For each of the following questions, make sure you give the name(s) of the star(

Question

For each of the following questions, make sure you give the name(s) of the star(s) and not just a number. a) Which star appears brightest from Earth? ___ b) Why does it appear so bright? c) Of the stars listed, which star is actually producing the most light? ___ a) If the Sun were further away it would be (brighter/fainter/the same brightness). b) If the Sun were further away its luminosity would be (higher/lower/the same). a) Of the stars listed, which star is furthest from us? ___ b) Why does it appear so bright in our sky?

Explanation / Answer

1)

a)

Sirius, also called as the Dog Star or Sirius A, is the brightest star from Earth. It has a visual magnitude of -1.44.

b)

Star’s brightness depends on its magnitude. The smaller the magnitude number, the brighter the star. The visual magnitude of Sirius is -1.44, which is smaller than any other star.

2)

a)

If the sun were further away it would be fainter. The brightness of a source of light is inversely proportional to the square of the distance from the source. This is because the light's brightness is spread out uniformly over the surface of a sphere. At greater distances, the sphere is larger and so the same quantity of light is spread over a larger area. This makes the light source appear fainter as the distance from it increases.

b)

If the sun were further away, its luminosity would be the same. The brightness of a source depends on how far away it happens to be, but the luminosity of a source does not depend on the distance.

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