What is the share of stars in total radiation input of Earth? Earth gets its radiation input primarily from Sun, then from reflected sunlight from Moon, and stars. Among these, what is the share of stars (or sources outside solar system) to this total radiation input of Earth. Is it negligible compared to solar radiation? (I am referring to top-of-atmosphere situation.)
It is negligible.  

The amount of energy per square metre per second is called the "flux". The flux of the brightest star in the sky, Sirius, is one ten billionth of the sun. That mean the energy the earth receives from the sun in one second is the same as the energy that it gets from Sirius in about 300 years. And Sirius (at magnitude -1.47) is by far the brightest star. All the others add next to nothing.