Editing Ecliptic (section)

==Equinoxes and solstices==
[[File:Optical effect march sunset - NOAA.jpg|thumb|upright=1.3|At [[Earth's poles]] the Sun appears at the horizon only and all day around [[equinox]], marking the change between the half year long [[polar night]] and [[polar day]]. The picture shows the [[South Pole]] right before March equinox, with the Sun appearing through [[refraction]] despite being still below the horizon.]]

{| class="wikitable" style="float: right;margin:0em 0 .5em 1em;"
|+'''Positions of [[equinox]]es and [[solstice]]s'''
| rowspan="2" bgcolor="#F4C2C2"|&nbsp;
| align="center" bgcolor="#F4C2C2" | '''[[ecliptic coordinate system|ecliptic]]'''
| align="center" bgcolor="#F4C2C2" | '''[[equatorial coordinate system|equatorial]]'''
|- align="center" bgcolor="#F4C2C2" 
| longitude
| [[right ascension]]
|- align="center"
| bgcolor="#F4C2C2" | '''[[March equinox]]'''
| 0°
| 0h
|- align="center"
| bgcolor="#F4C2C2" | '''[[June solstice]]'''
| 90°
| 6h
|- align="center"
| bgcolor="#F4C2C2" | '''[[September equinox]]'''
| 180°
| 12h
|- align="center"
| bgcolor="#F4C2C2" | '''[[December solstice]]'''
| 270°
| 18h
|}
{{main|Equinox (celestial coordinates)}}

The exact instants of [[equinox]]es and [[solstice]]s are the times when the apparent [[ecliptic coordinate system|ecliptic longitude]] (including the effects of [[aberration of light|aberration]] and [[nutation]]) of the [[Sun]] is 0°, 90°, 180°, and 270°. Because of [[perturbation (astronomy)|perturbations]] of [[Earth's orbit]] and anomalies of [[Gregorian calendar|the calendar]], the dates of these are not fixed.<ref>Meeus (1991), chap. 26</ref>