Earth v. Moon

**bcmarshall** · Nov23-09, 01:45 PM

Originally Posted by Sorry!

Here is the moon from India:

and from I believe Australia:

I am certain from the way you've described seeing the moon from your position that you have probably never seen the moon like this before.

Thanks for the pictures. They are very enlightening indeed, and you're right, I've never seen the moon like that before. What's even more interesting to me is that India is still in the Northern Hemisphere!

Thanks.

**bcmarshall** · Nov23-09, 01:55 PM

Originally Posted by DrGreg

The attached diagram shows how the angle between the moon and the observer's vertical varies at different times as the Earth rotates.

Photo credits:
Earth: Visible Earth, NASA.
Moon: Kopfjäger (Away) on flickr, CC BY 2.0

Good diagram, and thank you. I'm finally starting to see the mechanism involved, and the rest sort of clears itself up. I appreciate the answers.

**bcmarshall** · Nov23-09, 02:03 PM

Originally Posted by jambaugh

Think about it this way. Suppose you are standing on the Moon at the point nearest the Earth. Thus the Earth is directly overhead of you. You lay on your back to see it clearly. Now on your back you can rotate so the "half-Earth" appears in any direction you like. Right?

Now pick and orientation you want to view the Earth. As you lay on your back on the Moon I walk in the direction your head is pointing until I'm a quarter way round the moon. I'll be standing up but oriented exactly as you are laying down and I'll see the Earth's phase at the same random orientation you chose when you laid down.

It is a matter of relativity of orientation. Forget the moon is there and imagine you are floating in space. Pick the orientation you want to observe the Earth and then imagine the Moon appears below your feet.

Great explanation. Thanks to all of you. It was enlightening for me.

BTW, I lost the bet with my friend. That sux!

~~Sorry!~~ · Nov23-09, 02:05 PM

I don't think the moon in India is always so prominently horizontal, I'm not sure though finding images of the moon from placess other than America is pretty difficult I'm finding :P

**jambaugh** · Nov23-09, 02:21 PM

Originally Posted by bcmarshall

BTW, I lost the bet with my friend. That sux!

Small price to pay for greater knowledge. (Or was it small? How much did you loose?)

**bcmarshall** · Nov23-09, 02:32 PM

Originally Posted by jambaugh

Small price to pay for greater knowledge. (Or was it small? How much did you loose?)

Actually the only thing injured is my pride. I have to stand before the whole forum and say, "I'm not smarter than a 5th Grader!"

Oh well, could be worse...I think!

**bcmarshall** · Nov25-09, 03:01 AM

Since I started this thread, I spent a lot more time observing the moon and I realize that my assumptions about vertical shadows are completely incorrect. Even outside my own house tonight was a perfect example of how wrong that was. I took a photo, blurry because of a lack of tripod, but still clear enough to make my point.

My question now relates to this famous picture of Earthrise.

What mechanism would make the illuminated portion of the Earth at the top, and the illuminated portion of the Moon at the bottom?

Thanks again.

**Vanadium 50** · Nov25-09, 04:03 AM

Originally Posted by bcmarshall

What mechanism would make the illuminated portion of the Earth at the top, and the illuminated portion of the Moon at the bottom.

Where is the sun? That will answer the question of why objects are illuminated the way they are. Always go back to that and you'll be fine.