SPOKANE, Wash. — 3:57 PM - That's when the sun sets in Spokane on Dec. 13. It's the earliest of the year. And from here to summer, the sunsets will get later each day.
But wait - isn't the shortest day of the year the winter solstice on Dec. 21? It is! So why doesn't our earliest sunset fall on the same day as the shortest day?The answer lies in Earth's orbit around the sun.
Earth's orbit isn't quite a perfect circle, it's slightly elliptical. And there in lies the answer as to why our earliest sunset isn't on the same day as the solstice. But to better visualize it, you just have to see an image of the Sun's Analemma.
So what's an Analemma? It's the motion the sun makes in the sky if you were to take a snapshot of the Sun's location each day from the same spot at the same time (daylight saving time not included). That motion makes a figured-8 pattern.
If you've ever seen that weird figured-8 diagram on a globe - that depicts the Analemma, too.
Using the diagram above, when the sun is slightly more east in the sky before the first day of the solstice, that's when we get our earliest sunset of the year. For Spokane that's at 3:57 pm between Dec. 9 and 13.
The flip side is also true, our latest sunrises of the year, 7:38 am in Spokane, are just after the Solstice from Dec. 30 to Jan. 3.
One last tid-bit, the closer you are to the Equator, the more separated the dates between earliest sunset/latest sunrise are from the Winter Solstice. For example, in Miami the early sunset is between Nov. 22 to Dec. 7.
And now you know why are earliest sunsets and latest sunrises aren't simply on the same day as the shortest day.