Some Terms You Should Know: 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.