Web camera can be successfully used for measuring of position angle of double stars. Position angle is measured in counter clockwise direction from the north direction. For measuring distances and angles in bitmaps is sufficient a simple math (Pythagoras's theorem and goniometrics functions). The only thing we must do is to find out the north direction. It is very simple task for web cams - it is enough to watch the star's movement caused by rotation of the Earth (if an observer has mount with drives, the drives must be off). The stars move from the east to the west. South-north direction is perpendicular to east-west direction.

Here are some of my photographs of star trails:

Castor A, B	Gamma Delphini	Epsilon 1, 2 Lyrae

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Last Update: 15.5.2001