The number of stars in our solar system is

$A$ galaxy is observed to be moving with a velocity of $8600 \ km \ s^{-1}$. If it is at a distance of $430$ million light-years from us,the Hubble constant and the corresponding age of the universe are respectively:

If a galaxy is at a distance of $430$ million light years from us,what is the Hubble's constant in $km s^{-1}$ per million light years? Its speed is $6.48 \times 10^6 m s^{-1}$.

Which of the following theories is the most satisfactory regarding the origin of the universe?

The faintest stars visible to the naked eye are called:

There are certain types of stars called variable stars which undergo periodic changes in their light output. If such a star quadruples its light output,how much does its magnitude change?