Which planet is known as the sister of the Earth?

According to the pulsating theory,the expansion and contraction of the universe repeats after every

The magnitudes of two stars $A$ and $B$ are $2.5$ and $-5$ respectively. The brightness ratio of $\frac{B}{A}$ is

What were the thoughts of the ancient Indian sage and scientist Aryabhatta regarding planetary motion?

The temperature of the Earth without the greenhouse effect would be: (in $^{\circ} C$)

Hubble's law states that the velocity with which a galaxy is moving away from the Earth is proportional to: