Why does Seattle's latest sunset occur after the solstice?

I started wondering the same thing recently; it's not just Seattle.

In Seattle, the latest sunset is around the 25th, and the earliest sunrise is around the 15th. Where I live, the latest sunset is around the 30th, and the earliest sunrise is around the 10th (of June). The difference is even greater in December; Seattle's earliest sunset is Dec. 10, and the latest sunrise is on New Year's.

It has to do with the variables that affect the length of the day, such as the varying speed of the earth in its orbit. The different variables are calculated together in what they call the "equation of time", which, when graphed, shows you for each day the difference between usual local noon and the actual middle of the day. It's the same offset you see illustrated on an analemma on a globe.

So, bottom line, it's because we measure time as if every day were exactly 24 hours long, which is the average length of a day, while in reality the day ranges from 23:45 to 24:15 in length.