clock star

clock star

A bright star, usually situated near the celestial equator, whose position and proper motion are very accurately known so that it can be used for the exact determination of time, for the determination of the error of observatory clocks, and for correction of the positional observations of other stars.

clock star

[′kläk ‚stär] (astronomy) Any star that is used to measure time; always a bright star, whose right ascension is well known.