Re: Rosetta fly by: about magnitudes

From: Bram Dorreman (bram.dorreman@skynet.be)
Date: Wed Mar 02 2005 - 17:45:28 EST

  • Next message: Kevin Fetter: "article on spaceflight now about space track policy"

    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?
    
    Ted Molczan replied:
    
    > 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"
    
    Thanks Ted and other repliers too.
    Before I received these replies I recalculated my topocentric predictions so
    that distance unit is km. What would be the formula when "delta" unit is km?
    
    Meanwhile I can start with the original output in which "delta" is in AU.
    
    ESA's statement that Rosetta would be mag +8 or +9 at 10000 km range makes
    it mag +3 or +4 at 1000 km (100 times as bright -> mag 5 difference). I now
    know what standard magnitude range I can apply in my further calculations.
    
    It may all be in vain because we now have a real winterperiode with clouded
    skies, snow and temperatures below zero (Celsius) during the whole days.
    This will cause we cannot "hunt happily".
    
    Best regards..Bram Dorreman
    
    
    
    
    -------------------------------------------------------------------------
    Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive:  
    http://www.satobs.org/seesat/seesatindex.html
    



    This archive was generated by hypermail 2b29 : Wed Mar 02 2005 - 18:02:11 EST