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:
“Sometimes, because of its immediacy, television produces a kind of electronic parable. Berlin, for instance, on the day the Wall was opened. Rostropovich was playing his cello by the Wall that no longer cast a shadow, and a million East Berliners were thronging to the West to shop with an allowance given them by West German banks! At that moment the whole world saw how materialism had lost its awesome historic power and become a shopping list.”
—John Berger (b. 1926)
“O Cressida! But that the busy day,
Waked by the lark, hath roused the ribald crows,
And dreaming night will hide our joys no longer,
I would not from thee.”
—William Shakespeare (1564–1616)