The transition from summer to autumn is usually marked by cool breezes and leaves changing color, though officially, fall does not begin until the autumnal equinox.
The Earth is split by the the equator into northern and southern hemispheres. According to National Geographic, the planet orbits the sun at an tilted angle of approximately 23.5-degrees, and it is this tilt that determines the seasons.
When it’s winter in the north, that area is tilted away from the sun. When it’s summer, it’s tilted towards the sun. Because of this tilt, day and night times are not usually equal, except on the two annual equinox days, writes The Weather Network.
According to the BBC, the autumnal equinox occurs every year, usually on September 22, 23, or 24. Equinox is latin for ‘equal night’, and marks the moment when the sun passes over the equator. In spring, this is known as the vernal equinox, while in fall, we know it as the autumnal equinox. On these days, daylight and nighttime are both 12 hours long.
Since fall also signals harvest season, many festivals are celebrated around this time. The Chinese have the Mid-Autumn Festival, while the Jewish have Sukkot or the Feast of Tabernacles.
1. Earth relative to the sun
2. Earth’s orbit around the sun showing change in seasons
3. Exact moment of autumnal equinox
4. Date and time of autumnal equinox