Day and Night
The sun at the North Pole is continuously above the horizon during the summer and continuously below the horizon during the winter. Sunrise is just before the March equinox (around March 19); the sun then takes three months to reach its highest point of near 23½° elevation at the summer solstice (around June 21), after which time it begins to sink, reaching sunset just after the September equinox (around September 24). When the sun is visible in the polar sky, it appears to move in a horizontal circle above the horizon. This circle gradually rises from near the horizon just after the vernal equinox to its maximum elevation (in degrees) above the horizon at summer solstice and then sinks back toward the horizon before sinking below it at the autumnal equinox.
A civil twilight period of about two weeks occurs before sunrise and after sunset, a nautical twilight period of about five weeks occurs before sunrise and after sunset and an astronomical twilight period of about seven weeks occurs before sunrise and after sunset.
These effects are caused by a combination of the Earth's axial tilt and its revolution around the sun. The direction of the Earth's axial tilt, as well as its angle relative to the plane of the Earth's orbit around the sun, remains very nearly constant over the course of a year (both change very slowly over long time periods). At northern midsummer the North Pole is facing towards the sun to its maximum extent. As the year progresses and the Earth moves around the sun, the North Pole gradually turns away from the sun until at midwinter it is facing away from the Sun to its maximum extent. A similar sequence is observed at the South Pole, with a six-month time difference.
Read more about this topic: North Pole
Famous quotes containing the words day and/or night:
““If Washington were President now, he would have to learn our ways or lose his next election. Only fools and theorists imagine that our society can be handled with gloves or long poles. One must make one’s self a part of it. If virtue won’t answer our purpose, we must use vice, or our opponents will put us out of office, and this was as true in Washington’s day as it is now, and always will be.””
—Henry Brooks Adams (1838–1918)
“‘Tis said of love that it sometimes goes, sometimes flies; runs with one, walks gravely with another; turns a third into ice, and sets a fourth in a flame: it wounds one, another it kills: like lightning it begins and ends in the same moment: it makes that fort yield at night which it besieged but in the morning; for there is no force able to resist it.”
—Miguel De Cervantes (1547–1616)