Editing Culmination (section)

==Period of time==
{{see also|Sidereal time|Equation of time|Perturbation (astronomy)}}
The period between a culmination and the next is a [[sidereal day]], which is exactly 24 [[sidereal time|sidereal hours]] and 4 minutes less than 24 common [[solar hour]]s, while the period between an upper culmination and a lower one is 12 sidereal hours. The period between successive day to day (rotational) culminations is effected mainly by [[Earth's orbit]]al [[proper motion]], which produces the different lengths between the [[solar day]] (the interval between culminations of the Sun) and the sidereal day (the interval between culminations of any [[fixed stars|reference star]]) or the slightly more precise, [[precession]] unaffected, [[stellar day]].<ref name="US Naval Observatory Astronomical Applications Department 2023">{{cite web | title=Sidereal Time | website=US Naval Observatory Astronomical Applications Department | date=2023-06-02 | url=https://aa.usno.navy.mil/data/siderealtime | access-date=2023-06-02}}</ref> This results in culminations occurring every solar day at different times, taking a [[sidereal year]] (366.3 days), a year that is one day longer than the [[solar year]], for a culmination to reoccur. Therefore, only once every 366.3 solar days the culmination reoccurs at the same time of a solar day, while reoccurring every sidereal day.<ref name="Encyclopedia Britannica 1998">{{cite web | title=Calendar - Sidereal Day, Synodic Month, Tropical Year, Intercalation | website=Encyclopedia Britannica | date=1998-07-20 | url=https://www.britannica.com/science/calendar | access-date=2023-06-02}}</ref> The remaining small changes in the culmination period time from sidereal year to sidereal year is on the other hand mainly caused by [[Astronomical nutation|nutation]] (with a 18.6 years cycle), resulting in the longer time scale [[axial precession]] of Earth (with a 26,000 years cycle),<ref name="Oxford Reference 1999">{{cite web | title=apparent sidereal time | website=Oxford Reference | date=1999-02-22 | url=https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095419792;jsessionid=3FA35A4692C474A698B5EFF99EDC87BC?rskey=xDQN4Z&result=5 | access-date=2023-06-02}}</ref><ref name="Buis Laboratory 2020">{{cite web | last=Buis | first=Alan | last2=Laboratory | first2=s Jet Propulsion | title=Milankovitch (Orbital) Cycles and Their Role in Earth's Climate – Climate Change: Vital Signs of the Planet | website=Climate Change: Vital Signs of the Planet | date=2020-02-27 | url=https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate | access-date=2023-06-02}}</ref>  while [[apsidal precession]] and other mechanics have a much smaller impact on sidereal observation, impacting Earth's climate through the [[Milankovitch cycles]] significantly more. Though at such timescales stars themself change position, particularly those stars which have, as viewed from the [[Solar System]], a [[Proper motion#Stars with high proper motion|high proper motion]].

[[Stellar parallax]] appears to be a similar motion like all these apparent movements, but has only from non-averaged sidereal day to sidereal day a slight effect, returning to its original apparent position, completing a cycle every orbit, with a slight additional lasting change to the position due to the precessions. This phenomenon results from Earth changing position on its orbital path.