# Calculating magnitudes - was [Re: Binoculars & Mag]

Philip Chien (kc4yer@amsat.org)
Wed, 14 Oct 1998 17:05:02 -0400

```Bjoern Gimle <b_gimle@usa.net> wrote-

>For the 8x56, an old person uses only 8x4 or 8x5 mm = 32-40 mm
>instead of 56 mm. In the case of 7x18, all healthy persons would
>utilize the full 18 mm.
>
>For 8x56, 4.2 + 5 * log( 8) is 8.7
>For 7x18, 4.2 + 5*log(18/5) is 7.0 and 4.2+5*log(18/7) is 6.3

Is there a reasonably accurate formula for calculating the predicted
magnitude for a satellite?  I suspect that it would have to include the
satellite's cross section area, albedo, percentage sunlit (usually either 1
or 0), and distance from observer.  I would suspect that the same formula
could be used to calculate the magnitude of the moon, planets, and any
other objects which shine by reflected sunlight.

I have the graphs from the Desmond Hele book but would like a formula which
I can plug in to a spreadsheet.

Philip Chien, KC4YER
Earth News
world (in)famous writer, science fiction fan, ham radio operator,
all-around nice guy, etc.
```