Why the autumn equinox isn’t actually when day and night are equal | Summer
That’s it for summer. The season ends in the northern hemisphere this week on September 22 while we enter the fall.
The moment is marked by the autumn equinox, which is the moment when the sun crosses the celestial equator, moving south and the days become shorter than nights. The exact moment that occurs is 19:19 BST on September 22 and it is caused by the movement of the earth along its orbit, gradually tilting the northern hemisphere of the sun.
The name Equinox comes from the Latin aequus, which means equal and nox, which means night. Therefore, it is said that the equinox is when the day and night have the same length, which would be true if the earth had no atmosphere.
The effect of the air that we breathe is to fold the sunlight, so we see our star parent on the horizon before it really raised, then again after its bet. This gives a few additional minutes of daylight to the equinox.
A few days later, the durations of the day and the night are really equal. This is known as Equilux and occurs on September 25 or 26 depending on your precise location.
