Question

(a) Name a star of average brightness.
(b) Why do stars appear as dim points in the night sky?

Answer 1

Hint: We know that the brightness of the star varies with distance from us. Therefore, find the relation between the intensity of brightness and distance from the earth. The stars we see in the night sky are very far away from us.

Complete step by step answer:

(a) Polaris star in our nearest constellation has the average brightness.

(b) To answer this question, we need to understand the terms luminosity and brightness of the stars. The luminosity of the star is the total energy emitted by the star. The brightness of the star is the light output of the star that reaches our eye. This brightness of the star is known as apparent brightness.

When we look into the night sky, we see a wide range of brightness of the star. The brightness of the star depends upon the distance between the star and observer on the earth. We know from the radiation spectra, the energy we receive is inversely proportional to the square of distance from the source. Therefore, if the star is far away from us, the brightness of the star will be very less.

Suppose the luminosity of two stars located at different distances from us is the same. Then, the brightness of the closer star will be greater than the brightness of the farthest star even if they emit the same energy output.

Note:We must note that luminosity and brightness are different. If you stand against a 10 W bulb at a distance 5 m and then again at a distance 10 m. The luminosity of the bulb is the same that is 10 W, but the brightness of the bulb at 10 m will be less as compared to the brightness of the bulb at 5 m distance.