BSA Astronomy Merit Badge

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Pete
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BSA Astronomy Merit Badge

Unread post by Pete » Mon Nov 07, 2016 9:27 pm

Nov 7, 2014 Tonight's conditions were perfect for hosting scouts from Barrington scout troop #2 – 19:00 – 20:30

We started out with lasering constellations. Then viewed Brocchi’s Cluster (the Coathanger) with mounted 15X70 binoculars. Each scout then viewed Luna through a 3” Dob (built by Kenny Concca) before we repaired inside the observatory. Targets included Luna thru polarized filters at 115X and 180X, Neptune at 180X, Albireo as 115X, M15 at 180X, M57 at 180X, and M31/M32 at 115X.
2 leaders and 9 pretty well behaved very interested scouts.

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Hand held shots from my pocket Canon not as good as they usually are but they tell the story.

Pete 7 Nov 2016
Pete P.
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Re: BSA Astronomy Merit Badge

Unread post by Apollo XX » Tue Nov 08, 2016 8:44 am

Nice, Pete! Looks like it was a good time for them. 8)
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Pete
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Unread post by Pete » Tue Nov 08, 2016 11:49 am

Yeah, but I've really gotta figure out how to turn on the camera's image stabilization :-(

Tonight we're going to take a first shot at measuring the height of the lunar mountains.

Pete
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Unread post by Apollo XX » Tue Nov 08, 2016 2:13 pm

Pete wrote:
Tonight we're going to take a first shot at measuring the height of the lunar mountains.

Pete
I'm looking forward to hearing about that.
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Unread post by Pete » Tue Nov 08, 2016 2:29 pm

Galileo measured the height of lunar moons at quadrature. We'll be about 16 hours late, but shadows cast on a sphere can be complex and I'm a simple kind of guy. Maybe we can concentrate on the equator???

FWIW, tonight looks like a good night for early stargazing. Before we all do political damage assessment.

Pete
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Re: BSA Astronomy Merit Badge

Unread post by Apollo XX » Wed Nov 09, 2016 8:32 am

Hi Pete,

I was out both last night and the night before (when you were hosting the boy scouts). I spent a significant amount of time on the moon on both nights, and it seemed like Monday's phase (1st Qtr) would've been the better of the two. On Monday there were long shadows from the mountains around and in Imbrium, but last night the terminator was virtually void of any mountain shadows or if there were they were so short as to be very difficult to measure. The Jura's are coming up, but as you mentioned the curvature would really factor in with those being on the far side of the curve.
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Re: BSA Astronomy Merit Badge

Unread post by Stargrrl » Wed Nov 09, 2016 9:43 am

Hi Pete, if you do measure moon mountains, please write up a "how to" post - be really interested in knowing how this is done - Rebekah
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Unread post by mrgizmo65 » Wed Nov 09, 2016 8:22 pm

Very nice report Pete and it looks like your young guests were very attentive and interested in your "toys" Thanks for sharing it with us, btw great photos
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Re: BSA Astronomy Merit Badge

Unread post by AndyG » Fri Nov 11, 2016 4:26 pm

The angle between the mountain and the terminator is the altitude of the sun above the horizon. At the terminator the sun is right on the horizon at the mountain and 90 degrees from the terminator the sun is at zenith.

The shadow as seen from earth is foreshortened based on the longitudinal angle between the mountain and the limb (no foreshortening at 90 degrees from the limb, face-on; shortened to 0 right at the limb).

We can get the mountain height by finding the longitudinal angles between a) the mountain and the terminator and b) the mountain and the limb. (a) gives the sun's altitude at the mountain, and (b) gives the foreshortening factor.

I worked out some of the geometry and here's a spreadsheet with the calculation. I marked-up Mike's daytime photo guessing the location of the terminator and the limb. If you load the image into a program like MS paint, photoshop, or gimp, you can read off the pixel coordinates of a mountain and measure the width of a shadow and plug the values into the spreadsheet and read out the height of the mountain. The results seem plausible giving mountain heights of 1-2 km.

Image

I can post the details of the geometry if anyone is interested.
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Re: BSA Astronomy Merit Badge

Unread post by Pete » Fri Nov 11, 2016 5:30 pm

There are spherical geometry calculations available both in my astro experiment books and online. It gets complex if you're not at quadrature and on the equator. Would prefer that the student figure out how Galileo did it and develop the calculations himself but he's free to attack this any way he wishes. Have emphasized that it's his project and I'm cool with whatever, but since he's interested in a career in astronomy colleges will be more impressed with his working out calculations that may be more approximate than accurate but are indeed self derived. Variables include angle of the Earth as well as angle to the sun, and position on the spherical surface of Luna. Makes my head spin, but in a good way.

Andy, did you write that spreadsheet yourself?

Pete
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