The amount of sun rays the same part the of the earth receives changes throughout the year. The amount solar radiation a place receives at a point in time is called insolation. The insolation is the main source of energy for our planet. The reason why we have seasons is the fluctuations of insolation in your area. The are several cause for the fluctuations. One of those causes is the weather. on a cloudy day less solar radiation is able to get to the surface. But the weather is very unpredictable and affects the total insolation to a minor degree. The two major cause for the fluctuations are the amount of daylight you recieve in day ,and the angle of the solar of the solar rays. The amount of daylight you get determines how much solar radiation you receive in a day. The angle of the solar rays affects the intensity at which you get the solar radiation. The intensity of insolation at a given latitude can be found using lambert’s law which was named after Johann Lambert. The 18th-century German scientist developed a formula by which the intensity can measured by using the sun zenith angle. Using his law you are able to find out based on latitude where a greater amount of solar radiation is received on the surface of the earth. Also the gases in atmosphere act to get rid of, to some extent, the amount of insolation that gets to Earth’s surface.Most people think that the seasons are caused by the distance changing between Earth and the sun during Earth’s yearly orbit around the sun. As said earlier, the change in this distance is very tiny. Furthermore people in the Northern Hemisphere are actually closer to the sun in January and farther away in July. This is completely opposite of the hemisphere’s seasonal variations.As we know the change in seasons is caused by earth’s 23.5° degree tilt. Earth is positioned in a orbit so that the northern tip of its axis is inclined toward the sun at an angle of 23.5°. We imagine Earth rotating under these conditions, a large portion of the Northern Hemisphere remains in daylight than the Southern Hemisphere. Also, a bigger portion of the Southern Hemisphere remains in darkness than the Northern Hemisphere. So a person living at Repulse Bay, Canada, north of the Arctic Circle will experience 24 hours of daylight at the June solstice. On the same day, someone who lives in New York City will have a longer period of daylight than darkness. However, someone who lives in Buenos Aires, Argentina, will experience a longer period of darkness than daylight on that day of the year. On this day of the year is the winter solstice for the Southern Hemisphere. Thus, June 21 is the day with the longest amount of sunlight, with the most sun angle of the year in the Northern Hemisphere, and the day with the least amount of sunlight, with the shortest sun angles of the year, in the Southern Hemisphere. The latitude where at noon the sun is directly above is also known as the sun’s declination.