# Thread: Why doesn't the sun pull the moon away from the earth?

1. ## Why doesn't the sun pull the moon away from the earth?

Since the gravitational force that the sun exerts on the moon is about twice as great at the gravitational force that the earth exerts on the moon.

2. pull away?

3. Originally Posted by Zombapocalypse
Since the gravitational force that the sun exerts on the moon is about twice as great at the gravitational force that the earth exerts on the moon.
It is? Source?

4. Pull away as in it would orbit the sun only instead of orbiting the sun-earth system.
It is? Source?
My physics textbook...this is a homework question and I can't come up with a good answer.

5. "the sun's pull only contributes as a centripetal force for its orbit around the sun. It doesn't actually pull the moon or the earth into it"

6. Probably would if we were dealing with a solar eclipse all the time. You gotta remember that the moon spins around the earth, so the sun pulls the two together as much as it pulls the moon away.

Amirite

7. maybe i'm dumb but wouldn't it have something to do with the fact that the earth is wayyyyyyyyy closer to the moon so the Sun's gravitational pull would be greatly reduced?

8. Ask yourself this: why doesn't the Sun's gravity pull the Earth into the Sun?

Same basic answer applies to the moon.

--

Edit: Also I don't think that the Sun is anywhere near as strong a gravitational force on the Moon as the Earth is.

9. The sun pulls both the earth and the moon around itself, which is the 365 day orbit. The 30 hour orbit of the moon around the earth is the lunar cycle caused by the earth's pull on the moon. It's 2 separate pulls.

10. Originally Posted by gouscfootball
The sun pulls both the earth and the moon around itself, which is the 365 day orbit. The 30 hour orbit of the moon around the earth is the lunar cycle caused by the earth's pull on the moon. It's 2 separate pulls.
That doesn't answer the question, though.

11. because the moon is much closer to the earth the sun can't break the moon away from the earths gravitational field.

12. Originally Posted by redbinder
That doesn't answer the question, though.
Earth's gravity is stronger than the sun's at this distance. The moon IS traveling further and further away though every year...something like 4 inches

13. Also I don't know if your teacher acknowledges centrifugal force (I mean, just put the moon, sun, and Earth into a closed system and it's right there, but some teachers get anal about it), but you could consider that. The Earth isn't pulled into the sun thanks to it's elliptical orbit, and the moon's orbit keeps it from colliding into us.

14. The moon does move away from the earth. About 1mm / year.

15. Actually to hijack this thread, anyone want to guess what the moon's orbit around the Sun looks like (if you were to draw it)?

16. Apollo pulls the Sun across the sky.

17. because the moon is mad alpha

18. due to newton's second law "if object a exerts a force on object b then object b will exert an equal an opposite earth on object a" the moon is actually continually getting further and further away from planet earth.. because of this we are never gonna have a total eclipse ever again as it will be too far away to block out the sun entirely..

interestin **** eh?

The attractive force of gravity is proportional to the mass of the two
objects in question and to the square of distance.

Mass of the earth: about 6 x 10^24 kg
Mass of the sun: about 2 x 10^30 kg

The sun's gravitational pull on the moon is proportional to 2 x 10^30
/ (1.5 x 10^8)^2 = about 8.8 x 10^13

The earth's gravitational pull on the moon is proportional to 6 x
10^24 / (3.84 x 10^5) = about 4 x 10^13

Sure enough, the sun pulls on the moon harder than the earth does!
Sounds crazy, doesn't it?

Consider the earth by itself - it would orbit the sun pretty much like
it does now. Consider the moon by itself - it would orbit the sun
pretty much like it does now. We say that the moon orbits the earth
because it's convenient. But it's more true to say that the moon
orbits the earth and the sun. The earth and the sun orbit the center
of our galaxy. The galaxy and the sun don't so much orbit as go
pretty straight (there's a mind-boggling amount of mass in a galaxy -
hard to change its direction!)

If you trace the path the moon makes in space, it's a spiral around
the sun. The earth also orbits in a spiral because of the affect the
moon's gravity has on our planet. Since the earth is rather more
massive than the sun, the moon moves more than the earth does in
response to the gravitational attraction the two share, but both
bodies orbit the sun.

19. The moon is moving away from the earth slowly. Srs, physicist here.

20. Originally Posted by Resplendency
due to newton's second law "if object a exerts a force on object b then object b will exert an equal an opposite earth on object a" the moon is actually continually getting further and further away from planet earth.. because of this we are never gonna have a total eclipse ever again as it will be too far away to block out the sun entirely..

interestin **** eh?

edit: if you want a calculation brah..

The attractive force of gravity is proportional to the mass of the two
objects in question and to the square of distance.

Mass of the earth: about 6 x 10^24 kg
Mass of the sun: about 2 x 10^30 kg

The sun's gravitational pull on the moon is proportional to 2 x 10^30
/ (1.5 x 10^8)^2 = about 8.8 x 10^13

The earth's gravitational pull on the moon is proportional to 6 x
10^24 / (3.84 x 10^5) = about 4 x 10^13

Sure enough, the sun pulls on the moon harder than the earth does!
Sounds crazy, doesn't it?

Consider the earth by itself - it would orbit the sun pretty much like
it does now. Consider the moon by itself - it would orbit the sun
pretty much like it does now. We say that the moon orbits the earth
because it's convenient. But it's more true to say that the moon
orbits the earth and the sun. The earth and the sun orbit the center
of our galaxy. The galaxy and the sun don't so much orbit as go
pretty straight (there's a mind-boggling amount of mass in a galaxy -
hard to change its direction!)

If you trace the path the moon makes in space, it's a spiral around
the sun. The earth also orbits in a spiral because of the affect the
moon's gravity has on our planet. Since the earth is rather more
massive than the sun, the moon moves more than the earth does in
response to the gravitational attraction the two share, but both
bodies orbit the sun.
All correct except for the assertion that the Earth and/or Moon orbit in a spiral around the Sun. A common misconception. If you were to trace the Moon's orbit around the Sun (not drawing the Earth's orbit at all) it would be almost a circle, but not. There are no loops or spirals.

Here is the orbits:

Earth (blue), Moon (purple)

21. Ah, wait, I get it. It's because of the conservation of angular momentum.

22. Originally Posted by redbinder
All correct except for the assertion that the Earth and/or Moon orbit in a spiral around the Sun. A common misconception. If you were to trace the Moon's orbit around the Sun (not drawing the Earth's orbit at all) it would be almost a circle, but not. There are no loops or spirals.

Here is the orbits:

Earth (blue), Moon (purple)

i thought it was clear that was copypasta brah lol.. i ain't writin out equations and **** for the misc..