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Thread: MPCORB Problem

  1. #1
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    Default MPCORB Problem

    Bob,

    Is there any chance that you made changes to the MPCORB database or the calculations that take it for use it in ACP?

    I cannot center asteroids anymore. When I type "MP Concordia" into the SingleImage web form and get coordinates, the values in the RA Dec boxes say "emphemeris." And that's right. However, the computed coordinates as posted in the log are off in RA by about 8 or 9 arcminutes (34 seconds of time) to the west. There's a very small error in declination, a couple arcsec, as well. This puts the target outside of my smallish FOV. The image is centered at the requested, incorrect coordinates.

    When I put an NGC object in the Target Name window and get coordinates, and then take an image, the target is dead center, and not displaced in any direction. NGC uses a different database.

    I had the same result when I tried to image MP Europa (the minor planet) - the telescope pointed too far to the west nominally by the same 8-9 arcminutes.

    I don't recall this being a problem in the past, though it's been a long time since I've visited asteroids. I wonder if others have noticed this.

    EDIT: Just another point about the data.

    Starry Night Pro shows the asteroids as well. I could see there the FOV I actually captured, which was west of the asteroid's real position, and when I manually moved the telescope to the position described by SNP, Concordia and Europa were imaged in their correct position against the correct FOV.
    Last edited by Dick Berg; Jan 16, 2010 at 12:31. Reason: added more information
    Dick
    www.VirgilObservatory.us
    Pier-mounted Meade 12-inch SCT "classic"
    Optec TCF-S focuser
    SBIG CFW-8A and ST7-XMEv
    H-alpha, BVRI, RGB & Clear filters
    FOV ~15’ x 10’



  2. #2
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    Default

    I haven't changed the MPCORB database... that's a product of the Minor Planet Center. And the making of the mdb file just uses the same orbital elements as are in the text file from MPC.

    The MPCORB component was changed 30-Sep-09 for 32-and 64-bit compatibility. It simply supplies orbital elements to AcquireSupport.CalcEphemeris(). That, in turn, uses the Kepler and NOVAS components to get the final J2000 coordinates. Both Kepler and NOVAS are now the responsibility of the ASCOM platform development team, specifically Peter Simpson. If you installed ASCOM 5.5 I think you have the latest ones. I don't believe he changed anything in the algorithms or the object model, he just made them more friendly to .NET, Win7/Vista, 64 bit, etc.

    I just got in from NM, so I'm not in a position to construct a test harness, contact Peter regarding possible changes, etc. If you want, I'll lend a hand next week though.
    -- Bob

  3. #3
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    Default

    I don't know what could have changed. I will do some more asteroid imaging next clear night, although I expect to see the same problem. I recall now that a couple weeks ago I captured a couple hundred short duration images of Persephone but they were all at the wrong field of view.

    Maybe a few others with a poor night at hand could try a few minor planet single images and report back what happens. If it matters, I was just using the Single Image web form and only typing in "MP <asteroid name>" - it was not a plan with "MP <asteroid name>" in it.

    Thanks for thinking about this.
    Dick
    www.VirgilObservatory.us
    Pier-mounted Meade 12-inch SCT "classic"
    Optec TCF-S focuser
    SBIG CFW-8A and ST7-XMEv
    H-alpha, BVRI, RGB & Clear filters
    FOV ~15’ x 10’



  4. #4
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    Quote Originally Posted by Bob Denny View Post
    I haven't changed the MPCORB database...
    But you do recall that there was an error a while back with the epoch year calculation of the database, and that was found by Charles Lemaire in November 2008. (http://forums.dc3.com/showthread.php...CORB#post19729)

    In April 2009, Don Pray had very elusive issues as well that were fixed using the corrected MPCORB. (http://forums.dc3.com/showthread.php...CORB#post18952)


    Is there some chance that the old, incorrect MPCORB got reissued in a recent hot fix? The files all get loaded into the .../Common/ASCOM/ directory. I'm going to check mine again.
    Dick
    www.VirgilObservatory.us
    Pier-mounted Meade 12-inch SCT "classic"
    Optec TCF-S focuser
    SBIG CFW-8A and ST7-XMEv
    H-alpha, BVRI, RGB & Clear filters
    FOV ~15’ x 10’



  5. #5
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    Dick: just to keep you imaging while the MPCORB is sorted out: using 1-line MPC orbital format in an ACP plan (HF 10) still gives well-centered MP images.
    measuring space rock rotation rates, live from Albuquerque NM

  6. #6
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    Thanks, Eric.

    I didn't think about what the problem might be the other week, when I took the long series of images. That night, there were two asteroids in the same FOV, and I thought it would be fun to image them crossing/moving through the field, for a couple of hours. Of course, nothing was there, and I was surprised about that at the time, but I didn't think more about it.

    At least I can stack all these images to get a REALLY DEEP image of that region of the sky, even though there's nothing interesting there!
    Dick
    www.VirgilObservatory.us
    Pier-mounted Meade 12-inch SCT "classic"
    Optec TCF-S focuser
    SBIG CFW-8A and ST7-XMEv
    H-alpha, BVRI, RGB & Clear filters
    FOV ~15’ x 10’



  7. #7
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    Yes, I do recall. I looked at the MPCORB.wsc file for changes yesterday, but didn't look at the maker MakeDB.wsf. I corrected MakeDB back in Nov 2008 for the Lemaire reported problem and re-posted the update to the ASCOM download area. You can see my edit tracks in MakeDB.wsf.

    So if you are using the current MPCORB, which has the fix, the epoch shouldn't be an issue.

    I don't include MPCORB or any of the other ASCOM widgets (Kepler, NOVAS, MiniSAC) in ACP Hotfixes. I do include them in the full ACP install. Did you maybe re-run the ACP installer?
    -- Bob

  8. #8
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    Default My Bad

    Well, I come to discover that the MPCORB.dat file on the observatory computer was dated January 2008 - pre-error-fix! In sorting through the April 2009 problem Don was having, I did remake my copy for simulation on my in-house computer, but I never copied that file out to the observatory.

    I know this won't be a problem for me from now on. Case closed.

    Just for fun I've attached an image showing the two FOVs mosaicked - on the right the predicted position of Concordia and on the left the actual position. North is up and East to the left.
    Attached Images Attached Images
    Last edited by Dick Berg; Jan 16, 2010 at 17:01. Reason: added a picture
    Dick
    www.VirgilObservatory.us
    Pier-mounted Meade 12-inch SCT "classic"
    Optec TCF-S focuser
    SBIG CFW-8A and ST7-XMEv
    H-alpha, BVRI, RGB & Clear filters
    FOV ~15’ x 10’



 

 

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