MadSci Network: Astronomy

Re: What is meant in the star tables by negative parallaxes?

Date: Fri Aug 17 13:58:08 2001
Posted By: Donald Terndrup, Faculty, Astronomy, Ohio State University
Area of science: Astronomy
ID: 997983027.As

Hi --

I'd have to see an example of your chart to see what data are being shown, in
case the chart actually plots something like stellar magnitudes and calls it

In any case, parallaxes are always positive quantities as you correctly
pointed out. But as with any quantity, there are errors of measurement.  When 
stars are farther off than 50 - 100 pc, the parallax is nearly zero, and an 
error of measurement can place the actual value slightly less than zero.

If your chart grabbed parallaxes from a catalog without paying attention to
what the errors are, it is entirely possible that there would be negative
parallaxes shown.

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