Why a day at the poles lasts one year
The Sunday Nation
Nairobi,
07 February 2010
After reading last week’s article, Justin Ose came up with three questions. First, he asks, “Does the earth move at same speed that is (1,667 km/h) all around all over the north and south poles?”
The answer is no. The reason is that the Earth rotates about an axis that joins the north and south poles. (Now, don’t start thinking that there is a long axel holding the planet in place!) Consequently; the closer you are to the poles the slower you rotate.
This however does not mean that you get a longer day near the poles. No, it is still 24 hours, but the “circuit” completed is shorter hence the slower speed (distance covered divided by time taken).
Justin’s second question is: “Is there some place on planet earth, where there is six months of darkness (NIGHT) and six months of light (DAY)?” Yes: At the poles. This is happens because the Earth’s axis of rotation is tilted away from the axis of revolution (motion around the sun).
These two axes are about 23.5 degrees to each other. This is why we see the path of the sun across the sky swinging north-to-south-to-north as the year progresses. At the poles, the concept of a day is very different from what we are used to.
As the summer approaches, the sun rises and travels in a circular path along the horizon, gradually rising higher until it reaches about half-way up the sky (never gets overhead). It then descends slowly back below the horizon. This rising takes about three months and the setting another three months - half a year in total.
During the six months of daylight, the sun takes 24 hours to complete one cycle round the horizon. After setting, it remains below the horizon, unseen for another half year. Throughout this time, it is visible at the other pole on the opposite side of the planet doing the same circulation along the horizon.
Therefore, if we define “a day” as the duration from “sunrise to sunset to sunrise”, we can then say that a day at the poles lasts one year. If you find that difficult to conceptualise, then bear in mind that at the North Pole, every direction is south; and from the South Pole, every direction is north!
Justin’s third question is straightforward: “Is it true that pace of the earth spin is reducing and that at one time it will come to stand still and life will stop on the blue marble?”
Yes! The Earth is slowing down, but very slowly. The duration for one rotation (one day) increases by about one millisecond every century! So it’s going to take very many years before the Earth stops rotating.
As to whether life on Earth will come to an end, I don’t think so. Since the change is happening very slowly, I think the living organisms on the planet will gradually adapt to the slow down.
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