation thought a tunnel:T=2 \pi \sqrt{\frac{R_E^3}{GM_E}} then asked how I could transform that into T=2 \pi \sqrt{\frac{R_E}{g}} which I did through the idea that g=\frac{GM_E}{R_E^2} The the question asked what would be the period if...
  36. G

    The Moon's Rotation and Why it Doesn't Spin: Theories and Explanations

    I've seen this mentioned on another post but some questions remain, the Earth rotates about it's axis as I understand it and the moon rotates about the Earth every 28 ish days, the moon has no axis rotation so we only see one side of the moon, is that right? This I can grasp, however why...
  37. D

    Debunking the Moon Landing Hoax Theory

    I personally think it was after reading sites such as these: [ woo-woo links deleted ] Just wondering what everyone's thoughts are on this topic... (I hope I don't get banned :frown: )
  38. U

    Gravitational potential energy of the moon

    How much work is done by the moon's gravitational field as a 1000kg meteor comes from outer space and impacts the moon's surface? all I have to do is: U=-\frac{Gm_1m_2}{r} where _{m_1} is the mass of the moon, _{m_2} is the mass of the meteor, and _{r} is the radius of the moon. is that...
  39. N

    Calculating Tension in the Cable to Hold the Moon

    Q.Suppose the moon were held in its orbit not by gravity but by the tension in a massless cable. You are given that the period of the moon's orbit is T = 27.3 days, the mean distance from the Earth to the moon is R = 3.85 x 108 m, and the mass of the moon is M = 7.35 x 1022 kg...
  40. M

    Moon & Tides: Learn How They're Connected

    Morning everyone! I was up late a few nights ago and I noticed how large the moon looked in the sky. Being a creature of habit myself, I began to wonder why the moon controls the ocean tides. I've been thinking about it and I couldn't come up with an answer. The moon controls the tides. Thats...
  41. M

    Moon Moving Away: Effects & Possibilities

    I hear that the moon is steadily moving away from the earth. Is it due to the suns gravity? Will it eventually go out of Earth orbit and circle the sun on its own? Would there be any chance of a posssible collision with Earth if this happened or would it leave Earth orbit at its closest...
  42. Pengwuino

    What Causes the Moon to Appear Orange?

    So what causes the moon to be orange? I saw one such display about an hour ago going to get food and i was like "aww... big cheese wheel... I am going to eat the moon". So what cuases that?
  43. S

    The Impact of a Moonless Earth: Effects on Tides and Beyond

    No Moon :( What would happen to the Earth if suddenly Moon was gone?Except no more tides I can not think of something else.
  44. T

    Why Can't We See the Other Side of the Moon?

    It's a simple basic question.But I don't know the answer exactly. Why we can't see the other side of moon?
  45. O

    Why is the moon drifting into space

    My astronomy book tried saying that the moon is spinning into outer space, away from earth,; it was blamed on tidal effects between the Earth and moon and the subsequent generation of frictional forces. I don't see it. Also, from physics, if you look at a force diagram there should only be...
  46. E

    Will an Astronaut Float at the Positional Median Between Earth and Moon?

    If an astronaut is located close to the positional median between the Earth and its moon, will the astronaut float around as if it was not being effected by gravity for the same reason that a person in an elevator in free fall would float around being unable to use a measuring device to...
  47. N

    Can a Website Show Historical Moon Phases and Sky Positions for My Location?

    I was wondering if there is a site that shows the moon phases for my specific location up to 20-30 days old. I need to know how much of the moon was showing that day, and idealy the part of sky it was in (high or low to horizon) and the weather conditions for that day (e.g. cloudy, clear, etc.)...
  48. M

    Why The earth and the moon attract each other with a gravitational force

    hey...heres a question that's been bugging me "The Earth and the moon attract each other with a gravitational force. How does the force acting on the more massive Earth compare to the force acting on the moon?" Choices: a.) there is a greater force acting on the earth. b.)the same force is...
  49. W

    Can the Moon's rotation be affected by Earth's tides?

    Our moon does not turn ?? Not at all ?? One would think that after a milenia of being bombarded by comet debris and asteroids that they would have nudged it a little..? couldnt we spin it ourselves .? I for one am tired of looking at the same view of the moon ,every full moon same...
  50. I

    The Moon and the Anthrorpic Principle

    1)If our moon did not exist in the precise configuration it has now would intelligent life have failed to evolve on earth? (There might have been slight differences but I feel the absence of a moon would not have prevented intelligent life evolving on this earth.) 2)The Anthrorpic...
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