Dates and Times of the Seasons Calculator
For Gregorian Years 1600 to 2200
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 Dates and Times of Northern/Southern Seasons for the Year 2017 

NORTHERN SOUTHERN  Year  Date  DoW    Time TT      Delta T
 Spring   Autumn   2017 Mar 20 Mon at  10:30      +01m 10s
 Summer   Winter   2017 Jun 21 Wed at  04:25      +01m 10s
 Autumn   Spring   2017 Sep 22 Fri at  20:04      +01m 10s
 Winter   Summer   2017 Dec 21 Thu at  16:29      +01m 11s
TT Time Scale,     ΔT estimates based on the NASA Polynomials for ΔT
Solar coordinates based on the Full-Precision VSOP87 Theory, Series C IAU 2000B Nutation Series

NOTE:


Definitions of the Solstices and Equinoxes Used Here

The dates and times of the Northern/Southern solstices and equinoxes are computed according to the following definitions:

The solstices refer to that point in the sky where the sun appears to reach its highest or lowest midday elevation in the sky and where it appears to hover for a day or so before slowing starting to move back in the opposite direction, southward or northward, depending on the season, a little more each day.  There are two solstices each year which mark the dates on which the summer and winter seasons begin.

The equinoxes refer to those dates of the year where the days and nights throughout the world are most closely equal in length (closer to 12h/12h) than on any other date of the year.  There are two equinoxes each year marking the dates on which the spring and autumn seasons begin and the apparent geocentric sun crosses the celestial equator.

Let:   Blue Seasons = Northern hemisphere and Red Seasons = Southern hemisphere
  • Spring/Autumn - Equinox
    Begins at the moment when the apparent geocentric sun reaches declination = 0°

    Sun crosses equator from south to north.




  • Summer/Winter - Solstice
    Begins at the moment when the apparent geocentric sun reaches RA = 06h (90°).

    Sun appears stationary at northernmost latitude (approx. +23.45°), before heading
    back south a little more each day.




  • Autumn/Spring - Equinox
    Begins at the moment when the apparent geocentric sun reaches declination = 0°

    Sun crosses celestial equator from north to south.




  • Winter/Summer - Solstice
    Begins at the moment when the apparent geocentric sun reaches RA = 18h (270°).

    Sun appears stationary at southernmost latitude (approx. -23.45°), before heading
    back north a little more each day.






USNO-Ref: (Tries to open in a new tab)
http://aa.usno.navy.mil/data/docs/EarthSeasons.php




PHP Science Program by Jay Tanner - 2017 - v2.75