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The Minor Planet Observer
Palmer Divide Observatory

2007 Shoemaker Grant Recipient

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MPO Canopus – Astrometry

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Up to 75 reference stars can be used to find the "plate constants" for the image. The Reductions page shows the residuals for each star, with color coding to identify "offending" stars quickly. Also shown are the standard deviations when back-computing the positions of the reference stars. This serves as one gauge for the accuracy of the derived position for the asteroid (but not the only gauge). Canopus initially removes stars with excessive residuals but you can override the process to include or exclude individual
stars as you see fit.

The MPC button at lower right generates an MPC compatible report from the saved reductions files. When the new 132 character/line format is adopted, a simple change in the configuration settings will switch Canopus over to the new format.

Overriding the Astrometry Solution

You can change which stars are included in the astrometric solution. Each time you add or remove a star from the solution, Canopus automatically re-computes the residuals and standard deviations based on the new astrometric solution.

Color Coding

To make reductions go faster, the RA and Dec residual columns in the Data Table are color-coded.

Color Status


White Good Both the RA and Dec residuals are < 0.25 arcseconds
Silver Not Used The star has been eliminated from the calculations. Both residuals are set to 99
Yellow Active Row The active (current) row if the status is Good or Not Used. If the status is Fair, Poor, or Bad, the row keeps its status color, even when active
Green Fair The RA, Dec, or both residuals are in the range of 0.25-0.39 arcseconds
Blue Poor The RA, Dec, or both residuals are in the range of 0.39-0.74 arcseconds
Red Bad The RA, Dec, or both residuals are 0.75 arcseconds or greater

Text is black when the line is white, yellow, or silver. If the line is red, green, or blue, the text is white when the row is not the active row. If a red, green, or blue line is the active row, the text changes to bold and yellow.

If a large number of stars are blue and red, it could be that you misidentified one or both stars in the two-star alignment process or that one or both have bad catalog positions. Try re-matching the chart to the image. If the result of auto-matching and nothing you do with the Configuration settings improves the situation, try manually aligning the chart and, if absolutely necessary, using the full manual method.


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This page was last updated on 01/19/11 05:14 -0700.
All contents copyright (c) 2005-2011, Brian D. Warner
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