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Moon-viewing question

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posted on Mar, 16 2011 @ 04:33 PM
Hey all,

So I definitely want to check out the moon. Around here we only get about 60 days of clear skies a year, and this weekend should be clear, so I don't want to miss it!

My question is: What time will it be the closest, early AM saturday or early AM sunday?

posted on Mar, 16 2011 @ 06:27 PM
reply to post by Schmidt1989

Actually, the distance is the same. On Saturday early AM, the Moon is approaching perigee (the closest point in its orbit to the Earth) and on Sunday early AM it has reached perigee and is moving away.

That said...

When it comes to distance, it doesn't really matter what time of the month you look at the Moon. At apogee (the farthest point in its orbit to the Earth) the Moon only looks a few percent smaller than it does at perigee. I've been looking at the Moon for 40 years, and I can't see the difference.

In fact, when I was running the numbers I remembered an interesting detail:
(Bear with me while I explain)

I have a 12" globe of the Earth on my desk.
Currently, it's turned so I am looking straight at the east coast of the United States.
Hawaii is just visible on the edge to the left, and Europe is just visible to the edge on the right.
From my chair, if I reach out, I can just touch Pennsylvania with my finger.
Hawaii & Europe are out of reach. That is because the globe's radius is 6 inches, so the center of the globe and the bits I can see on the edges are 6" further away from me than the closest part (that is facing right at me).

Now let's go full scale and turn this around:

This weekend is a full moon. Thus, the Moon will be high in the sky at midnight.
If you look at the Moon from Pennsylvania at midnight, the Moon will be high in the sky. However...
At that same moment, the full moon is setting in Europe, and rising in Hawaii.
Remembering the globe, the Moon is, at that moment further away from Europe & Hawaii than it is from Pennsylvania.
The Earth's radius is ~4,000 miles.
That means that the Moon is 4,000 miles further away when it is rising or setting than it is when it's straight overhead.
The Moon is - on the average - ~240,000 miles from Earth (center-to-center), so the change in distance from the surface of the Earth as the planet rotates 6 hours (one-quarter turn) is ~1/60th of the total distance between the two.

How does this relate to your question?

When you specified "early AM" Saturday & Sunday, I ran the numbers for each hour from midnight to 3am EDT. During those hours, the center-to-center distance from the Earth to the Moon changed by less than 100 miles (and, as I said earlier, was close to the same for both nights).

However, the distance from the surface of the Earth changed by almost thousand miles in those few hours, thanks to the Earth's size & rotation.

But still, the change in distance is insignificant to the total distance involved; so don't sweat it - Just enjoy the pretty full moon.

posted on Mar, 16 2011 @ 07:21 PM
Thanks bud, great post and a lot of help!

posted on Mar, 17 2011 @ 01:04 AM
reply to post by Saint Exupery

that was pretty damn impressive... you deserve a star...
you have a way of describing things thats... entrancing

posted on Mar, 17 2011 @ 11:00 AM

This may help some who want to stage a photo.

posted on Mar, 17 2011 @ 04:18 PM
Just wanted to add a little information.

Here is a perspective of the apparent size difference between lunar perigee and apogee.

And here is a great little animation that can be found on Wikipedia of the same. This rocking motion is called lunar libration.

edit on 3/17/2011 by Devino because: (no reason given)

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