# Thread: What if the moon disappears? ;)

1. Newbie
Join Date
Sep 2003
Posts
7
Lets assumes that you wake up one morning and turn on your TV to find that the moon has dissapeared. You immediately start wondering what will happen to the Earth now that the moon is gone. Now my question to you is what would happen to Earths rotational velocity if the moon were to have flown away? Is the Earths rotational velocity increasing, decreasing or staying the same as the moon moves away from the Earth?

2. IonDrive Guest
Actually the moon&#39;s gravity effects work to decrease earths rotational speed over millions and billions of years. For example, examination of coral reefs from the cambrian era has shown that days were considerably shorter at that time, something like 23 hours or less, resulting in one year having about 400 days. (Please ask a palaeontologist or some dude from a similar area for details. )
So if you took the moon away, a day&#39;s length would simply stay at 24 hours forever (maybe a little differing due to sun&#39;s tidal effects on our planet), instead of being 25 hours in a few hundred million years, then 26 hours and so on.

The actually bigger effect would be caused by the fact that earth would keep the tangential speed vector with which it now circles the common mass center of the earth-moon system, which would result in, depending on which point of it&#39;s way around earth you would make the moon disappear, some slight increase or decrease in the eccentricity of earth&#39;s orbit around the sun. But very slight indeed, since the mass center of earth and moon still lies somewhere WAY below Earth&#39;s surface.

And since I very much dislike spherical geometry, I am not going to do a lenghty calculation here about how much the eccentricity of Earth&#39;s orbit would change. B)

3. Member
Join Date
Jul 2003
Posts
32
If I&#39;m remembering my orbital dynamics class correctly, and I might not be, Earth&#39;s angular momentum is decreasing since Luna is currently getting farther away. But at some point in a few trillion years things will reverse and the moon will start getting closer until it collides with Earth. By then Sol should be a gas giant and will already have swallowed most of the inner planets so it won&#39;t really matter.

4. Luddite, have you been watching Space: 1999 again???

5. Planetwatcher Guest
At the risk of an arguement, I&#39;m gonna quote the Bible on this one.

Mark 13:23 But take ye heed: behold, I have foretold you all things.
24 But in those days, after that tribulation, the sun shall be darkened, and the moon shall not give her light,

I know I won&#39;t be around for that, nor would I want to be. I will be watching however from a very safe distance, and I mean to tell you, if you turn on your TV to that, what&#39;s going to happen to Earth is the very least of worrys, because that&#39;s going to be right in the middle of all hell breaking loose. Literally.

6. The Pope Guest
I thought that was meant to happen in the year 2000?

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