These occur when the sun passes directly over the equator. On these two days, day and night are roughly equal in length everywhere on Earth.
If you’d like, I can also provide (JavaScript/Python/Swift) for calculating the exact equinox/solstice times. Just tell me your target platform.
Ancient cultures viewed this day with a mix of dread and hope. While it marked the beginning of "the deep cold," it also meant that the sun was "returning," as each subsequent day would be slightly longer than the last. Why Do the Dates Shift? first day of seasons
You might notice that the first day of a season isn’t on the same date every year. This is because a "year" isn't exactly 365 days; it actually takes the Earth about 365.242 days to orbit the sun. Our calendar accounts for this with Leap Years, which causes the astronomical timing of the solstices and equinoxes to drift slightly between the 20th and 23rd of their respective months.
(The Human Element)
Why do meteorologists often say winter starts on December 1st, while the calendar says December 21st?
| Case | Handling | |------|-----------| | Near a season start (<1 day) | Show exact hours/minutes | | Exact season start day | Show “Today at 10:46 AM” | | Different hemisphere while traveling | Offer manual override or detect via GPS | | Leap years / Gregorian drift | Use astronomical calculation, not fixed calendar dates | These occur when the sun passes directly over the equator
# Pseudocode def next_season_start(now, hemisphere): events = get_equinoxes_and_solstices(now.year, now.year+1) for date, season_name in events: if date > now: return "season": season_name, "datetime": date, "days_until": (date-now).days