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

Which planet is known as the sister of the Earth?

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

The hottest planet of the solar system is

$A$ bright star is indicated to have a brightness magnitude of $-5$ compared to a star of brightness zero magnitude. It means that this star,compared to the reference star of zero brightness,is:

The percentage of the Sun's total energy that reaches the Earth's surface is: