Editing Equation of time (section)

=== Obliquity of the ecliptic ===
[[Image:Middaysun.gif|thumb|upright|right|Sun and planets at local apparent noon (Ecliptic in red, Sun and Mercury in yellow, Venus in white, Mars in red, Jupiter in yellow with red spot, Saturn in white with rings).]]

Even if the Earth's orbit were circular, the perceived motion of the Sun along our [[celestial equator]] would still not be uniform.<ref name="jenkins" /> This is a consequence of the tilt of the Earth's rotational axis with respect to the [[orbital plane (astronomy)|plane of its orbit]], or equivalently, the tilt of the [[ecliptic]] (the path the Sun appears to take in the [[celestial sphere]]) with respect to the [[celestial equator]]. The projection of this motion onto our [[celestial equator]], along which "clock time" is measured, is a maximum at the [[solstice]]s, when the yearly movement of the Sun is parallel to the equator (causing amplification of perceived speed) and yields mainly a change in [[right ascension]]. It is a minimum at the [[equinox]]es, when the Sun's apparent motion is more sloped and yields more change in [[declination]], leaving less for the component in [[right ascension]], which is the only component that affects the duration of the solar day. A practical illustration of obliquity is that the daily shift of the shadow cast by the Sun in a sundial even on the equator is smaller close to the solstices and greater close to the equinoxes.  If this effect operated alone, then days would be up to 24&nbsp;hours and 20.3&nbsp;seconds long (measured solar noon to solar noon) near the solstices, and as much as 20.3&nbsp;seconds shorter than 24&nbsp;hours near the equinoxes.<ref name=rmg/><ref>{{cite web|title=Obliquity|url=https://analemma.com/obliquity.html|website=Analemma|access-date=29 January 2021}}</ref><ref name=moonkmft/>

In the figure on the right, we can see the monthly variation of the apparent slope of the plane of the ecliptic at solar midday as seen from Earth. This variation is due to the apparent [[precession]] of the rotating Earth through the year, as seen from the Sun at solar midday.

In terms of the equation of time, the inclination of the ecliptic results in the contribution of a sine wave variation with:

* amplitude: 9.87 minutes
* period: 1/2 year
* zero points: equinoxes and solstices
* extreme values: beginning of February and August (negative) and beginning of May and November (positive).

This component of the EoT is represented by the aforementioned factor "b":

<math>b = 
9.863\sin \left( 2 (6.240\, 040\, 77 + 0.017\, 201\, 97 (365(y-2000)+ d)) + 3.5932 \right)</math>