It's the funniest thing. We've had this discussion before, and I still don't get it.
I know our seasons come about because of the tilt of the earth's axis roughly 25.5 degrees, and I know "the sun doesn't set above the Artic Circle" in high summer. Yet as I visualize the sun "moving south" from the summer solstice to the autumn equinox, I still don't get why it doesn't get dark earlier "up north." It still seems counterfactual to me, even though I observed the phenomenon first had when I made my big cross-country train trip. It was later in the summer, and when the train stopped in northern Montana, it was light later in the evening than it would be back home.
Maybe what I should do is the old science class trick of sticking a pencil through a styrofoam ball and moving it around a light bulb. Then I have to make sure I have the pencil tilted enough and in the right direction.
I think at least part of the explanation is that at the solstice, the days are longer farther north. So on June 21, the sun sets at 8:33 in Philadelphia, 9:03 in Minneapolis and 11:43 in in Anchorage. Daylight in northern cities must shrink more quickly after June 21, though. By Sept. 22 everybody's got 12 hours. Then northern daylight keeps shrinking faster until Dec. 21 -- although, weirdly, at that point sunsets in Philadelphia are only 5 minutes later than Minneapolis (3:34 and 4:39 respectively, but sunRISES are earlier in Philadelphia. Anchorage sunset on Dec. 21 is 3:41 p.m.
These times are affected not just by longitude but also by latitude -- that is, where the city is located within the time zone.