From the July 2011 issue

I am perplexed by sidereal time; would you go over this concept?

Jim Cox, Victoria, British Columbia, Canada
By | Published: July 25, 2011
Sidereal time (left) is measured with respect to background stars while solar time references the Sun. Earth needs to rotate nearly an extra degree for the Sun to pass the reference point; this accounts for almost 4 more minutes in a solar day than a sidereal day. Astronomy: Roen Kelly

Sidereal time literally means “time by the stars.” A sidereal day is a measurement of one rotation of Earth referenced to distant background stars — think of this as the amount of time it takes a particular star to come back to the same place in our sky the next night.