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Guaging the size of the moon


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Hi guys,

My first question thread :)

I think this is the right place for this.

Anyway, I've not seen anything around on this topic.

What I want to know is, when I'm looking at the moon through a telescope, how can I judge how big certain features are.

I think the best way for this would be knowing how big something is that I can look at as a reference of size. I'm not after exact measurements, just a general idea to make the experience better.

I'll post below a picture (rather poor) I took last night, I'm not sure what part of the moon this is (it's really smooth with only a few craters) but hopefully somebody can tell me the size of the craters? That way I can use the mental image I have as reference for the rest of things I look at.

If not, maybe an exercise for me to find something that people know the size of?


Sorry for the poor quality but this is my first moon pic.

Thanks and I hope this isn't a stupid first question :D

Edited by Beano
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hi there

no questions are stupid - unless you don't ask them!

in all honesty, the photo is showing no features as such as it's out of focus and over exposed. If you were to look at the moon through the scope you'd see hundreds if not thousands of features in this area.

here's an example of a moon map Moon Map: Moon Map Photos, Wallpapers, Galleries, moon map

At the top you can see the Plato crater. This is 100km across the longest axis.

You can get a lot of information from Wikipedia too eg http://the-moon.wikispaces.com/Lunar+100

hope this helps.

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Thank you for the links and advice. The picture is quite poor compared to what I could see through the scope.

I'll make the Plato my next mission for the next clear night now I know the size.

The Wiki link will help lots too. I will get a list of things to look at ranging in sizes.

Thanks again!

Edited by Beano
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I think one way would be to use well known features on the moon to give a sense of scale. For example the crater Tycho is around 85km in diameter, Plato is 109 km across, Copernicus 93km etc, etc. The famous Straight Wall fault is around 120km in length while the crater Birt which lies close to it is 17km in diameter.

If you are viewing something in the same field of view as one of these well known features then at least you have something to give some scale to the view.

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Observing the Moon just gets better and better the more you learn about it. I use the free software 'Virtual Moon Atlas' from en:download [Virtual Moon Atlas]

Just click on any crater or other feature and it tells you what it is with information about size etc. It will also pick out the Apollo landing sites. When the moon is bright like it is now you can get a good photo with a 1/1000 or 1/500 second exposure. You just need to experiment a bit with exposure times and ISO settings.

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Thanks for all of your advice. It will help a lot. I can't wait to get a good look now.

I was going to get looking tonight but before I got chance to get the telescope out a thin haze came over making the moon blurry. Always the case it seems.

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