Re: Report on eclipsed satellites Oct. 3

From: Daniel Deak (dan.deak@sympatico.ca)
Date: Tue Oct 04 2005 - 00:24:11 EDT

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    Daniel Deak wrote:
    
    
    > I recorded my comments and will make a more detailed report tonight 
    > (Eastern time) as I now have to go to work.
    
    
    So here it is !
    
    I had prepared observations for 6 satellites that looked interesting according 
    to Russell and Bjorn. I used Skymap intensively for the first time and was able 
    to display trajectories with the color code for the portions of orbits in lunar 
    shadow. So I used fresh elsets and ran my own predictions for objects number :
    22220 23561 24298 22566 15944 13367 (in chronological order of appearance).
    
    Of those six, objects 23561 and 22566 were missed because of set-up time and 
    inability to find the objects soon enough.
    
    Here are the results of my magnitude estimates for the four objects seen along 
    with notes on the trajectory :
    (mag accuracy  0.8    time accuracy  2 s   times in UTC)
    
    object 22220  SL-16 R/B
    observed from 8:11:06 to 8:16:20
    8:11:24  mag 6.5 and increasing
    8:12:35  mag 5
    8:13:12  mag 4.5
    8:13:18  culmination
    8:13:40  mag 4.5
    8:14:14  mag begins to drop
    8:14:15  approximate middle of shadow
    8:14:33  mag 7.5
    8:14:42  mag 8.3
    8:14:58  mag increases again
    8:15:39  mag 7
    8:16:02  mag 7
    
    object 24298  SL-16 R/B
    observed from 8:21:15 to 8:27:10
    8:21:15  mag 7
    8:22:10  mag 6.5
    8:22:30  mag 6.5
    8:22:45  slowly fades
    8:23:37  mag 7
    8:23:42  culmination
    8:24:08  mag 7.5
    8:24:15  approximate middle of shadow
    8:24:52  mag 7.5
    8:25:29  mag 7
    8:26:26  mag 7
    8:27:03  mag 7.5
    
    object 15944  Cosmos 1674
    observed from 8:35:48 to 8:39:32
    8:36:02  mag 7
    8:36:32  mag 7.3
    8:36:52  culmination
    8:37:15  approximate middle of shadow
    8:37:30  mag 7.5
    8:38:11  mag 8
    8:38:44  mag 8.3
    8:39:25  mag 8.5
    
    object 13367  Landsat 4
    observed from 8:42:52 to 8:47:27
    8:43:51  mag 6  (already in Moon shadow)
    8:44:19  mag 6
    8:44:20  approximate middle of shadow
    8:44:26  culmination
    8:44:39  mag 6
    8:45:06  mag 6
    8:45:10  small decrease in mag
    8:45:42  mag 6.5
    8:46:25  mag 7.3
    8:47:05  mag 7.7
    
    ANALYSIS  (for what it's worth...)
    
    The best effect of an eclipse was seen with #24298 where the lowest magnitude of 
    the high portion of the pass was recorded at the center of the predicted shadow.
    
    Object 22220 was once a flasher (see PPAS database) that has slowed to become 
    quite stable. I think the magnitude variation is a combination of a very slow 
    tumble and the lunar shadow.
    
    Object 13367 gave me high expectations because the shadow was centered on the 
    trajectory, with maximum shadow at or near culmination. It proved disappointing. 
    The effect of the shadow was nearly unnoticeable.
    
    Object 15944 was supposed to disappear from view, according to Skymap, but 
    remained visible, although faint on the last part of the obs. Its magnitude was 
    always near the value predicted with SatSpy.
    
    CONCLUSION
    
    I guess the phenomenon witnessed on Earth during annular or partial eclipses of 
    the Sun is also true for satellites, I mean that during a partial eclipse, we 
    don't really notice a drop in sunlight intensity until the Sun is almost 
    entirely hidden by the Moon. Enough light still reaches the satellites to make 
    them almost as easy to observe as without shadow effect. My observed drop in 
    magnitude in nearer 1 or 2 than 4 or 5, so one has to be careful to be able to 
    really observe a difference in magnitude due to lunar shadow compared to a 
    regular pass.
    
    I haven't made positional obs for some time because of my occupations but I 
    enjoyed doing this hour of observation early this morning with such a nice sky.
    
    Dan
    
    -- 
    Daniel Deak
    Webmestre, site Obsat
    L'Avenir, Quebec
    
    COSPAR site 1747 : 45.7275N, 72.3526W, 191 m., UTC-4:00
    
    Site en francais sur les satellites:
    French-language satellite web site : http://www.obsat.com
    
    
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