Some Terms You Should Know: Double Stars

These are some terms you will come across in your lab class dealing with double stars.
Barycenter
The center point of a binary system that both stars rotate about.  A line through the center of both stars will always pass through the barycenter.
Binary Star or Binary System
A pair of stars that orbit each other about a common center.
Plate Scale
A conversion factor, for a specific photograph, of linear distance to angular distance. (E.g., from mm to seconds of arc.)
Position Angle
In a binary system, the counter-clockwise angle between a line due north from the larger star and a line between the two stars.
Separation
Here, the angular distance between two stars in a binary system as seen from Earth.  (This may change depending on the time of observation.)

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 This page was last updated on 6 April 1998
and is © 1998 by Jim McDonald.