APOD: 2019 September 23 - Equinox: The Sun from Solstice to Solstice

Good morning, Rallypoint. Today's Astronomy Picture of the Day (APOD) is titled "Equinox: The Sun from Solstice to Solstice." Today marks the Autumnal Equinox in the Northern Hemisphere (or Vernal Equinox below the Equator). An equinox is commonly regarded as the instant of time when the plane (extended indefinitely in all directions) of Earth's equator passes through the center of the Sun. The word is derived from the Latin aequinoctium, from aequus (equal) and nox (genitive noctis) (night). On the day of an equinox, daytime and nighttime are of approximately equal duration all over the planet.

The day of a solstice in either hemisphere has either the most sunlight of the year (summer solstice) or the least sunlight of the year (winter solstice) for any place other than the Equator. The word solstice is derived from the Latin sol ("sun") and sistere ("to stand still"), because at the solstices, the seasonal movement of the Sun's daily path (as seen from Earth) stops at a northern or southern limit before reversing direction.

Our featured picture is a composite of hourly images taken of the Sun above Bursa, Turkey on key days from solstice to equinox to solstice. The Sun would follow the middle arc today (and in March), be at the upper arc in June, and the lower arc in December. For our friend Cynthia Croft, the upper solar arc would happen in December, and the lower in June.