How can I avoid common mistakes while doing astrometry?

This item is based on an exchange of E-mail messages on the Minor Planet Mailing List

Tim Spahr put together a list of the most common mistakes he finds in astrometric material submitted to the Minor Planet Center:

• http://cfa-www.harvard.edu/~tspahr/astrom.howto
• a local copy of Tim's HOWTO

Bill Gray provided a very useful check to verify that one's time is accurate:

May I suggest that one way of checking this is to observe a really fast moving artificial satellite, such as 1969-046F. If your timing isn't right, it will be apparent right away (poor match between your observations and the ephemerides.) And if your timing _is_ right, we can use your data to polish up future ephemerides.

You can get ephemerides for some of these objects from the MPC's Earth-Orbiting Space "Junk" Page,

• http://cfa-www.harvard.edu/iau/SpaceJunk/SpaceJunk.html

and some more info about them at

• http://home.gwi.net/~pluto/mpecs/pseudo.htm#artificial

IMP-8 consistently moves at a bit over an arcsecond per second, so it makes an excellent check. ACE, Wind, and Geotail may also be useful at parts of their orbits. SIRTF is now too far away to be visible, and SOHO has always been too close to the sun (at the inner Lagrangian point) to really be visible. WMAP is nicely placed near opposition, but doesn't move very briskly (under an arcsecond a minute).

Also, you can get ephemerides for CXO (Chandra X-Ray Observatory) and INTEGRAL from JPL's Horizons:

• http://ssd.jpl.nasa.gov/cgi-bin/eph

Both might make good "practice" targets. If you get astrometry for these or other artificial satellites, please send it to MPC and to astrometry_distro@yahoogroups.com .