[amsat-bb] Re: Width of the Earth's penumbra

Greg D. ko6th_greg at hotmail.com
Fri Sep 30 21:18:47 PDT 2011

The ISS isn't going straight through the Penumbra, top to bottom, but rather diagonally through it.  Neglecting that the ISS isn't going in a straight line either (it's an arc), the 8-ish seconds are the hypotenuse of the triangle.  We still don't know the height.

I wonder if we can figure out more about the shape of the Penumbra by looking at the transit times for satellites at different elevations?

Sorry, this is starting to make my head hurt,

Greg  KO6TH

> Date: Fri, 30 Sep 2011 23:17:08 +0100
> From: g7hia at btinternet.com
> To: amsat-bb at amsat.org
> Subject: [amsat-bb] Width of the Earth's penumbra
> This bb never fails to amaze me with how helpful folks can be.
> It was G0SFJ's postings about ARISSAt-1 MET time which set me thinking about the 
> width of the half shadow (Penumbra) experienced by the satellite before and 
> after eclipse.
> I was pointed to the simulation option in the satellite tracker Orbitron 3.17 
> which shows the selected satellites Eclipse condition 
> No, Penumbra, Umbra. To activate this option click on the data tab at the bottom 
> of the satellite listing. 
> The simulation mode offers a variety of time steps down to 0.25 seconds.
> Selecting the ISS and stepping through an eclipsed part of the orbit tonight I 
> estimated that it took the ISS 8.75 seconds to cross the Penumbra.
> If 7km per second is about right for the ISS then the Penumbra is 59.5 
> kilometres wide +/- about 1.75km.
> My workings may well be adrift but you get the idea.
> What an interesting utility, for us telemetry nuts it will add an extra 
> dimension to solar panel data.
> Off to try it on some higher flying birds.
> 73 All  G7HIA
> Happy Weekend
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