As Darkness Falls

This week celebrates the first official day of summer. Northeast Pennsylvania has finally reached a point where I can wear dresses and sit on the porch. People are cutting grass, cooking out, and enjoying the beautiful weather. That's not dependent on the calendar, necessarily, but June 21 marks the longest day of the year.

Do you enjoy the twilight, that in-between time, the window between sunset and full dark? Have you always lived in the same place? If not, or if you've had the ability to travel to a place far away, you may have noticed an interesting phenomenon.

Closer to the equator, twilight is so short as to be almost non-existent. The farther from the equator, the longer the twilight.

This has to do with the rotation of the earth and the angle of the sun's rays to it. At the equator, the sun is perpendicular, almost straight up and down. As you move farther from the equator, the sun's angle becomes more oblique, so the light lasts longer as the earth rotates.

This makes sense when you think about it. We know that Alaska and Canada and Russia, above the Artic Circle, have six months of light, when the sun never sets. Or, if it sets, the twilight never turns to dark. Essentially, their "twilight" is lasting for hours. As you move slightly southward, twilight will end a little sooner, and a little sooner, and so on, until you reach the equator and the transition from sunset to dark is almost instantaneous.

I enjoy these little nuggets of knowledge, but I realize most people don't care to know the whys and wherefores. Whether you do or don't, I hope you'll enjoy the longest day this week, the first day of summer!