It is the summer’s great last heat,
It is the fall’s first chill: They meet.
–Sarah Morgan Bryan Piatt
Autumn begins Friday afternoon at 3:02 p.m., also known as the autumnal equinox.
On the autumnal equinox, day and night are each about 12 hours long (with the actual time of equal day and night, in the Northern Hemisphere, occurring a few days after). On this day, the sun will rise exactly due east and set exactly due west. Earth’s two hemispheres are receiving the Sun’s rays about equally. The Sun is overhead at noon as seen from the equator. At this point, the amount of nighttime and daytime (sunlight) are roughly equal to each other.
Instead of the Earth tilting away from or toward the sun, its axis of rotation becomes perpendicular to the line connecting the centers of the Earth and the sun. This change in the tilt causes the change in seasons with the northern hemisphere moving from the warmth of summer to the chill of winter.
The Old Farmer’s Almanac