Editing Sidereal time (section)

==Comparison to solar time==
[[File:Sidereal time.svg|thumb|upright=1.25|Sidereal time vs solar time. '''Above left''': a distant star (the small orange star) and the Sun are at [[culmination]], on the local meridian '''m'''. ''Centre'': only the distant star is at culmination (a mean [[sidereal day]]). ''Right'': a few minutes later the Sun is on the local meridian again. A [[solar day]] is complete.]]

[[Solar time]] is measured by the apparent [[diurnal motion]] of the Sun. Local noon in apparent solar time is the moment when the Sun is exactly due south or north (depending on the observer's latitude and the season). A mean solar day (what we normally measure as a "day") is the average time between local solar noons ("average" since this varies slightly over a year).

Earth makes one rotation around its axis each sidereal day; during that time it moves a short distance (about 1°) along its orbit around the Sun. So after a sidereal day has passed, Earth still needs to rotate slightly more before the Sun reaches local noon according to solar time. A mean solar day is, therefore, nearly 4 minutes longer than a sidereal day.

The stars are so far away that Earth's movement along its orbit makes nearly no difference to their apparent direction (except for the nearest stars if measured with extreme accuracy; see [[parallax]]), and so they return to their highest point at the same time each sidereal day.

Another way to understand this difference is to notice that, relative to the stars, as viewed from Earth, the position of the Sun at the same time each day appears to move around Earth once per year.  A year has about 36'''5'''.24 solar days but 36'''6'''.24 sidereal days. Therefore, there is one fewer [[solar day]] per year than there are sidereal days, similar to an observation of the [[coin rotation paradox]].<ref>{{cite journal|last=Bartlett|first=A. K.|url=http://adsabs.harvard.edu/full/1904PA.....12..649B|title=Solar and Sidereal Time|journal=[[Popular Astronomy (US magazine)|Popular Astronomy]]|year=1904 |volume=12|pages=649–651|bibcode=1904PA.....12..649B }}</ref> This makes a sidereal day approximately {{sfrac|365.24|366.24}} times the length of the 24-hour solar day.