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. DennisN

    Stargazing The Moon through my El Crapo Telescope

    Hi, I just managed to take my best picture up to this time of the Moon through my crappy $35 scope. Professionals would have cried if they looked at my setup :biggrin:: a Chinese $35 telescope a really (REALLY) unstable mount a mobile phone camera held up by hand in front of the eyepiece, set...
  2. DaTario

    I Why is the Moon getting further from Earth ?

    Hi All, What is the reason that makes the distance between the Earth and the Moon get larger and larger? Best wishes, DaTario
  3. BillTre

    Did you know today is National Moon Day?

    https://nationaldaycalendar.com/2018/07/19/july-20-2018-national-moon-day-national-lollipop-day-national-pennsylvania-day/ Enjoy! Its also National Lollipop Day and National Pennsylvania Day. So, triple enjoy!
  4. S

    I Does the barycenter of the Earth-Moon system change?

    Hi to all! My question is: Does the relative position of the barycenter of the Earth-Moon system change due to mass distribution changes in the system and would this affect the Earth-Moon distance? For example: Could the sea level rise change the Earth-Moon distance? The only formula I found...
  5. J

    Projectile Motion on the Moon: Finding the Optimal Launch Angle Using Equations

    Homework Statement A cannon can shoot whatever cannons shoot at different angles to the horizon, but with the same initial velocity. At what angle does the cannon shoot to a maximal distance? What would be that angle on the moon? Homework Equations d is the total horizontal distance traveled...
  6. S

    The question: Can nitrogen molecules escape from Europa and into space?

    Homework Statement :[/B] An astronaut visiting Jupiter’s satellite Europa leaves a canister of 1.20 mol of nitrogen gas 28.0 g/mol^2 at 25.0°C on the satellite’s surface. Europa has no significant atmosphere, and the acceleration due to gravity at its surface is 1.30 m/s2. The canister springs a...
  7. isukatphysics69

    GPE Between the Moon and the Earth?

    Homework Statement How to determine GPE between moon and earth? Homework Equations mgh The Attempt at a Solution I know that gpe near Earth's surface is mgh, but at larger distances is there a specific way to calculate?
  8. isukatphysics69

    Gravitation between the Moon and the Earth: physics project

    Homework Statement Homework Equations f = ma m1 = mass of moon m2 = mass of earth The Attempt at a Solution Ok this is crunch time here and i am NOT Kobe Bryant I have chosen gravitation between the moon and Earth for this project. I will start with the net force on the moon as ∑FSystem =...
  9. A

    I Origin of the Moon: Latest Discoveries and Theories

    What's the latest about the origin of the moon? Is it true the moon is older than the earth? how?
  10. Physics345

    B Why does the flag on the moon appear to be waving during the Apollo 13 mission?

    Hi Everyone, Can someone please explain to me why the flag is moving as if wind is blowing on it during the Apollo 13 mission? I am well aware that it's not actually wind blowing on the the flag causing it to move, but I still would love to know why this occurs. Note: I am very uneducated...
  11. DLeuPel

    I How can General Relativity explain the Moon drifting apart from Earth

    According to various sources, the Moon is separating from Earth 4 cm every year. I’ve searched for the explanation and I’ve found the following: The friction the seas and oceans from the Earth make with it’s soil causes the Earth’s rotation to slow down. This causes the Moon to speed up...
  12. PlanetGazer8350

    Calculate iron container acceleration in railgun system on the Moon

    Having a cylindrical iron container with wall thickness of 20 cm, and a total weight of 500 tons when filled with its cargo, how would you be able to calculate its required voltage and current input in a vertical railgun system (relative to the Moon's surface), with an exit acceleration of...
  13. J

    Is it possible to pour concrete in a vacuum?

    One idea for a moon base would be reinforced concrete domes, but is pouring concrete in a total vacuum even possible? Wouldn't the water just evaporate, or is there another material we could use instead of water? Are the ingredients of concrete plentiful on the moon, or could we synthesize them...
  14. A

    I Changing the ISS's orbital inclination to match the Moon

    What is the practical feasibility of changing the International Space Station's orbital inclination to match the orbit of the Moon? Major future missions beyond the Earth-Moon system (ie: space colonization) will likely require in-orbit assembly of components from multiple launches. And...
  15. Alexanddros81

    Calculate the maximum and minimum distances between the Earth and the Moon

    Homework Statement 14.100 Calculate the maximum and minimum distances in kilometres between the centers of the Earth and moon, taking the eccentricity of the moon's orbit into account. Use the data given in Prob. 14.99 Homework EquationsThe Attempt at a Solution Can you check my solution...
  16. Alexanddros81

    Compute the distance between the Earth and the Moon

    Homework Statement 14.99 Assuming that the orbit of the moon around the Earth is a circle (its eccentricity is actually 0.055), and knowing that the period of the orbit is 27.3 days, compute the distance in kilometres between the centers of the Earth and moon. Homework EquationsThe Attempt at...
  17. J

    B The Moon's inclination to Earth's equator

    Is there an on-line calculator or a table that would allow me to plug in a date (year) which would give me the moon's inclination to the plane of the equator on that date? Thanks for any help.
  18. zdcyclops

    B If the moon were a light bulb how many watts would it be.

    If the moon were a light bulb how many watts would it be.
  19. lekh2003

    Super Blue Blood Moon: Did Anyone See It?

    I just wanted to see anybody's opinion on the super blue blood moon yesterday night (at least for me). I couldn't catch a glimpse of it in Sydney since it had been very hot for a few days and clouds had taken over the sky. I could however see an unusually bright red tint in one area of the...
  20. Charles Link

    B Tonight's full moon and lunar eclipse

    Hello, I don't see any other post about tonight's full moon and lunar eclipse, so I thought I would mention it.
  21. John Mohr

    Would a Very Large Mass (e.g. the Moon) Fall with g?

    Today, I had a thought experiment where I began to puzzle over inertia of very large masses being dropped. Imagine a scenario where the Moon was suspended 100 m from the surface of the Earth alongside a marble at the same height. Now ignoring air resistance and the gravity exerted by the Moon...
  22. riveay

    Simulating Jules Verne Earth to the Moon trip?

    Has anybody attempted simulating the trip to the moon described by Jules Verne? I've done a bit of research and found this two posts: https://www.physicsforums.com/threads/showing-deadly-acceleration.909104/#post-5726115...
  23. A

    I Optimizing Lunar Power: North vs. South Poles for Mining and Moonbase Sites

    North or South? Which is better for prospecting, mining, a site for a Moonbase and solar power. This could be quite a crucial question. The first solar array in permanent (ish) sunlight will stake a claim, because the next one will threaten to put it into shadow at certain times in the Lunar day.
  24. wolram

    B New Topographic Map of Saturn's Moon Titan Reveals Liquid Flows

    Using the now-complete Cassini data set, astronomers have created a new global topographic map of Saturn's moon Titan that has opened new windows into understanding its liquid flows and terrain. https://www.sciencedaily.com/releases/2018/01/180106190439.htm I found this fascinating I hope others do.
  25. Rednecknav

    I Moon vs Earth for launch to Mars

    Problem - we have to use large amounts of fuel/propellant to exit the Earth's atmosphere to enter Earth orbit, the moon or other planets... Solution - would it not make sense to launch from a base on the moon? Problems I see, potentially... 1) Is the moon’s orbit around Earth problematic for...
  26. mr1batman

    B Distance between the Earth and The Moon

    we know that the moon is far away the distance between us and the moon can fit all the other 7 planets and some small dwarf planets but how ? it would take us 3 days to reach the moon and the spacecraft were traveling in at least 240,000 miles it should take us more than a year to reach the...
  27. P

    Maintaining interest in the new 'private' space race

    It's said that expectations drive the economy. So, how do you maintain interest in something that has no immediate bearing/benefit/utility of a population? I would think the answer to that question is to manifest a 'goal', in this case being an interplanetary species or even just building a...
  28. ISamson

    What is the latest book about a Moon base by author Andy Weir?

    Hello. I wanted to discuss an interesting recent article on space.com which talks about a book released on the 14 November talking in incredible detail about a Moon base. The article features an interview with the author describing the book and his intents. Cool.
  29. mark!

    I Resemblances between moon surface and earth mantle

    The Theia hypothesis is the current leading hypothesis to explain how our moon was created. Both Earth's mantle and the moon's surface have indistinguishable oxygen isotope ratios, which leaves the earth–moon system as more similar in O isotopes than any other two bodies in the solar system...
  30. davenn

    NASA New moon map from NASA .... VERY zoomable

    this will blow your mind ! https://sservi.nasa.gov/articles/lroc-quickmap-try-it-out/ click on the blue colour "Quickmap" link in the first paragraphDave
  31. B

    Does the moon orbit as a classical particle?

    The moon orbits Earth at a radius of 3.84E8 m. To do so as a classical particle, its wavelength should be small. But small relative to what? Being a rough measure of the region where it is confined, the orbit radius is certainly a relevant dimension against which to compare the wavelength...
  32. C

    The Factors affecting the Orbitals of a moon

    1. Pull of gravity on moon/mass. 2. Velocity of Moon 3.Mass of moon 4.Infuence of other nearby mass's gravity I believe there are many more factors that influences an orbital. Am I right?
  33. sophiecentaur

    Stargazing Focussing a Pentax K S2 with Live View for Moon Photography

    I have been struggling with focussing my Pentax K S2 using Live view. The image of the Moon (or the Sun, with filter) is too burned out to focus. The photos are OK so the camera takes care of that. Anyway, I have a tedious workaround which involves focussing on a bright star (with bhatinov...
  34. C

    Stargazing Looking for a beginner's telescope....

    Hi there, I love physics and I'd like to begin a bit of astronomy. I want to invest in a beginners telescope but I haven't a clue about what to buy. Some that I'm looking at are linked here: https://www.amazon.com/dp/B00XQMLA7Q/?tag=pfamazon01-20...
  35. T

    B Is there a way to prove that men have gone to the moon

    It's frustrating to see plenty of videos on YouTube and websites across the internet claiming that men has never walked on the moon or that the Apollo mission was a fraud. I do believe that the land on the moon happened. On the other hand, it's on the heart of science to consider all claims...
  36. C

    B Uranus's Moon Cressida is Doomed

    The first measurement of the mass of a small Uranian moon suggests it will be obliterated by smashing into another moon in a mere million years. By Ken Croswell Full story: New Scientist
  37. E

    Why does the Moon sometimes seem red?

    Hello all, as i write in the title my question is about the colour of the moon. Yesterday evening, i saw the moon rising to the sky in a red colour. Why is this happening? Is it an atmosphere/ gas problem?
  38. A

    B Accuracy of moon orbiting earth in how many days and hours

    Can anyone tell me accurately. accuracy of moon orbiting Earth in how many days and hours and seconds and if it is multiplied by 14 how much it will be in days. i need accurate answer. Thanks, Ahmed.
  39. S

    I Mysterious Agent Blows Up Moon: Can Earth Survive?

    Story in brief: An unknown agent blows up the moon, initially into 7 major pieces and a bunch of little ones. The pieces are gravitational bound, but collisions between the pieces continues the break up process. Stephanson postulates that the number of pieces reaching the Earth's atmosphere...
  40. Ron Burgundypants

    Momentum of a moon after a meteoroid strike

    Homework Statement Phobos is a small moon of Mars. For the purpose of the following problem, assume that Phobos has a mass of 5.8x10^15 kg and that it has a shape of a uniform sphere of radius 7.5x10^3 m. Suppose that a meteoroid strikes Phobos 5.0x10^3 m off center and remains stuck. If the...
  41. V

    I Comparison of tidal forces acting on the Moon vs Enceladus

    I have heard about a moon Enceladus. Which is powered by tidal force. I suppose this force press back and forth on the moon and friction in the core causes heat. I hope I'm right :-) Now tidal force ##F_t=\frac{2GMmr}{R^3}##, where ##G## is Gravitation constant, ##M## is mass of planet causes...
  42. Deepak K Kapur

    B Effect of the Sun's Gravity on the Moon

    Is the gravitational pull of Sun on moon greater than the gravitational pull that Earth has over moon? Thanks.
  43. Chatterton

    Living on the far side of a tide-locked moon

    You're the Galileo for a developing society on a remote archipelago on the far side of a tide-locked moon orbiting a gas giant. How do you figure out your place in that solar system? How do you convince others, who believe your world to be the center of the universe, of the truth? Will a road...
  44. I

    I Are there hidden phenomena under the moon that only the naked eye can see?

    When I look up at the moon at night, I see something peculiar. It looks as if the moon is rolling on something for which I will not say. When I put my thumb to it, I can really get the image to open up. The phenomena is not apparent at all when viewed with aide of telescoping lens. Only bare...
  45. J

    Pulse echo technique to find the distance of the Moon

    Homework Statement [/B] Over 40 years ago, the Apollo astronauts placed reflectors on the surface of the Moon. These are still used by a number of observatories on Earth to monitor the distance to the Moon by reflecting pulses of laser light from them and detecting the reflected signal...
  46. ImMaybeBrian

    B Potential Impacts of Helium-3 Mining on the Moon and Human Health

    There's been talk about extracting Helium-3 from the Moon as a source of nuclear fusion energy because of it's efficiency and nonradioactive-ness--but I haven't seen anyone talk about any kind of side effects it could have either on the Moon itself, to people, etc. I understand because of it's...
  47. C

    Laser Physics - Diameter of a Spot on the Moon from a Laser

    Was not sure whether to post here on in the advanced section, since it is part of a final year undergraduate module, yet seems like a pretty simple problem (though I still need help! haha). 1. Homework Statement A frequency doubled Nd:YAG laser (##\lambda = 532##nm) with an initial beam...
  48. Z

    NASA NASA's Mars Plan May Include a Yearlong Mission to the Moon

    A group of astronauts may spend a year in orbit around the moon in the late 2020s as part of NASA's plan to send humans to Mars in the 2030s, agency officials said today (May 9). Greg Williams, NASA's deputy associate administrator for policy and plans in the agency's Human Exploration and...
  49. EthanVandals

    Calculate Moon's Potential/Kinetic Energy, Escape Velocity & Period

    Homework Statement Calculate the potential energy and kinetic energy of the moon, as well as it's escape velocity. Give the moon's period and angular speed. Consider the Earth to have a mass of 6 x 10^24 kg, the moon to have a mass of 7 x 10^22 kg, and their center separation distance to be 4 x...
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