How can the moon do that?

How can the moon possibly stay in orbit around our planet? The chances of some random hunk of rock orbiting us at exactly the right altitude and speed to counter the effect of gravity are just amazing, no? Or is there a massive margin for error?

But, I mean, how many planets have moons? How many stars have planets? The chances of this happening perfectly - or at least to within 3 cm a year as far as I can remember - must be astronomical. And yet it's happening all over the place!!

At the very least, the moon should be flying away from us at 100 kilometres an hour, but it isn't. How can it slot into that exact place at the exact right speed and all that?

I would think the chances of that happening are about 4 X 19 to the power of 40 or something; but I'm sure the answer is very simple, like it has happened that many times and the ones remaining are just the success stories, but I dunno . . . there sure seem to be a lot of success stories.

I will retire in this state of mind.

How?

Physics. Gravity. The laws of nature and the universe.

What blows my mind is how the moon seems exactly the size of the solar disc during an eclipse.

I can understand why the moon is in orbit and all of that...but how is the moon just the right size and distance from the earth to allow this phenomenon?

I'm sure Commanderkeenkid has an explanation...

It is actually breaking orbit and getting away from us inch by inch..
It,ll takes millions of years though

Also why does the moon not spin? Its same side always faces the earth. Does this happen anywhere else in our solar system?

the moon spins, it just spins at exactly the right speed to always present the same face.

What I find interesting is how nobody spotted the satellites of the other plantes until recently in our solar system. Yet ancient tribes in africa knew of them 1000's of years ago such as the dogma tribes.

hey now, we'll have none of that hate speech around here, buddy!

Originally posted by 25cents
the moon spins, it just spins at exactly the right speed to always present the same face.

and what are the chances of that?

slim to none. but that's pretty much the story of our planet.

Originally posted by tim_dorset_uk
What I find interesting is how nobody spotted the satellites of the other plantes until recently in our solar system. Yet ancient tribes in africa knew of them 1000's of years ago such as the dogma tribes.

I think you meant the Dogon tribes...

www.crystalinks.com...

Astronomy

The Dogon are famous for their astronomical knowledge taught through oral tradition, dating back thousands of years, referencing the star system, Sirius. Sirius is the dog star. It is linked with the Egyptian goddess Isis. The astronomical information known by the Dogon since that time, was not discovered and verified until the 19th and 20th centuries, making one wonder how the Dogon came by this knowledge. Their oral traditions say it was given to them by the Nommo. The source of their information may date back to the time of the ancient Egyptian priests.

The Dogon priests said that Sirius had a companion star that was invisible to the human eye. They also stated that the star moved in a 50-year elliptical orbit around Sirius, that it was small and incredibly heavy, and that it rotated on its axis.

Initially the anthropologists wrote it off publishing the information in an obscure anthropological journal, because they didn't appreciate the astronomical importance of the information.

What they didn't know was that since 1844, astronomers had suspected that Sirius A had a companion star. This was in part determined when it was observed that the path of the star wobbled. In 1862 Alvan Clark discovered the second star making Sirius a binary star system (two stars).

In the 1920's it was determined that Sirius B, the companion of Sirius, was a white dwarf star. White dwarfs are small, dense stars that burn dimly. The pull of its gravity causes Sirius' wavy movement. Sirius B is smaller than planet Earth.

The Dogon name for Sirius B is Po Tolo. It means star - tolo and smallest seed - po. Seed refers to creation. In this case, perhaps human creation.

By this name they describe the star's smallness. It is, they say, the smallest thing there is.

They also claim that it is 'the heaviest star' and is white in color.

The Dogon thus attribute to Sirius B its three principal properties as a white dwarf: small, heavy, white.

There's lots been written about this tribe since I remember reading about them decades ago. I'm not sure how much was truth and what was conjecture, but they did have a knack for Sirius astrology.

For a thorough and fascinating possible explanation of how the moon was placed in orbit around the earth by ET's please read chapter 10 of the Ringmakers of Saturn by Norman R. Bergrun. Mr. Bergrun worked for many aerospace companies including NACA throughout his 40+ year career including Lockheed Missile & Space Company 1956-1968.

For a thorough and fascinating explanation on how orbits work, you can always read wikipedia:
en.wikipedia.org...

So to answer your question, no, the velocity and position of the moon don't have to be exactly as they are to fall into orbit around the Earth. Something with a different velocity/position would be in a different orbit, but it could still be in a stable elliptical one as it is now.

The reason why the moon only faces one of its sides to the Earth is because of tidal locking, a phenomenon in which the Earth's gravity pulls stronger on the moon's closer side (since it's less distant from the Earth) than on the farther side, eventually stopping the moon's rotation in relationship to the earth. Thus, the moon takes the same time to rotate about its axis as it does to orbit around the Earth. Tidal locking is demonstrated in many other moons in the solar system, especially ones that are close to the planets they orbit.

Also it's no coincidence the moon is where it is.

Current theories suggest the moon formed in Earth orbit early in the history of our planet, when a planetoid roughly the size of Mars crashed into the Earth. Much of the debris from that collision ended up in Earth orbit, where it accumulated and formed the Moon we know today. That's one explanation for the Moon's low density and lack of a large iron core, the Moon is basically made of lighter stuff from the crusts of both Earth and the body that collided with it.

Much the opposite is Mercury, which IIRC is the densest object in the Solar System. Although about the same size of the Moon, most of Mercury is a large ball of iron.

[edit on 7/30/06 by xmotex]

watch the rocks
The chances of this happening perfectly - or at least to within 3 cm a year as far as I can remember - must be astronomical.

Why?
The planets form as dust rotating about the sun. All the material that didn't "perfectly" get captured around a 'permanent' moon like orbit will just accrete onto the planet. Where the laws of gravity allow something like a moon to accrete along with the planet, you will then have a moon.

However, earth's moon is slightly different, because the its moon formed after earth itself was impacted, material was ejected into space. Some undoubtedly returned to earth, and the parts that happened to be in a stable place, remained such.

Originally posted by masqua
What blows my mind is how the moon seems exactly the size of the solar disc during an eclipse.

Its not. It only appears that way. The only part of the eclipsing moon that you would see is the part eclipsing the sun, not the rest of it. Because the moon appears as a circle, the part that you see is also a curve.

xeros
Also why does the moon not spin?

It rotates, but its rotation about its own axis, I think, is canceled out by its revolution about the earth, thus only one side is apparent from earth.

and what are the chances of that?

Why do you think it has anything to do with chance. If you think its immpossible, look at the equations for the graviational relationships between them and please show us why it shouldn't be happening.

tim dorset uk
Yet ancient tribes in africa knew of them 1000's of years ago such as the dogma tribes.

I beleive you are thinking of the Dogon tribe in Africa. They had no knowledge of other moons on planets within this solar system. What they are famous for is the claim that they knew about Sirius, which is a trinary star system, but appears as a single point of light to the naked eye. They, infact, have no knowledge of it as any sort of system. People studying the Dogon saw some of their rock drawings, and decided that that was what they represented. IOW, it was the interpretation of the explorers, not the Dogon.

regarding the size of the moon to the size of the sun

Originally posted by Nygdan
Its not. It only appears that way. The only part of the eclipsing moon that you would see is the part eclipsing the sun, not the rest of it. Because the moon appears as a circle, the part that you see is also a curve.

www.space.com...

"The Sun is far larger than the Moon -- about 400 times larger in diameter," explains James C. White II, executive director of the Astronomical Society of the Pacific. "Yet a happy circumstance is that the Sun is also about 400 times farther from the Earth than the Moon."

This makes the Moon and Sun appear roughly the same size in the sky. When the Moon's orbit about the Earth takes it directly between the Sun and us, the Moon can obscure all or part of the Sun. Exactly what happens depends on minor changes in distance and position.

*bolding mine

It's the bolded "happy circumstance" I'm referring to. It's almost too pat, as if the moon was 'placed'.

When the moon was still new,it filled up half the night sky,but every year is it inches farther away. We wouldnt be here without the moon. The moon slowed the rotation of the earth after it was hit by the planet(if you go with this theory),and stabalizes the earth on its tilted axis.

Yes, I do have some answers, but a lot of them have already been said... And it's late, and I just spent all weekend in the great outdoors enjoying myself... Before I digress further, though, I do feel the need to comment on the notions that Luna may have been placed in its orbit...

Firstly, keep in mind that it hasn't always been where it is now. As people have said, it moved farther away every year, at a rate of about 1 cm per year. So, for example, 5 million years ago it would have been 50 km (31 mi) closer. Sure, that may not seem like a lot, but a minute change like that would have drastic effects on eclipses, tides, the rotation of both bodies, and much more.

As for the tidal lock of Earth and Luna, it is a pretty neat thing, though not rare. For example, look at Pluto and Charon. They're tidal lock is so strong that not only does Charon have the same face to Pluto, but its rotation around Pluto is exactly the same length as Pluto's day - meaning that Charon is always in the same spot in the sky above Pluto.

EDIT TO ADD 24 HOURS LATER:

That's what I get for thinking while I'm tired... I mistakenly said that the Moon is moving away at a rate of 1 cm/yr. What I should have said was 3.8 cm/yr. So, 5 mya Luna would have been about 118 miles closer. I'm surprised no one had caught my error yet!

[edit on 7/31/2006 by cmdrkeenkid]

I was just arguing about this with a few mates today, and we agreed that either it must have happened so many times that what we are left with are the orbits that worked, or that there must be some massive margin for error that allows such an orbit to take place.

But after reading my somewhat hijacked thread, I feel like slapping myself on the forehead. That dust and debris explanation is so obvious!!! I mean, it can happen that many times and what we are left with are the ones in a good orbit. But I am glad I finally cleared that up. I'll pop back in tomorrow and impress them all with my knowledge . . .

But how much did the formation of the moon affect Earth's orbit around the sun? Going from a few equally spread out dust particles to a single massive body swinging off you is no easy transition, especially when you're delicately orbiting around a fusion reactor. Was it possible that the moons formation stopped this planet from falling into the sun, or something>?

Much the opposite is Mercury, which IIRC is the densest object in the Solar System. Although about the same size of the Moon, most of Mercury is a large ball of iron.

Actually, Earth's density is fractionally higher than that of Mercury.