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

John Heath g7hia at btinternet.com
Fri Sep 30 15:17:08 PDT 2011

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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