You look at Vega, a star of apparent magnitude m=0, with a telescope of diameter d = 6 inches = 15 cm. How many photons enter the telescope each second? Each second, one million photons per second from Vega pass through an area of 1 sq. cm. We need to find the area of this telescope: diameter = 15 cm radius = 7.5 cm area = pi*radius^2 = 177 sq.cm. Therefore, flux = (1,000,000 photons/sec/sq.cm) * (177 sq.cm.) 177,000,000 photons/sec into telescope That's a lot of photons!