TILOTD - Autumn Equinox

TILOTD -- Things I Learned On This Day

Autumn Equnox - Sept 22, 2025

• The autumn equinox marks the first day of fall in the Northern Hemisphere. It occurs when Earth's axis is not tilted toward or away from the sun, resulting in nearly equal day and night lengths.
• The exact date of the equinox can vary between Sept. 21 and Sept. 24 due to the Gregorian calendar's approximation of the Earth's orbit around the sun.
• Cultural celebrations take place worldwide on the equinox. That day is also a key period for observing natural phenomena like the Northern Lights due to increased geomagnetic activity
• The autumn equinox is really just a moment in time -- to be exact it's when the sun crosses the celestial equator, an imaginary line in the sky above Earth's equator.
• Normally, Earth orbits tilted on its axis by 23.5 degrees. But at precise instant of the Autumnal equinox, its rotational axis is neither tilting toward nor away from the sun.
• People in the Southern Hemisphere refer to September equinox as the spring equinox, a signal that the days will start getting longer.
• The word "equinox" comes from the Latin aequus (meaning "equal") and nox (meaning "night") but day and night are not exactly 12 hours each on the day of the equinox.
• Earth takes 365.25 days to go around the sun. So, this means that the September equinox will be six hours later than it was the year before. (The inclusion of leap years sort of resets the date.)
• The equinoxes bring on the Northern Lights Auroras all the way through the spring equinox each March.
• Auroras are caused by the interaction of solar winds with Earth's magnetic field. The solar winds are particles of plasma escaping from the sun and into space. Due to Earth's axial tilt, the solar wind from the sun is better able to reach Earth's atmosphere through our geomagnetic field. These disturbances in Earth's magnetic field (called geomagnetic storms) are therefore at their strongest in the spring and fall, compared to summer and winter.
• The particles that slam into Earth's magnetic field collide with atoms of oxygen, nitrogen, and other elements in the air. These particles eventually release photons of different wavelengths and therefore the different colors of aurora you can see in the sky.
• There are several celebrations associated with the fall equinox. For instance, there's the neopagan festival of Mabon a harvest festival to celebrate the gathering of crops and the bounty of the earth.
• China and other Asian countries celebrate the moon festival which is always held in mid-September, around the time of the harvest moon. The harvest moon is the full moon closest to the autumnal equinox.

Source: https://science.howstuffworks.com/environmental/earth/5-things-didnt-know-about-spring-equinox.htm