General Question

Pied_Pfeffer's avatar

How many moons does planet Earth really have?

Asked by Pied_Pfeffer (22662 points ) May 25th, 2012

Is there only one?

Is it possible that there are two, as mentioned by Stephen Fry, host of QI in this clip?

A year later, Mr. Fry tosses in a curve ball to his QI panel by asking the same question, but stating the answer is that Earth has either one or five moons, depending upon whose viewpoint you believe, based upon new discoveries.

So, what is the true answer? What facts can you provide to back up your call on this?

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24 Answers

XOIIO's avatar

One. Facts? Science. Also, when it’s night look up. One.

Same as asking if the earth is flat.

Pied_Pfeffer's avatar

@XOIIO That isn’t enough evidence to convince me that you are right. Nor is Stephen Fry’s reports for that matter. This is why I am asking the question.

lillycoyote's avatar

@Pied_Pfeffer I don’t know if this is what they are talking about in the video you posted. Damn Brits! I don’t know what they are saying half the time! But Cruithne is apparently only a “qausi-satellite” rather than an actual satellite, which disqualifies from being an actual moon, and I don’t fully understand what difference is between a “quasi-satellite” and an actual satellite, though that lack of understanding may stem from my not actually having read the Wikipedia entry or having looked into it any further. :-)

Lightlyseared's avatar

There is one moon. Cruithne is not really a moon, because Earth and Cruithne are not gravitationally bound.
There are several theories about other moons but they are more along the lines of conspiracy theories than anything else.

WestRiverrat's avatar

It kind of depends too on whether you want to count man made objects as moons too.

morphail's avatar

by the usual everyday definition of the word “moon”, there is one.

Nullo's avatar

If you like, you can generalize ‘moon’ back to ‘satellite’ and lump in every bit of the stuff that we’ve thrown up there in the last several decades that hasn’t come back down. It’s actually becoming a problem, since the bits don’t all travel at the same speed. The shuttle program went through 80 or so windows during its run. We stand on the brink of the pieces breaking up into smaller pieces, denying space to everyone. Hollywood, that’s your cue for a decent movie!

Pied_Pfeffer's avatar

@RareDenver The link didn’t work, however, I took your advice.

Here is one article found on a second moon.

Edit: I just noticed the source and read the comments. I’ll keep looking for a more reliable source.

Response moderated (Unhelpful)
Response moderated (Unhelpful)
gondwanalon's avatar

If you want to call Cruithne another of Earth’s moon’s then that is your prerogative. However as I see it, Cruithne is just a relatively very small asteroid. Compare Cruithne’s 5K in diameter to that of the largest known asteroid “4 Vesta” which is 525K in diameter.

There are perhaps millions of asteroids orbiting the Sun. Count them all as Earth’s moons if that pleases you.

Pied_Pfeffer's avatar

@gailcalled When I think of legitimate celestial mechanics or solar geologists, the first name that pops into my head is Stephen Fry. Then you are the only one. Even Stephen Fry wouldn’t claim this. Now please go sit in the ‘Unhelpful’ corner with @XOIIO.

@gondwanalon There is no prerogative here other than to find out why the multiple moons question was asked.

There are perhaps millions of asteroids orbiting the Sun. Count them all as Earth’s moons if that pleases you. Now, that’s just silly on more than one level.

gondwanalon's avatar

It wasn’t my intension to be silly. I was trying to be helpful.

Back in the 1970’s I read the following poem that was written by a kindergarten student. It stayed with me all these years:

The Moon, Moon
The Moon, Moon, Moon
Is a Moon

Perhaps the Earth’s Moon, poetry and silliness are in the eyes of the beholder.

gasman's avatar

Stephen Fry has a reputation as a skeptic, so I wasn’t sure what to make of it. But Wikipedia (Google, too) to the rescue again:

3753 Cruithne is an asteroid in orbit around the Sun in approximate 1:1 orbital resonance with the Earth. It is a periodic inclusion planetoid orbiting the Sun in an apparent horseshoe orbit.[2] It has been incorrectly called “Earth’s second moon”, but it is a quasi-satellite[2], not a moon. Cruithne does not orbit Earth, and at times it is on the other side of the Sun.[3] Its orbit takes it inwards towards the orbit of Mercury, and outside the orbit of Mars.[3] Cruithne orbits the Sun in about 1 year, but it takes 770 years for the series to complete a horseshoe-shaped movement, with the Earth in the gap of the horseshoe.[3]

The term 1:1 orbital resonance is explained here? The bodies interact in a way similar to pushing a kid on a swing once per period. It’s not stable long term, but Wikipedia reassures us: There is no danger of a collision with Earth for millions of years, if ever. Wikipedia cites its discovery in 1986, not 1997 per Fry. It’s only 3 miles across and fainter than Pluto.

Good line by one of the panelists: “It’s called THE moon. I rest my case.”

Response moderated (Unhelpful)
Pied_Pfeffer's avatar

@RareDenver Thank you for your diligence in providing a link to a helpful website.

@All: Thank you all for your assistance with this. Brian Cox has not returned any of my calls, so your help in this matter is greatly appreciated.

This is not the first time that Stephen Fry and the QI researchers have been wrong. Mr. Fry usually comes back with a correction when he and the team are proven wrong. Thus this question.

josie's avatar

There is only one.
FYI, I just got finished working out and I am not wearing my glasses. When I first read the question, I thought it said “How many morons does planet Earth really have?”
Interesting

Response moderated (Off-Topic)
Response moderated (Off-Topic)
augustlan's avatar

[mod says] Please remember: This question is in the General Section. Responses must be helpful and on-topic.

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