Re: Rosetta Obs

From: Bill Dillon (dillon1@houston.oilfield.slb.com)
Date: Thu Mar 03 2005 - 10:28:58 EST

  • Next message: Greg Roberts: "Obs 01 March 2005 Part 2"

    Ted,
    
    Are your magnitude estimates based only on the small box-like body?  I 
    would think the 32 m solar array would contribute a fair amount of light 
    in its own right, even without a specular reflection.
    
    I suspect that the phase angle will be much larger during the close 
    fly-by, with the solar arrays more edge-on, in which case your formula 
    could be more in line with observations.
    
    Regards,
    
    --Bill Dillon
    
    
    Ted Molczan wrote:
    > Joseph A. Dellinger posted obs by Bill Dillon at the George Observatory near
    > Houston, Texas:
    > 
    > Rosetta       C2005 03 01.18294 11 06 40.09 +02 24 00.0          17.0 R      735
    > Rosetta       C2005 03 01.19055 11 06 37.60 +02 24 03.7          17.0 R      735
    > Rosetta       C2005 03 01.19689 11 06 35.47 +02 24 06.6          17.0 R      735
    > 
    > 
    >>the mags are really "unfiltered", but "R" is a good approximation.
    > 
    > 
    > Mag 17 is very bright for the range, about 0.0089 A.U. (1.33 million km). See
    > appended ephemeris. My formula predicts mag 21. Had the object been only 1000 km
    > away, it would have been mag 1.4, unlikely for Rosetta's non-specular, 2.8 x 2.1
    > x 2.0 m box-like body.
    > 
    > Rosetta's low phase angle, 6.8 deg (see S-T-O column in ephemeris), meant that
    > the observer was almost directly between it and the Sun. Since its large solar
    > array (32 m span) is aimed at the Sun, it seems likely to have been flaring,
    > i.e. sending a bright specular reflection toward the observer. Imagine an
    > observer on Earth between the Sun and Rosetta in this artist's conception:
    > 
    > http://satobs.org/seesat_ref/Rosetta/Rosetta.jpg
    > 
    > The unusually bright obs at Czechia, some 22 h later, was made under similar
    > conditions, with phase angle near 5.8 deg:
    > 
    > http://satobs.org/seesat/Mar-2005/0022.html
    > 
    > Ted Molczan
    > 
    > 
    >       Target Body: Rosetta (Spacecraft)
    > Observer Location: Houston, TX
    >       Coordinates: 9521'37.1''W, 2945'25.9''N
    > 
    >   From: A.D. 2005-03-01 04:23 UT
    >     To: A.D. 2005-03-01 04:44   
    >                         
    > *******************************************************************************
    >  Date__(UT)__HR:MN     R.A._(ICRF/J2000.0)_DEC         delta    deldot    S-T-O
    > *******************************************************************************
    >  2005-Mar-01 04:23     11 06 39.86 +02 23 54.2  0.0089222014  -4.19264   6.8419
    >  2005-Mar-01 04:24     11 06 39.64 +02 23 54.6  0.0089205194  -4.19124   6.8406
    >  2005-Mar-01 04:25     11 06 39.42 +02 23 54.9  0.0089188379  -4.18984   6.8393
    >  2005-Mar-01 04:26     11 06 39.19 +02 23 55.2  0.0089171571  -4.18843   6.8380
    >  2005-Mar-01 04:27     11 06 38.97 +02 23 55.5  0.0089154768  -4.18702   6.8367
    >  2005-Mar-01 04:28     11 06 38.74 +02 23 55.9  0.0089137970  -4.18560   6.8354
    >  2005-Mar-01 04:29     11 06 38.51 +02 23 56.2  0.0089121179  -4.18418   6.8341
    >  2005-Mar-01 04:30     11 06 38.29 +02 23 56.5  0.0089104393  -4.18275   6.8328
    >  2005-Mar-01 04:31     11 06 38.06 +02 23 56.9  0.0089087613  -4.18132   6.8315
    >  2005-Mar-01 04:32     11 06 37.83 +02 23 57.2  0.0089070838  -4.17988   6.8302
    >  2005-Mar-01 04:33     11 06 37.60 +02 23 57.5  0.0089054070  -4.17844   6.8289
    >  2005-Mar-01 04:34     11 06 37.37 +02 23 57.8  0.0089037307  -4.17700   6.8276
    >  2005-Mar-01 04:35     11 06 37.14 +02 23 58.2  0.0089020550  -4.17555   6.8263
    >  2005-Mar-01 04:36     11 06 36.90 +02 23 58.5  0.0089003799  -4.17410   6.8250
    >  2005-Mar-01 04:37     11 06 36.67 +02 23 58.8  0.0088987054  -4.17264   6.8237
    >  2005-Mar-01 04:38     11 06 36.44 +02 23 59.1  0.0088970314  -4.17118   6.8224
    >  2005-Mar-01 04:39     11 06 36.20 +02 23 59.5  0.0088953581  -4.16971   6.8211
    >  2005-Mar-01 04:40     11 06 35.97 +02 23 59.8  0.0088936853  -4.16824   6.8198
    >  2005-Mar-01 04:41     11 06 35.73 +02 24 00.1  0.0088920132  -4.16676   6.8184
    >  2005-Mar-01 04:42     11 06 35.50 +02 24 00.4  0.0088903416  -4.16529   6.8171
    >  2005-Mar-01 04:43     11 06 35.26 +02 24 00.7  0.0088886707  -4.16380   6.8158
    >  2005-Mar-01 04:44     11 06 35.02 +02 24 01.1  0.0088870003  -4.16232   6.8145
    > 
    > 
    > 
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    -- 
    __________________________________________________________________
    
    Bill Dillon               Note that my email address has changed:
    Schlumberger-SIS          dillon1@houston.oilfield.slb.com
    (713) 513-2162
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