Question

An astronomer sees a star that is very far away but still very bright. What can she conclude about the star?
Answer

The star must be very large.

The star must be very small.

The star must be moving away from Earth.

The star must be moving closer to Earth.

Answer 1

Its given star is far away, and its bright.
By using the concept of doppler shift we can find if its moving away or moving far.
Since it is far, the light we must be getting now should be really old. So the age of the star is huge. It means its one of the primitive stars. So it might be BIG.

Astronomy is my hobby so i cant tel i am right confidently.

Answer 2

Hm so it is A?

Answer 3

It is A, but not for that reason..... Doppler shift changes the apparent wavelength of the light in such a way that an observer can calculate the star's relative velocity with respect to the earth. This has nothing to do whatsoever with the "age" of the light, nor the age of the star itself. If a star is known to be very far away but still very bright, then that implies that the star is a very intense light source, and intuitively one might guess that this means that the star is very large. While it is more complicated, and the type of star is an important factor, from the answer choices given A is the best.