[Ads-l] Solstice

[Bill Mullins]

> It appears to me that Merriam-Webster has this defined incorrectly:
>
> https://www.merriam-webster.com/dictionary/solstice <
> https://www.merriam-webster.com/dictionary/solstice>
> either of the two points on the ecliptic at which its distance from the
> celestial equator is greatest and which is reached by the sun each year
> about June 21 and December 21
>
> Does anyone know enough astronomy to know for sure?
>
> Benjamin Barrett
> Formerly of Seattle, WA

That is a poor definition. For example, the antecedent of "its" is not clear.  I assume it is "ecliptic".  And it defines solstices as places, rather than times.  (The Winter/Summer solstice is generally thought of as a date/time of the year, rather than as a point in the Earths' orbit.)

The ecliptic is the plane defined by the Earth's orbit around the Sun.  The Celestial Equator is the plane defined by projecting the Earth's equator infinitely outward.  The Earth's orbit carries it through the two points where these planes intersect on the Equinoxes (beginning of Spring and beginning of Autumn).  The Solstices are the points halfway between the Equinoxes in the ellipse of the orbit.

This illustration from wikipedia is helpful:
https://upload.wikimedia.org/wikipedia/commons/b/bd/Earths_orbit_and_ecliptic.PNG
(although it does not show the solstices).

If I were writing the definition, it would read something like:
"The two times of the Solar year at which the Earth's orbit around the Sun carries it farthest above or below the plane of the Ecliptic."


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