# [amsat-bb] Re: calculation of eclipse

Ken Ernandes n2wwd at mindspring.com
Thu Sep 29 17:18:28 PDT 2011

```Unfortunately it's not a simple formula, but rather a process.  To compute, you need to not only propagate the satellite orbit (as is done in a tracking program), but also need an algorithm to generate positions of the Sun relative to the Earth.  (The latter is available in a book called "Astronomical Algorithms" by Jean Meeus.)  You will also need to consider the diameter of both the Sun and the Earth.

The eclipse geometry is explained in the book "Satellite Orbits" by Montenbruck and Gill.  From there you need to develop a sampling method to determine entry and exit times.

Bear in mind that the eclipse geometry and timing is different on a case-by-case basis with the exception of some specialized orbits (which ARISSsat is not in).

I'm sorry I couldn't offer a more satisfying answer.

73, Ken N2WWD

On Sep 29, 2011, at 7:33 PM, <normn3ykf at stny.rr.com> wrote:

> Hi all!!
> How does one calculate the period and time of entry and exit of eclipse?
> I'm going to be helping a friend do an Arissat presentation for her class. Due to the fact of the battery failing, this gives a 15 minute hold before the power management allows transmission. So, for any chance of receiving the bird, it has to  be in sunlight for 15 minutes (or so).
> I'd prefer a mathematical formula. Echo goes through some of the same trials.
> Thanks,
> Norm
> BTW: I am an engineering student, just throw the math my way.
>
>
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