Re: Bright Sat Photometry?

From: George Roberts (
Date: Tue Sep 15 2009 - 04:29:07 UTC

  • Next message: Scott: "Satobs 15 Sept 2009"

    Did you get marco's reply?  He said to try maxim DL.  You can set up a line in 
    the software along the trail and it graphs the change in brightness.  Marco did 
    lots of stuff with this to get light curves of tumbling satellites from multiple 
    observations.  Check it out on his website.
    Estimating a satellite's brightness is much easier with binoculars and a little 
    experience.  A movie camera works well also.  A long exposure doesn't work so 
    well.  I don't know of any software that will add up all the brightness in the 
    line.  Especially since the star dots are often saturated.  It's better to 
    compare a point source to other known brightness stars.  Pretty much all 
    non-variable stars you are likely to see/image have a known brightness.
    Also be aware that a satellite's brightness changes significantly depending on 
    the sun-sat-observer angle.  So its brightness at one part of the trail may by 
    twice as bright as its brightness 10 degrees later.  Or 1000 times as bright 
    - George Roberts
    ----- Original Message ----- 
    From: "npr61" <>
    To: "Gerhard Groenewald" <>; <>
    Sent: Monday, September 14, 2009 7:01 PM
    Subject: Re: Bright Sat Photometry?
    > Mr. Groenewald:
    > I'm wondering if I can use a DSLR to take raw images and do comparative 
    > brightness (Sat vs. ref star).  With only a 50mm lens & short exposures, 
    > bright stars should remain point-like and thus amenable to measurement with an 
    > aperture.  The short sat trail, entirely within the frame, would require a 
    > rectangle to encompass it.  I imagine it will be tough to avoid saturation, 
    > and may not give useful results at all.  I basically wondering if it is 
    > possible to "measure a streak".  The goal is not research grade work, just fun 
    > with a camera and software.
    > Forgive my ignorance, but I figured this would be the place to ask about 
    > measuring sat brightness.  All of the AAVSO info I've read does not really 
    > address sats.
    > Neal Robichaux
    > 29.9884N
    > 92.1498W
    > ----- Original Message ----- 
    > From: "Gerhard Groenewald" <>
    > To: "'npr61'" <>
    > Sent: Sunday, September 13, 2009 10:11 AM
    > Subject: RE: Bright Sat Photometry?
    >>I am not exactly sure what it is that you wish to do.
    >> However I am using a Canon 20d with various lenses.
    >> You may use my images at
    >> They are all reworked images and if you wish to get unedited copies, please
    >> contact me.
    >> Regards
    >> Gerhard Groenewald
    >> RSA
    >> -----Original Message-----
    >> From: npr61 []
    >> Sent: Sunday, September 13, 2009 1:18 AM
    >> To:
    >> Subject: Bright Sat Photometry?
    >> Hello:
    >> Are there available software that could be used for comparative
    >> photometry of a bright sat, i.e. ISS, trail?  Have been toying with the
    >> idea of buying a used Digital Rebel, fitting it with a 50mm f/1.8 lens,
    >> and then taking short, say 8-12 second unguided exposures of the ISS
    >> against brighter background stars.  Ideally, it would be nice to be able
    >> to create a rectangular aperture over all or a portion of the ISS trail,
    >> with circular apertures for the ref/check stars.
    >> I've no background in this subject other than a lot of reading over the
    >> last few months. The goal would be a simple and fun way to put
    >> brightness numbers on a given pass, to perhaps the accuracy of that of a
    >> good visual observer.  Am very much considering AIP4WIN for general
    >> knowledge, but don't think that it could perform the task.  On the other
    >> hand, wrestling with something like IRAF would perhaps defeat the "fun"
    >> intent.
    >> Any advice would be welcome.
    >> Thanks,
    >> Neal Robichaux
    >> 29.9884N
    >> 92.1498W
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