Re: Help: Optics

From: Gregory L. Hansen (glhansen_at_steel.ucs.indiana.edu)
Date: 01/26/05 

Date: Wed, 26 Jan 2005 02:05:50 +0000 (UTC)

In article <41f6ef54$0$85557$cd19a363@news.wanadoo.nl>,
Kevin <kschaaps@rebootstation.dyndns.org> wrote:
>Greetings all,
>
>I am in desperate need of some assistance, and I hoped there would be
>someone here who would be willing to help me.
>
>At the present time, I am working on designing a solar system. Fortunately
>the basics are in fact quite simple. Now I am working on the moons
>surrounding a planet. And I got a bit sidetracked.
>
>I would like to find a way to calculate the optical size of an object (moon)
>taken at a certain distance.
>
>For instance:
>
>Distance Planet to moon: 384.410 km
>Diameter Moon: 3474 km
>When PersonX looks at the Moon the diameter of the moon appears: 10cm.
>
>I would like to find a way to calculate that 10cm.

Apparant diameter is not well defined. Apparant diameter compared to a
reference at what distance from the observer?

Angle is the usual parameter. One degree of arc is about a thumb's width
with your arm outstretched, the Moon spans about half a degree of arc.

  tan(theta) = diameter/length

For astronomical distances you have skinny triangles, tan(theta)~=theta.
Theta is in radians. 360 degrees in 2*pi radians. 

-- 
"Let us learn to dream, gentlemen, then perhaps we shall find the
truth... But let us beware of publishing our dreams before they have been
put to the proof by the waking understanding." -- Friedrich August Kekulé

Relevant Pages

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