Today is the longest day of the year—in the Northern Hemisphere, anyway. Fifteen hours and forty minutes of daylight in New York. Seventeen and a half in Copenhagen and Moscow. Twenty-one and change in Reykjavík. Twelve hours, eight minutes, and twenty-four seconds in Kampala, just north of the equator. (The day will be one second shorter there starting next week.) The solstice is the one day when every point north of the Arctic Circle sees at least twenty-four hours of continuous sunlight,but farther north, in Deadhorse, Alaska, on the edge of the Arctic Ocean, the sun rose on May 15th and won’t set again until July 28th. I was in the region once, in late June, with an encampment of biologists on the shore of a glacial lake, and even at two-thirty in the morning, a sliver of sun was visible on the horizon, and the light in the sky was as pale and glassy as the surface of the water. It’s immortality we’re reaching for—the farthest we’ll ever get, once a year, from perpetual night.
So it’s a good moment to note how good we have it here on Earth. There are longer days in our solar system, but none are quite so pleasant. If “day” refers to the time it takes for a planet to rotate exactly once on its axis (a sidereal day), then the Venusian day is the longest, lasting two hundred and forty-three Earth days. That’s even longer, by nineteen Earth days, than a Venusian year, which is the time it takes the planet to orbit the sun. If, instead, “day” refers to the period between sunrise and sunset (a solar day), Neptune’s is the longest: the gas giant orbits the sun on its side, such that one pole or the other receives daylight for forty-two years non-stop.
Farther out in the universe, the days are longer still…
Read the whole essay here.