When in doubt. Wikipedia
https://en.wikipedia.org/wiki/High_Noon_(disambiguation)
"High noon, a synonym for Solar noon"
https://en.wikipedia.org/wiki/Noon#Solar_noon
"Noon (also midday or noon time) is usually defined as 12 o'clock in the daytime. The term midday is also used colloquially to refer to an arbitrary period of time in the middle of the day. Solar noon is when the sun crosses the meridian and is at its highest elevation in the sky, at 12 o'clock apparent solar time. The local or clock time of solar noon depends on the longitude and date.[1] The opposite of noon is midnight.
In many cultures in the Northern Hemisphere, noon had ancient geographic associations with the direction "south" (as did midnight with "north" in some cultures). Remnants of the noon = south association are preserved in the words for noon in French (Midi) and Italian (Mezzogiorno), both of which also refer to the southern parts of the respective countries. Modern Polish, Belarusian, Ukrainian, and Serbian go a step farther, with the words for noon (południe, поўдзень, південь, пoднe – literally "half-day") also meaning "south" and the words for "midnight" (północ, поўнач, північ, пoнoħ – literally "half-night", as with English mid(dle) meaning "half") also meaning "north"."
"Solar noon is the moment when the sun transits the celestial meridian – roughly the time when it is highest above the horizon on that day ("Sun transit time"). This is also the origin of the terms ante meridiem (a.m.) and post meridiem (p.m.) as noted below. The sun is directly overhead at solar noon at the Equator on the equinoxes, at the Tropic of Cancer (latitude 23°26′13.7″ N) on the June solstice, and at the Tropic of Capricorn (23°26′13.7″ S) on the December solstice. In the Northern hemisphere, above the Tropic of Cancer, the sun is directly to the south of the observer at solar noon, and in the Southern hemisphere, below the Tropic of Capricorn, it is directly to the north.
The elapsed time from local solar noon of one day to the next day is exactly 24 hours only four instances in any particular year. This occurs when the effects of Earth’s obliquity of ecliptic and its orbital speed around the Sun offset each other. These four days for the current epoch are centered about Feb 11, May 13, July 25 and Nov 3.
It occurs at only one particular line of Longitude each event. This line varies year to year since Earth’s true year is not an integer number of days, not even with the leap year corrections. This event time and location also varies due to Earth’s orbit being gravitationally perturbed by the Planets.
These four 24-hour days occur in both N and S hemispheres simultaneously. The precise UTC times for these four days also mark when the opposite line of longitude 180 degrees away experiences precisely 24 hours from local midnight to local midnight the next day. Thus four varying great circles of Longitude define from year to year when a 24-hour day (noon to noon or midnight to midnight) occurs.
The two longest time spans from noon to noon occur twice each year around Jun 20 (24 hours plus 13 seconds) and around Dec 21 (24 hours plus 30 seconds).
The shortest time spans occur twice each year around March 25 (24 hours minus 18 seconds) and around Sept 13 (24 hours minus 22 seconds)."
Posted: 19 Jun 2016, 10:06