2 moons

[hopalong]

If the Earth had 2 moons what effect would it have on Earth?

[bernardo]

The main effect of the Moon on the Earth is to produce tides (a high tide in the bit nearest the moon, another high tide on the other side of the world, and low tides in the bits in between.  There are two tides per day (approximately) in any one place, because of the Earth rotating underneath where the Moon is, and the high tide follows the Moon around the Earth.

 

If there were 2 moons, each moon would have the same effect.  If the 2 moons were at 90 degree angles to each other, the tides would cancel out with each other; if the 2 moons were at approximately the same angle (or opposite each other) then the tides which they produce would add together and make an extra big tide.

 

The cycle of tides coming in and out is an important part of the life of many creatures near the shore-line, so the existence of two moons would have made animals and plants evolve in a different way, dealing with more complex daily patterns of when and where the water is going to be.

[delapeyre64]

Nice answer just add the sun into it. if we had two moons 180 degrees apart on either side the same mass and orbit. All thats left is the sun  and other astral bodies so their would be a tide but quite mild.Interesting to look at evolution as it shows how long our moon has been there.

[QmunkE]

Two moons could also influence the geological stability of the planet, i.e. the tides in the molten mantle below the crust. It might even be conceivable that conditions would be so different that life might never have evolved to this state, being made completely uninhabitable by volcanic activity, earthquakes and the corresponding releases of noxious and greenhouse gases.

[Dagman]

We have in fact got 5 moons, though four are pretty small in comparison, however it's true! Not an answer but Qi.

[bernardo]

5 moons?  Really?  Do you mean 5 natural moons, not counting artificial satellites?  I have never heard that before.  What are the details?  Where are they?  How far away? How big?  Presumably the other 4 are really tiny, otherwise I would have heard about them already.

[QmunkE]

bernado, you should watch QI. A marvelous source of interesting if completely useless facts. Alan Davies was caught out by this question twice - three new "moons" were discovered between his being asked the first time and then again next series.

[bernardo]

I do usually watch QI but I don't remember anything about more than one moon for the Earth.  Do you know the details?  I did a bit of googling but I only found anecdotal Chinese-whispers rather than any reliable information.

[QmunkE]

Well, the following link shows the two moons originally quoted that caught AD out the first time:

http://en.wikipedia.org/wiki/Natural_satellite

Cruithne is the name of this "moon"

[QmunkE]

Found a third one.

http://www.exo.net/~pauld/activities/astronomy/threemoon s.html