Most clocks keep "solar time". A solar day is one in which the earth makes one rotation and the sun returns to the same place in the sky. Once you have a SIDEREAL CLOCK on your wall, if you see that it's 5:55 local sidereal time, you know that Betelgeuse and Orion are on the meridian. If it's 18:37 sidereal time, Vega and the constellation Lyra are on the meridian.
