Question

The sunlight’s intensity that hits the Earth can be treated as approximately constant at the “top” of the Earth’s atmosphere where the intensity is 1.37 kW/m/m. Justify why this is true.

Answer 1

The distance between sun and earth is magnificently huge, for which the sun rays that falls on earths surface can be considered as parallel instead of radial. Now the earths radius is also very large for which if we try to measure something small on earths surface/atmosphere then the surface will tend to act as a flat surface instead of spherical one. Now its clear that if we measure the intensity of parallel rays on a flat surface then it will always remain constant.

Point to be noted:- the sunlight's intensity remains constant only at a particular time. Due to the earths revolution in an elliptical orbit, the intensity changes from time to time.