The number of sunrises and sunsets is not the same in the world

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

23 February 2020

Schools were on mid-term break the past week and I was roped-in to help a primary school pupil revising her social studies. The topic was latitudes of the earth. First, I wanted to know how much she knows and so I asked her to tell me the significance of the equator.

She said that it is an imaginary line that marks where the sun travels. Well, that might sound correct, but is isn’t! The equator does not mark the path of the sun.

It signifies the halfway distance from pole to pole. If you cut the planet along the equator, you will end up with two equal halves – well, almost equal. My next question was about the tropics: what do they signify?

Her answer was: “they are the farthest north and south that the sun goes during one year”. She also knew that the sun is at its northern-most position (tropic of Cancer) in June and southern-most (tropic of Capricorn) in December.

What she didn’t know is that the two tropics mark the only region on earth that the sun can be seen directly overhead – at noon. People who live outside the tropics never ever see the sun directly above their heads!

This was shocking news for the girl! “You mean to say that the people of England don’t ever see the sun overhead?”, she asked.

That is correct: viewed from London, for example, the highest the sun can go is about 63 degrees above the horizon. That happens only once in the year – on June 21st, which marks midsummer. The rest of the year it reaches “lower” positions.

And that’s not all: the farther outside the tropics you go, the lower the highest position in the sky the sun reaches. At the north pole, the sun rises only up to 23.5 degrees.

Things get very interesting at the poles. First of all, East and West do not exist! So, where does the sun rise and set? The answer is that, at the poles, there is only one sunrise and one sunset in the year!

For the North Pole, the sun begins to rise on March 21. It continues rising for three months without setting at all. It reaches it highest point (23.5 degrees above the horizon) on June 21 and then it starts setting…again continuously over a period of three months. On September 23, it sets and is not seen again for six months until March 21 the following year.

During the six months from March to September, a person at the North Pole will see the sun going around the sky along the horizon; in a clockwise direction and completing one cycle every 24 hours.

As we move towards the tropics, we soon come to a region where they see two sunrises and sunsets in a year. The numbers increase gradually and, eventually, we reach what we are accustomed to: 365.

This number is reached at latitude 66.5 degrees. It is known as the Arctic Circle (in the North) or the Antarctic Circle (in the South). Starting from the equator, it marks the point where the number of sunrises and sunsets in one year is less than 365.