What is Moon: Definition and 1000 Discussions

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. DeliriousEncore

    If the moon's Perigee was closer, could that result in earthquakes?

    If for any reason, the moon were forced into a more extreme elliptical orbit to earth where its perigee was much closer to earth and its apogee was much farther, what kind of affects would we expect to see? Also, would the moon's perigee cause more frequent or more severe earthquakes?
  2. DeliriousEncore

    Extinction event in my story, is it believable?

    I am writing a saga of multiple stories set at different time periods in a fictional version of our real world. At a certain point in the worlds timeline, in the next thousand or so years of the current real world time, an extinction level event wipes out all civilization and most life on earth...
  3. J

    B Could you use the moon to reflect sunlight onto a solar sail?

    I dont know much and you can dumb it down as much as you like or not. I've recently gotten very curious about light propulsion and i was reading that if a laser or beam of light was directed at a solar sail it could generate mass amounts of energy and be used to travel to deep(er) space. I was...
  4. D

    I Is There an Atomic Clock Experiment on the Moon Testing Relativity?

    I learned recently that there are plans to create a dedicated global satellite navigation system (GNSS) for the Moon, so we will have atomic clocks on and around the Moon, but we have at least one there now, in order to compare it with a clock on Earth? You know about such an experiment and its...
  5. D

    Will there be a million people on the moon by 2060?

    What do you think????
  6. Parziter

    Solar System Forces -- Simulating the planetary orbits for my project

    TL;DR Summary: Solar sytem forces on Unity Hello ! For my last year in my school, I've got a project to do, and I wanted to recreate the Solar system with forces on Unity. My forces are Velocity and Acceleration (I'm using the Frenet's formulas). I'm sorry I'm not a physicist and that's why...
  7. Astronuc

    Exploring the Cosmic Connection: Pink Floyd's Dark Side of the Moon at 50

    I remember when the album appeared. It was different. https://www.theringer.com/music/2023/3/1/23617038/pink-floyd-dark-side-of-the-moon-legacy-anniversary-50th There was a lot of great music that year: Aerosmith, Aerosmith, January 5, 1973 Blue Öyster Cult, Tyranny and Mutation, February...
  8. E

    I Research paper and sources investigating Earth's moons

    Hi. I am looking for scientific papers, articles and/or even simulations that investigate how many moons it would be possible for earth to have and maybe modern theories about what these moons can be and look like (i.e what characteristics they have) if they were to exist. I have googled and...
  9. lionpauu

    A Do moon phases affect weighing precision on the microgram range?

    Hi, I'm looking to improve the precision of a system over a several hour cycle of operation of +50°C operation. The mass is ~11g and is suspended below the balance via a factory provided point. The "sample" is enclosed within a large borosilicate flask 150mm dia x 450 mm height that is trace...
  10. DANIELWR1998

    How do I find way of comparing the density of the Earth and the Moon?

    Surface acceleration is proportional to density and radius of planet (as 2 powers of R cancel with the volume) g(moon)/g(earth) = density(moon)*radius(moon)/density (earth)*radius(earth) = (1/4)*density(moon)/density(earth)
  11. LadiSilverfox

    Questions about a habitable second moon

    Good afternoon, I am working on writing a story that is set on a habitable second Moon. I suppose I could easily say it's a mild planet that splits into three main seasons and make up some story about how the first Moon appears every so often for a month of phases and then vanishes. As a...
  12. Klarkaaaa15

    B How does the lunar cycle affect the equinox in the Muslim Hijri calendar?

    Hello, I found this question on the Internet and I would like to ask for help, if anyone knows the answer to it? At what time of day at the autumnal equinox can we observe the third quarter moon on the western horizon?
  13. D

    Will China be the first country to return to the moon?

    I think so. What do you think?
  14. collinsmark

    Stargazing Join the occult (Dec. 7th/8th, Moon will occult Mars.)

    The Moon will occult Mars in less than a week for a good chunk of the northern hemisphere. That's the evening of Wednesday, Dec. 7th, for all of Canada and much of the United States. That's the wee morning hours of Thursday, Dec. 8th, for much of Europe...
  15. F

    A Orbital Radius of a Jovian Moon

    How did the first scientists figure out the orbital radius of a moon of Jupiter? How can observations lead to a calculation of the orbital radius of a moon of another planet?
  16. Paul Colby

    Reusable boosters in moon missions

    I’m with everyone else cheering the Artemis launch and the whole return to the moon bit, but I can’t quite see why reusable booster technology wasn’t used. I realize trade studies are just that, studies. So an answer might be complex. The standard answer is reusable boosters can’t lift as much...
  17. J

    B Why does the moon appear tilted?

    Researching this I found that the usual explanation was that it was an 'illusion'. However this explanation, in my opinion, does not stand-up to the laws governing the transmission of light. I proposed that as light travels in a straight line this poses a problem for moon tilt. Most of the...
  18. mfb

    NASA Artemis 1 going to the Moon (launched Nov 16)

    The Flight Readiness Review (FRR) for Artemis 1 concluded - the rocket is on track for a launch August 29, 12:33 UTC (08:33 local time) or in the two hours afterwards. Backup launch windows are daily from September 2 to September 6. The first flight of the Space Launch System will launch an...
  19. O

    I Is the eccentricity of the lunar orbit constant?

    The wikipedia article on Lunar distance contains a confusing graph. The graph seems to suggest that the eccentricity of the lunar orbit is maximal in january and ~july, and minimal in april and ~october. I think the eccentricity should be constant. Is wikipedia right or wrong, or is there some...
  20. J

    I Gravity on the Moon vs. on the spinning Earth

    "If the Earth were not spinning, you would be heavier as you would feel the full force of gravity."so how does this apply to the moon? the moon does not rotate and therefore you would experience the full force of gravity as stated above,yes,,yet the appolo missions film footage showed...
  21. dirb

    Calculating Angle & Speed to Reach Planet's Moon from Station Orbit

    A station is orbiting a planet at a distance R1, a moon is orbiting the planet at distance R2 with the period T. The planet itself has a radius rp and a mass mp. We know that when an object adds its velocity at a point in the orbit, the height of the opposite orbit will increase. Determine the...
  22. jellybean-spider

    Fields (Gravitational fields) -- Escape Velocity from the Moon

    It's an MCQ, and I chose 4/81 v(esc). Is this correct? There isn't a marking scheme... :cry:
  23. dlgoff

    B Chasing the Moon: Astronauts & Technology".

    I've seen Chasing the Moon several times but it's on a PBS TV channel now and I'm watching it again. It's just amazing how brave those astronauts were and the technology that got them there.
  24. Astronuc

    Rocket possible collision with Moon

    https://arstechnica.com/science/2022/01/an-old-falcon-9-rocket-may-strike-the-moon-within-weeks/ https://www.projectpluto.com/temp/dscovr.htm
  25. dom_quixote

    B The Colors of The Moon (Doppler Effect)

    Hey guys! I will pass an illustrated problem, below. - We know that the solar rays that reach the Moon and Earth are practically parallel; - We know that the lunar orbit with respect to Earth lasts 27.322 days or 2,360,621 seconds; - We know that the lunar orbit with respect to the Earth is...
  26. dedocta

    I Would Icarus' wings fly in Earth's atmosphere and moon gravity?

    Could they generate enough lift for 1/11th the weight of a human? Was picturing a giant warehouse and curious if it would work!
  27. bland

    I Why does Webb orbit L2, is it because of the Moon?

    I was already puzzled by the concept of orbiting a Lagrange point and then I find out it's about the same size orbit as the Moon. I am thinking that if there was no Moon that the Earth and the Sun are far enough away to be treated as points and so that there would be an exact distance further...
  28. A

    Torque imposed by the Moon and Sun on the Earth given its precession

    From the givens: Approximate Earth as a sphere: ##I_e = \frac{2}{5}MR^2 = \frac{2}{5}(5.97x10^{24})(6.371x10^6)^2 = 9.69x10^{37} kg*m^2## ##\omega_e = 7.29x10^{-5} \frac{rad}{s}## To calculate the rate of precession of the disk the Earth precesses around (1 revolution every 26,000 years)...
  29. J

    Cesium-133, the Sun, Moon, stars, or.... T.P. Scott-1000?

    Early in the pandemic there was, at least in the U.S., a concern about toilet paper shortages. It all seems so quaint now but there were actually runs on t.p. in supermarkets and people were hoarding it. There are of course other ways to clean up afterwards. I reckon that most people in the...
  30. Lren Zvsm

    Sapient Life Indigenous to a Planet Orbiting a Red Dwarf

    I am considering writing a story that features aliens indigenous to a planet orbiting a red dwarf star. Even so, because of its proximity to the red dwarf, the planet's surface receives much more radiation than Earth's surface does. What is more, the planet has no moon to stabilize its...
  31. I

    Calculating the Force of a Jump on the Moon

    From my understanding, at an elementary physics level, the height at which we can jump depends on acceleration due to gravity and the initial velocity when we leave the ground. We can calculate our initial velocity by calculating acceleration and using the distance we bend down before jumping to...
  32. sigurdfromnor

    (Movement Homework) What is the speed of a marble falling on the moon?

    Sorry for the bad english. This might sound stupid but I am pretty new the physics and i can't seem to find what formula to use on this problem when only the mass, gravity and height of the fall is given. and i can't find a similar problem in the book, could someone give me any pointers? Thanks...
  33. Astronuc

    Chasing the Moon, PBS documentary

    We're now familiar with the Hidden Figures within NASA's space exploration programs. Another program explores further contributions (2019). https://www.pbs.org/wgbh/americanexperience/films/chasing-moon/?feature_filter=All The Women Who Brought Us the Moon...
  34. A

    B Why can we only see one side of the moon?

    I have learned that the moon has rotation as well the Earth, so why we can see only one side of the moon? With the moon's rotation, at some point, we must see all sides. Can anyone explaine why it does not happens?
  35. Limebat

    B Can you use hand tools on the moon?

    No, this isn't a homework question. I'm genuinely curious; If I were to magically teleport and happenstance with a shovel and survive the harsh climate, could I use said shovel? Maybe hand drills? I would assume the shovel would be a class one lever, and thus the moon's lower gravity would...
  36. xpell

    I If Jupiter had a 5th large moon until "recently", would we know?

    Hi! I'm fascinated by the apparent "concentration" of the four large Galilean moons in a barely 1.5 million km "strip", and the vast, "empty" distance to the next moons (moonlets?) Out of a purely aesthetic sense of horror vacui, :wink: I've always wondered if there was at least another Jovian...
  37. T

    B Seeing a half Moon - where is the Sun?

    A little off subject, but a few years ago I went out fishing just as the sun was rising. Perfect morning, not a cloud in the sky. The moon at this stage, was still clearly visible and both the moon and the entire sun were sharing the same sky. Which is pretty cool but what to this day makes me...
  38. M

    B Can a Planet Have a Moon that Never Casts a Shadow?

    I am a newbie, and really uninformed (read stupid.) Here is my question: Would it be possible for the Earth (or any planet,) to have a moon whose orbit was such that it never came between the sun and the Earth? In other words, could we have a moon that never cast a shadow on the Earth? Or is...
  39. mfb

    #dearMoon: Flight around the Moon accepts applications

    dearMoon website Japanese billionaire to fly eight members of the public on SpaceX moon flight The number of spaceflight seats open to the general public (not only multimillionaires and career astronauts) just increased from 2 to 10. And it's not just orbiting Earth - it's going to the Moon...
  40. jim mcnamara

    Full moon names: somewhat bogus but fun.

    Happy Snow Moon - whatever that is. Why? Have you noticed the plethora of "moon names" we are bombarded with - usually applied to the full moon? As an example these names are asserted to be "Native American" names for 12 months https://www.almanac.com/full-moon-names Re: the list above --...
  41. A

    Would He3 make fusion easier? :- Can a fusion rocket launch from Moon?

    Heard talk about He3 on the Moon and launching a fusion rocket. Is this all just a mashup of Sci-fi ideas?
  42. K

    Questions on operating a nuclear power plant on the Moon or Mars

    Heat cannot be removed by liquid-to-gas heat exchangers since there is no substantial atmospheres on the Moon or on Mars. It cannot be dissipated by venting steam since there is a critical water shortage. It cannot be dissipated by rocks or soil since both are essentially thermal insulators. It...
  43. artriant

    B Earth & Moon Gravity Gradient: Investigating Its Impact

    Hello everyone, happy holidays! Y/day i googled that question (see title), and i found no clear answer, and I was really suprised, So I had to investigate my self, this is a super basic question, Let me know if i got this right: Earth R: 6,371 km Moon R: 1,737.1 km d1: 384,400 km (center to...
  44. Incnis Mrsi

    I Infrared energy flux from the Moon

    I am interested in energy flux density from the Moon at Earth’s surface, specifically in infrared (albeit most of it comes in infrared anyway). Physics.SX (boyfarrell) gives an estimate 89 mW/m². I doubt it for several reasons. 400 K (as effective mean) on Moon seems to be unrealistically hot...
  45. sophiecentaur

    Viewing Distant Celestial Objects: Could Hubble Have Seen the Moon Landings?

    Mentors' note: This thread has been split off from https://www.physicsforums.com/threads/viewing-distant-celestial-objects.997168/ If it were possible for Hubble to have seen evidence of Moon landings, those batty conspiracies about the landings being fake would have died long ago.
  46. lola1227

    Forces Experienced On Moon and Earth - What is the mass?

    So, I decided to do Fg=ma I tried 25(9.8)=1.62m m= mass However, when i did it i got a mass of 151 but when i put it into its separate equations, the fg is not 25x larger so fg=ma fg=151(9.8) = 1479.8and then fg=ma fg=151(1.62)= 244.62 but 1479.8/244.62 is not 25 it ends up being 6.05...
  47. Greg Bernhardt

    NASA discovers water on the moon

  48. I

    Period of a Pendulum on the Moon

    The equation that governs the period of a pendulum’s swinging. T=2π√L/g Where T is the period, L is the length of the pendulum and g is a constant, equal to 9.8 m/s2. The symbol g is a measure of the strength of Earth’s gravity, and has a different value on other planets and moons. On our...