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MPO Canopus – Astrometry
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 |
Criteria |
|
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. |
