How long does a sunrise or sunset take?
From the time that the sun appears on the horizon, or meets it on its setting, to the time that it is fully visible, or no longer visible on its setting, how much time passes?
Secondly, is there a place in the world where a sunrise/sunset occurs over a period of a few days? Meaning, that from the time it begins to appear over the horizon until it is fully visible, a period of a few days pass without night intervening (and the same for the opposite with sunset)?
At the equator, the sun seems to rise and set quickly - as Rudyard Kipling says, "On the road to Mandalay, Where the flyin'-fishes play, An' the dawn comes up like thunder outer China 'crost the Bay!" While the farther North or South you go, sunset lingers more and more. Summer sunsets in Georgia seem to take 15 minutes or so to ease under the covers of the darkening land.
The time it takes depends on various factors: the angle that the path of the sun makes with the horizon is the main one, though there are also optical effects caused by the atmosphere have an effect too.
Generally the closer to the equator you live, the steeper is the angle, and so the faster is the sunset.
Using Stellarium I did a couple of tests:
- In the UK (50 degrees North) on 10th December, it took the sun 4min 47s seconds to sink below a simulated horizon.
- In Angloa (10 degrees south), on the same day it took 2min 26s for the sun to set.
It seems that in most populated regions, a sunset takes between 2 and 5 minutes.
There are locations, close to the Antarctic circle at this time of year, at which the sun merely partially sets, and then rises again. And at the Pole, the sun moves around in horizontal circles in the sky each day. During summer there is a permanent sun, as winter approaches the sun gets closer to the horizon, and then sets over several days. (Randall calculates 38 to 40 hours in the blog that Barry links)