In order to describe the orientation of a galaxy, we can refer to its position angle. This angle is set up by drawing a line north from the center of the galaxy and a second line through the major ("long") axis of the galaxy. Position angles are measured from north toward the east (counterclockwise) as viewed in the sky. In the following illustration, the galaxy has a position angle of 120^o. Note this is not a measure of how the galaxy is tilted to our line of sight (whether it appears oblique, face-on, etc.)

The orientation of double star systems is also described using position angles. In this case, a line is drawn north from the major (brightest) component star and the other line is drawn from the major to the minor star. Accurate measurement of the PA of a double star is an important component because over time it can tell us how the stars are moving with respect to each other.

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This page last updated on December 31, 1999