How long does it take for Earth to orbit Moon as seen from Moon's perspective?

[Nicholas Kang]

Hello

 

I am working on an orbit trajectory plot tool with my friend from the US. I have some question to ask all of you about this question.

 

In our trajectory plot, we would like to fix Moon as the center of our orbit plot. Then, from our perspective (the moon), what would the Earth's orbit be or look like?

 

From the moon's perspective, would the Earth seems like orbiting the Moon? If this is the case, how long does it take for Earth to "orbit" the Moon? The same period as lunar's orbit, i.e. 27 days?

 

Thanks for answering.

 

Nicholas.

[Argent]

I think there are two answers to this. The simple answer is that the Earth would just sit there in a boring, fixed position in the sky. Since the moon keeps the same face towards the Earth at all times the Earth won't appear to do anything.

 

The more complicated answer is that the Earth will move slowly from left to right and up and down like a Spirograph plot. This is because the moon does not keep precisely the same face towards the Earth all the time, but "wobbles" in a consistent way. I have seen some great animations of this online and will try to find one to post here for you.

 

Here is a link showing how the moon's appearance changes as seen from the Earth. You can imagine how that would impact the view of the Earth seen from any point on the Earth facing side.

Edited March 8, 2017 by Argent

[Nicholas Kang]

Ok, I think I need to further clarify my case. I don't mean someone just sits on lunar surface and watch Earth wobbling. I mean, get yourself up and high away from lunar surface and stay idle there, see how Earth moves around the Moon. In my test, it does "orbit" around the Moon this way (Moon is observer, Sun is focus, hence Earth is moving):

 

 

 

Then, Earth to the right

 

 

 

And finally it is between moon and Sun

 

 

 

Closer view:

 

 

 

Earth is missing which proves that it is really between Moon and Sun.

 

 

 

Then, Earth to the left

 

 

 

And finally back again (Moon between Earth and Sun). Earth completes one "orbit" around the Moon. Earth does not cover the Moon because Moon is not coplanar with the ecliptic. (That's why you don't have solar and lunar eclipse every months. They only happen when they are collinear.)

 

 

 

Here is the orbit plot diagram that I mentioned. My friend told me the white line is Earth's orbit plot. So, I want to know whether the orbit plot diagram is correct or not. In my case, I want to get from low lunar orbit to Earth-moon Lagrange point 1, so the yellow circle is the Moon and the green line is my planned trajectory, but I wonder what the white line is. My friend said that is Earth's trajectory as seem from Moon. So I want to know if that is really the case.

 

And if he is correct, what is the orbital period of Earth around the Moon as seen from the Moon then?

 

 

 

 

Thanks for answering.

 

Nicholas.

Edited March 8, 2017 by Nicholas Kang

[Argent]

Yes, I completely misunderstood what you were trying to do. I think the answer you are looking for is above my pay grade. I shall wait with interest to see what others have to say.