Lomé, Togo is located about 5° N Latitude. Because it is so
close the equator, the length of a day and the length of a night are about the
same year-round. At the equator, darkness falls almost instantly after sunset;
there is no twilight. Why? As an amateur astronomer, I wanted to research this.
Here is what I found out:
The earth is rotating on its axis. It
rotates once every 24 hours and the earth is about 24,000 miles in
circumference. So at the equator, the earth is turning at about 1000 miles per hour.
At the poles, the surface speed is nearly zero. At this speed, the sun rises
and sets very quickly. You do not notice the speed of the earth on the surface,
but the sun appears to rise and set rapidly. At or near the equator, the sun
rises at about 6AM and sets at about 6 PM every day of the year. In the morning,
at 6 AM, it is almost totally dark. By 6:30 AM, the sun is up and full daylight
is everywhere. Similarly in the evening, it is daylight at 6 PM and dark at
6:30. The sun "plunges" below the horizon at a steeper angle,
therefore it gets dark quicker.
Furthermore, at low latitudes (near the equator), the sun
sets perpendicular to the horizon, while at higher latitudes, the sun can set
at a more oblique angle, allowing it to remain close to the horizon after
sunset for a longer period of time.
When the sun sets in the north, it "disappears"
over the horizon in a sharp angle. So it takes a while for the "whole
disc" to disappear. So a big part of its movement is about going along the
horizon, not about setting. Therefore, it sets slower.
In extreme cases (summer in the Arctic) it never completely
disappears but just hugs the horizon.
At the equator, this angle is about 90 degrees. So the sun goes over the horizon straight down rather than in an angle.
If you're near the poles, the Sun sets in a skew angle
relative to the horizon.
Yes, it does change from day to night, and vice versa,
faster near the equator (actually in the Torrid Zone between the Tropics of
Cancer and Capricorn). The reason is at those latitudes, the sunlight passes
through less of earth's atmosphere than at high latitudes. The angle of the
sun's descent toward the horizon is closer to the perpendicular, and for those
two reasons, (a) the sun's light is refracted less at lower latitude, and (b)
the sun "plunges" below the horizon at a steeper angle, therefore it
gets dark quicker.
On the two equinox days (March 21, the first day of spring,
and September 21, the first day of autumn), the whole world gets 12 hours of
daylight and 12 hours of darkness. On those days, it's the same in Colorado, on
the Equator, and in Australia.
