# RE: Satellite Magnitude Calculation

From: David Tiller (dtiller@captechconsulting.com)
Date: Mon Oct 17 2011 - 16:18:58 UTC

• Next message: George Roberts: "Re: Satellite Magnitude Calculation"

```Steve,

One person to ask is Chris Peat (a regular on this list). He maintains the most excellent website heavens-above.com from which the following FAQ answer was copied:

http://heavens-above.com/ShowFAQ.aspx?FAQID=515

The brightness of a spacecraft is influenced by several factors, including its size, orientation, reflectivity of its surfaces, distance from the observer, and the angle between the sun, spacecraft and observer. The size and reflectivity determine the "intrinsic" brightness, and this is either estimated from observations or from a knowledge of the size and type of coverings used in the construction. The distance, and sun-satellite-observer angle can all be calculated from the orbit. This leaves just the orientation or attitude, which is usually unknown, and often varying rapidly (e.g. a tumbling rocket body). For this reason, our magnitude estimates should only be treated as a rough guide, and the actual brightness you see could be considerably more or less than this.

He may be willing to give you a peek into his algorithm.

--
David Tiller
(804) 304-0638 | dtiller@captechconsulting.com

________________________________________
From: seesat-l-bounces+dtiller=captechconsulting.com@satobs.org [seesat-l-bounces+dtiller=captechconsulting.com@satobs.org] on behalf of Steve Daniels [steve@daniels270.eclipse.co.uk]
Sent: Monday, October 17, 2011 12:13 PM
To: seesat-l@satobs.org
Subject: Satellite Magnitude Calculation

Hi All
A programmer I know is writing software mainly for amateur radio use, but he
is including satellite tracking, I have managed to persuade him to include
satellite visibility from a visual point of view.
I wonder if someone would be kind enough to tell me how to calculate the
magnitude of brightness of the satellite? I can see this comes from the RCS
value but don't know how.
And is there is a good formula for calculating satellite visibility

Thank you

Steve Daniels
G6UIM

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