Yes, people have been drinking pumpkin spice lattes for a month now. But fall doesn't begin officially until tonight, when autumnal equinox arrives. That means shorter days, cozy sweaters, and of course brilliant foliage.
But have you ever wondered why leaves change color in the fall, and why they turn so many different hues, from yellow and orange to crimson and finally to brown?
As a new American Chemical Society video explains, it's all about the activity of chlorophyll, a pigment that makes leaves green and which plays a critical role in photosynthesis.
Check out the video above, which is the latest installment in the society's Reactions YouTube series. Happy Autumn!