And the first day of winter in the southern hemisphere. At this solstice, the north pole has a midnight sun, and the south pole has darkness all day long. We have a solstice because Earth is tilted on its axis. As we travel around the sun, the northern and southern hemispheres trade places in receiving the most direct rays of sunlight. That's because, in early July, Earth always reaches its aphelion, or farthest point from the sun.
Earth moves slightly more slowly when it's farthest from the sun.
So slightly more time passes between the June solstice and September equinox than between any other solstice and equinox. Watch for the path of the sun today across the sky. Also, look for your shadow at noon. If you're on the northern half of the globe, it'll be your shortest noontime shadow for the year. With thanks to the National Science Foundation, we're Block and Byrd for Earth and Sky.