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51

The moon does not fall to Earth because it is in an orbit. One of the most difficult things to learn about physics is the concept of force. Just because there is a force on something does not mean it will be moving in the direction of the force. Instead, the force influences the motion to be a bit more in the direction of the force than it was before. ...


32

Briefly: Because the moon's orbit "wobbles" up and down, so it isn't always in the plane of the earth's orbit around the sun. There's a 2D plane you can form from the ellipse of the earth's orbit and the sun. This plane is known as the ecliptic. The moon's orbit is not exactly in the ecliptic at all times; see this (slightly overcomplicated) picture from ...


29

The relevant "100%" from which you should calculate the percentage isn't the depth of the ocean but the radius of the Earth $$ R\sim 6,378,000\,{\rm m} $$ Multiply this $R$ by $10^{-7}$ and you will get $0.6$ meters, a reasonable estimate for average tides. You must understand that the surface of the ocean always tries to create an "equipotential surface" ...


24

It will never reach such a high velocity. The moon is drifting further from the earth due to tidal acceleration. This process is, at the same time, slowing the rotation of the earth. Once the earth's rotational period matches the moon's orbital period, the earth-moon system will be tidally locked to each other (note: the moon is already tidally locked to the ...


24

I stumbled across this question, and while it is an old question and there are some halfway decent answers, I think it deserves a more in-depth response. I completely understand the question, which I think is am excellent question. Trying to understand the phases of the moon is much more difficult than most think. The short answer of it is that you cannot ...


21

Ignoring the "no gravity" part of your question - there is, it's 1/6th that of the Earth, the flag looks like it's "waving" because the horizontal pole that runs along the top of the flag got stuck part way out. This meant that the flag didn't "unfurl" fully and is hanging like a curtain rather than being stretched flat as was the original intention. The ...


19

I suspect the question may be unanswerable, and possibly even meaningless. As I understand it, the giant impact that resulted in the formation of the Moon would almost certainly have also completely liquefied whatever crust the Earth had at the time, producing a global "magma ocean". Thus, there would've been no traces of the impact left — or rather, ...


19

It just happens to be a coincidence. The current popular theory for how the Moon formed was a glancing impact on the Earth, late in the planet buiding process, by a Mars sized object. This caused the break up of the impactor and debris from both the impactor and the proto-Earth was flung into orbit to later coallesce into the Moon. So the Moon's size just ...


18

When we say that the Moon rotates, we don't mean relative to an observer on Earth, because we're also rotating. Maybe best is to think of it from the perspective of the Sun. If you were at the centre of the solar system, looking at the Earth, you'd see the Moon rotates once every 28 days or so. That also happens to be the amount of time it takes for the Moon ...


18

Officially, no -- but there is a weak case to be made that the Moon orbits the Sun rather than the Earth. If you trace the Moon's path in a Sun-centric frame of reference, that path is completely convex. Quoting this Wikipedia article: Unlike most other moons in the Solar System, the trajectory of the Moon is very similar to that of its planet. The ...


17

A "Trojan" object is any smaller object that shares the same orbit as a larger body but leads or trails it by about 60 degrees in the orbit. These positions are the L4 and L5 Lagrange points (respectively) in the larger body's orbit about its parent object. The L4 and L5 Lagrange points are locations of stable gravitational equallibrium between the larger ...


17

On the earth-sheltering question, the answer is yes, using material to increase the thermal mass of structures would work just as well on the Moon as on Earth. There might be minor differences due to different materials and lack of water in Moon soils but the general principal would still apply. As for the Moon's core still containing significant heat, ...


16

The two effects are not related. The size appearing larger is a matter of some speculation to this day, but it is purely a psychological effect. If you want to prove this, take a look a the moon while standing up and looking between your legs. It won't look nearly as large. The red/orange color is related to the sunset being red. In fact, it's the same ...


16

Let me try this way: the Sun isn't only pulling on the Earth, it's pulling on the Moon as well. The pull on the Earth is almost the same as the pull on the Moon, so the net effect of the Sun on the relative motion between the Earth and Moon is very small. Recall Galileo's law of motion: if you drop two objects close together from the same height, they ...


15

There is quite a bit. Here are the ones that come to mind immediately: Similar surface ages - The oldest rock on the earth and the oldest rocks returned from the moon are the same age. This implies similar creation time. Isotopic composition - The ratios of various atomic isotopes are basically the same indicating that the two bodies were created from ...


15

What you are seeing in those images is an ice halo. A halo is an optical phenomenon produced by ice crystals. Many can be observed while looking at the Sun or the Moon. To be precise, they are produced by the ice crystals in cirrus clouds high in the upper troposphere, at an altitude between 5 kilometres and 10 kilometres. The particular shape and ...


14

The Moon's orbit is inclined with respect to the Earth's orbit. In other words, if you imagine a Sun, Earth, and Moon model sitting on a tabletop, the Sun would sit approximately still and the Earth might slide around the desktop, while the Moon would orbit the Earth, hopping up off the table, and sinking back down into it. (I used to do this demonstration ...


14

(Source, Wikipedia Commons) The moon is generally called a "Harvest Moon" when it appears that way (i.e. large and red) in autumn, amongst a few other names. There are other names that are associated with specific timeframes as well. The colour is due to atmospheric scattering (Also known as Rayleigh scattering): may have noticed that they always ...


14

No, there is not a solar eclipse whenever we see a new moon. The reason we do not have a solar eclipse at every new moon is mostly due to the angle of Earth's axis (and by extension, the Moon's orbital plane) to the Earth-Sun line. See the diagram below (as requested) for a visual explanation. In the picture, the Sun is to the left. The upper image shows the ...


13

Well, I'd like to say that you are almost there. The key point of this question is to know that usually illustrations are just showing the relative positions but not with the real ratio. If the size and distance of the moon is the same as such pictures show, it will much harder to find when it lies at the same side of the sun. Because to see it, the ...


13

The Moon moves at about a thousand metres per second, but it's a long way away so it only appears to move slowly. Most of the apparent movement of the Moon is actually due to the rotation of the Earth. We see it appearing to go round the Earth once a day, but it actually takes about 28 days to complete an orbit. The Wikipedia article on the Moon's orbit has ...


13

As there wasn't a formal definition of a planet until recently, there still isn't one for a moon. But, a few guidelines: It should be in an orbit which is cleared of other objects, that is, not a bunch of objects in the same or very similar orbit. The typical minimum size for consideration is around a km. There is a smaller class known as moonlets that are ...


13

If you drop something into a pool of water, you will get a rebound effect in the middle where the object was dropped, and then waves will spread out around it. This rebound effect in the middle is the same phenomenon that causes central peaks in craters. The difference is just the scale: An impact that forms a >~15-km-diameter crater on the moon will ...


12

The problem with most of the earth-moon pictures is that they show the Earth and moon very close together - which suggests that the moon is in the earth's shadow for almost half of the time. So in the picture linked to above - it looks like a full moon should be dark. The real picture is more like this


12

As Ravachol quoted, the material on the surface of the moon is mainly the result of billions of years of micrometeorite impacts onto larger rocks on the lunar surface. We call this material "regolith" as opposed to "soil" because the latter term is used in geology to indicate a more biological/organic origin. "Regolith" should technically be used to ...


12

Your skepticism is well founded in this case. For a low orbit such as this, the leading perturbation will be from the mass concentrations (colloquially "mascons") in the Moon, which produce large variations in the gravitational field. The relevant timescale is probably weeks at best. The orbit of the Apollo 16 subsatellite PFS-2 decayed so rapidly that the ...



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