Polar Day

 I'm obviously very late posting this photo of a note left on the community whiteboard here on May 26:

I've had a few friends ask me what time the sun is setting now, and the answer is: it's not! The Arctic Circle is defined by the latitude at which you are far enough north that for at least one night per year (on the summer solstice, if it's only one night), the sun never goes completely below the horizon. And the farther north you go, the more nights there will be without sunsets. The same is true for the winter: at the exact latitude of the Arctic Circle, for one day each winter (on the winter solstice), the sun will not make it above the horizon. The further north you go, the more pronounced the effect gets. 

At Toolik, we are far enough north that the sun won't set for a nearly-two-month period every summer. If you went all the way up to the North Pole, the sun wouldn't set for six months, between the spring and autumn equinoxes--so, only one sunset (on the autumn equinox) and one sunrise (on the spring equinox) per year. 

The same is true for the southern hemisphere, substituting the word south instead of north, and with the seasons reversed in the calendar year. (Which is why, when I spent a full year at the South Pole, we only had one sunset, in late March on the autumn equinox, and then no sun at all for six months until the spring equinox, in September, when the sun came up again and stayed up for the next six months.)

Fun facts!