Computation of day length, amount of energy received over a day and over a year in function of latitude, date and obliquity

Abstract

In these notes, we do the computation of the formula giving the expression of solar energy received by an horizontal section of 1 square meter, relatively to the latitude, obliquity and current day (the quantity is also proportional to the solar flux). We also obtain the formula of energy received during one day, of day length, of the possibility, according to the latitude, to observe the sun at zenith one day in year (and in this case, the formula of the day it happens), the possibility to observe a oplar night/day, and the time of beginning of these phenomenons according to the latitude. Section 1 introduce the 4 different angles which are obliquity, latitude, day and hour. We also introduce the corresponding rotations. In 2, we give the position of the sun in the sky. That make able to compute the day length in 3 Following sections are pairwie independent, except 6 which relies on 5. In4, we compute for which latitudes it is possible to observe or not a polar day or a polar night, and give the time of beginning and en of these lasts. In 5, we intergate between sunrise and sunset the received solar power, which give us the quantity of energy received during one day. In 6, we integrate the following quantity in order to obtain the quantity of energy received per year. In 7, we prove that only latitudes located between tropics can observe sun at zenith, and give the two instants it happens in a year. In 8 we compute the direction of sunrise and sunset, given atitude and day.