BSA Astronomy Merit Badge

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AndyG
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Re: BSA Astronomy Merit Badge

Unread post by AndyG » Fri Nov 11, 2016 6:13 pm

Pete wrote:It gets complex if you're not at quadrature and on the equator.
actually, it's not that bad (see description above)
Pete wrote: Andy, did you write that spreadsheet yourself?
yes. It calculates the geometry I described above :idea: I'd be glad to elaborate, but I did not think most people reading would be interested in the geometry/trig.
Andy
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Apollo XX
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Re: BSA Astronomy Merit Badge

Unread post by Apollo XX » Sat Nov 12, 2016 12:59 pm

Andy, wouldn't the shadow length be affected by the curvature of the sphere, ie; perhaps lengthened ahead of 90* and shortened beyond 90* or am I missing something with regards to the perspective we're looking from, or a compensation that the longitudinal angle calculation provides? I can't quite resolve it yet. My brain is in overdrive. 8)
Mike M.
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AndyG
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Re: BSA Astronomy Merit Badge

Unread post by AndyG » Sat Nov 12, 2016 3:08 pm

Apollo XX wrote:wouldn't the shadow length be affected by the curvature of the sphere
Good point, the shadow is lengthened as the curvature causes the surface to "drop away" compared to if the moon were flat, and the spreadsheet does not account for that. When the width of the shadow is small (less than ~1 degree of longitude), the error is negligible. For example, the crater near the equator has a shadow width ~ 0.4 degrees of longitude, and the spreadsheet under-estimates the height of the mountain by ~ 42 meters. When I get a chance, I'll update the spreadsheet to account for the curvature, but for now it should still be valid as long as the shadows are "short" relative to the moon's diameter.
Andy
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