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Dates and Times of Northern/Southern Seasons for the Year 2025  NORTHERN SOUTHERN Year Date DoW Time TT Delta T Spring Autumn 2025 Mar 20 Thu at 09:03 +01m 15s Summer Winter 2025 Jun 21 Sat at 02:43 +01m 15s Autumn Spring 2025 Sep 22 Mon at 18:20 +01m 15s Winter Summer 2025 Dec 21 Sun at 15:04 +01m 15s

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

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NOTE:

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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

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• Spring/Autumn - Equinox
  Begins at the moment when the apparent geocentric sun reaches declination = 0°
  
  Sun crosses equator from south to north.
  
  
  
  

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• 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.
  
  
  
  

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• Autumn/Spring - Equinox
  Begins at the moment when the apparent geocentric sun reaches declination = 0°
  
  Sun crosses celestial equator from north to south.
  
  
  
  

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• 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.
  
  
  
  

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

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