The Sun, which is shown setting behind the Davis Mountains near McDonald Observatory, sets earliest for the year from the northern United States in mid-December. The earliest sunsets for more southerly latitudes took place earlier in the month.
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The shortest day of the year is still almost a week away, yet for most of the country, the Sun is already starting to set a little later than it did just a few days ago. The difference isn’t much, though — you have to pay close attention to notice it.
The shortest day of the year is the winter solstice. In the northern hemisphere, it comes on December 21st, when the Sun stands farthest south for the entire year.
You might expect the latest sunrise and earliest sunset on the solstice as well. But that’s not the case. The earliest sunsets came around the first of December for those in Miami, about a week later for those in the country’s middle latitudes, and a few days later still for those in the north.
There are several reasons for the early sunsets. One is related to Earth’s tilted axis. Another is Earth’s orbit around the Sun.
Right now, we’re near our closest point to the Sun, so our planet moves a little quicker and covers a slightly greater distance than average each day. That means that Earth has to turn a little bit farther for the Sun to return to “local noon” each day — its highest point in the sky. And that takes a bit more time, so local noon occurs later each day. And if noon comes later, so do sunrise and sunset.
If you add it up, the earliest sunsets take place a few days or weeks before the solstice, while the latest sunrises occur after the solstice. It’s all part of the precise but complicated workings of the solar system.
Script by Damond Benningfield, Copyright 2014