THE LAND OF MID-NIGHT SUN

That is Norway. The sun never sets in Norway during some winter days. Why, because earth is not spinning vertically. It is always tilted (23 degree) towards the sun or away from the sun. Hence, in arctic and Antarctic, there is complete day light or darkness for every six months. Norway is placed close to arctic. There sunset merges into sunrise, with no darkness in between at some period during the year.

In Miami, the shortest day is only 97 minutes longer. Those who live near the equator are lucky. They get more or less 12 hours of sun light throughout the year.
There is a formula to calculate the hours of sunlight you get in a particular day and in particular place on earth.

C = tan(L) * tan (23*cos (360/365*t))
Hours of day light = 24/180 * arccos (C)
L = Latitude
t= Number of days after winter equinox (around 21 December in the northern hemisphere and around 21 June in the south.)

Note: arc cos means inverse of cos. If you get C as +1, your place will receive day light throughout 24 hours on that day. If C is -1, it will be darkness for 24 hours. This will happen in the poles only. Most of us live between the poles.

     Let us take Rio de Janerio (34 degree south of the equator.) How many hours of day light it will get 60 days after equinox?
C= tan (34) *tan (23*cos(360/365 *60))
=0.14; between +1 and -1
Hours of day light = 24/180*arc cos (0.14)
                                  = 10.92 hours
=11 hours of day light.
    Here trigonometry is highly useful.

Note: C is the distance at your latitude, between the 'terminator' - the line that divides day from night - and the earth's axis, scaled to the radius of the circle you revolve in. If you understand this, you are lucky.

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