Re: Satellite Elements from Astrometric Observation.

From: Greg Roberts (
Date: Wed Mar 25 2009 - 10:17:12 UTC

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    Afternoon John
    Im sending you by seperate mail a picture taken with an alt/az mount tracking as 
    an equatorial mount that will work - Ive already done an astrometric solution on 
    it with several astrometric programs so Ive given you all the relevant details 
    with the jpg image sent to you.
    It is a bit unfortunate that the astrometric programs currently "readily" 
    available cannot handle trailed stars as there are many instances where stars 
    are trailed- eg tracking on an asteroid or comet which do not move at sidereal 
    rate. One would have thought that after all these years such software would 
    exist. I am aware of one program but it is not easily available - Im trying to 
    get a copy of it at the moment.
    Unfortunately many of the video images will be time stamped and will cause the 
    problem you had with Derek's image. This area of the frame will have to be 
    blocked out in some way so the astrometric program does not see it - another 
    problem is that I dont think everyone is using the same time stamp program which 
    means there is no universal "block out' for all programs.
    I did try an idea I had late or rather early one morning. Take an image that has 
    trailed stars and measure the X,Y coords of the satellite image and 3-8 bright 
    stars trails - the end depending on whether the time of the image is start or 
    end of frame.
    Then convert these X,Y readings to fit on (say ) a 640 x 480 grid.(Since not 
    everyone has the same size image in terms of pixels along X,Y axis).
    Somehow or other plot these points on such a grid so you then have an image 
    showing the location of the satellite and the 3-8 brightest stars appearing as 
    dots. Maybe one could also measure the intensity of the pixels when determining 
    the X,Y coords and plot the dots with a size depending on intensity.
    Now take this plotted image and put it in an astrometric program - I like PIXY 
    because its freeware and do an astrometric solution. The 3-8 bright stars should 
    enable a plate solution to be obtained and you can get the position of the 
    In other words we are "converting the trailed images into point sources".
    I tried this in a BASIC program but couldnt solve the problem of how to save the 
    screen display in BASIC as a file- BMP or PNG -- maybe someone reading this will 
    be able to ?
    Maybe this will work or maybe it wont -- I dont know how the astrometric 
    programs will respond to "seeing" this as a photograph?
    Just an idea..
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