Bram Dorreman wrote:
> Who can tell me the formula to calculate the stellar
> magnitude from a self defined absolute magnitude (phase 90°
> and distance 1000 km), range and sun-target-observer angle?
>
> Another question: what might be a reasonable value for
> Rosetta's standard magnitude?
I have derived the following formula, for use with data provided by the
ephemeris:
mag = 32.17 + 5 * log10("delta") + 0.01 * ("S-T-O" - 90), +/- 2
where: "delta" = Target apparent range relative to observer. Units: AU
"S-T-O" = Sun-Target-Observer angle; target's apparent PHASE ANGLE as
seen at observer's location at print time. Units: DEGREES
The above formula is based on my estimated standard magnitude of 6.3 +/- 2 mag
(1000 km, phase angle 90 deg), based upon the ESA's description: "a large
aluminium box with dimensions 2.8 x 2.1 x 2.0 metres"
http://esamultimedia.esa.int/docs/science/media/rosetta2004.pdf
For example, here is the relevant Horizon's output for 2005 Mar 04 21:49 UTC,
for Bram's site coordinates:
"delta" = 0.0000534570 A.U.
"S-T-O" = 88.0465 deg
Using my formula, I estimate mag = +10.8 +/- 2, in rough agreement with ESA's
estimate of about mag +8 or +9:
http://www.esa.int/esaCP/SEMMTBYEM4E_index_0.html
Ted Molczan
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