Which planet is known as the sister of the Earth?

Venus looks brighter than other stars because

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 $6.48 \times 10^6 m s^{-1}$.

What is the ratio of the maximum mass of the observable universe to the minimum mass of an electron?

Two stars situated at distances of $1$ and $10$ light years respectively from the earth appear to possess the same brightness. The ratio of their real brightness is

The length of the Milky Way is .......... light years.