Last night we were driving, and my daughter looked at the moon through the clouds and said, “It’s cool how it looks like the moon is moving, but really it’s still, and it’s the clouds and us that are moving.” And I got to thinking about this. Obviously the moon is moving: it’s revolving around the earth. So who’s moving faster?
I challenged the moon to a race.
The moon pointed out the theory of relativity: all motion is relative. Faster acccording to what standard?
Since both of us are revolving around the same basic spot–the center of the earth–I suggested we use that as our basis. And I claimed victory: I complete a lap in 24 hours, whereas the moon takes 29 days.
But that’s not fair, the moon objected. THe moon’s on the outermost loop of the race track, and I’m on the innermost. I travel much less distance in 24 hours than the moon travels in 29 days.
So here’s my question: if we just calculate speed (relative to the earth’s center), who wins? And since it’s almost certainly the moon, by how much does it win? And is there some absurd assumption I’m making that makes this whole question invalid (other than the assumption that the moon would ever agree to race me)?
The moon’s average orbital speed is 3679 km/hr. The earth’s rotational speed is 40074 km / 24 hours = 1670 km/hr, so you will lose if you just stand still. But if you can run faster than 2009 km/hr you can win. But that’s just if you’re at the equator. If you stand near the north pole you can easily walk around it in a few seconds. However you’ll have to come up with a good argument that that meets the conditions of the race.
Next time, probably best to wait until the moon is drunk.
“Once we were all together you and the moon and I
But on the night you left me the moon raced back to the sky
Racing with the moon sailing thru the midnight blue
And then all too soon it’s lost from view
Gazing at the stars shining in the summer night
But just like the moon they fade from sight
In the blue heavens I see your face smiling at me
My heart will never be free until we’re back together
Racing with the moon that is what I’ll always do
Till I overtake the moon and you
Racing with the moon sailing thru the midnight blue
And then all too soon it’s lost from view
Gazing at the stars shining in the summer night
But just like the moon they fade from sight
In the blue heavens I see your face smiling at me
My heart will never be free until we’re back together
Racing with the moon that is what I’ll always do
Till I overtake the moon and you.”
And racing around to come up behind you again. 