A star clock is a method of using the stars to determine the time. Some methods require no tools; others use an astrolabe and a planisphere.

A clock's regulator can be adjusted so that it keeps the Mean Sidereal Time rate. When it is then set to an observer's Local Mean Sidereal Time then a star will transit the meridian (passing directly north or south) at the sidereal time of the star's Right Ascension.

[edit] See also

• Sidereal time

[edit] External links

• Telling Time by Sun and Stars by John P. Pratt
• Inquiry.net

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