The rate of solar energy incident on a unit area of the Earth is approximately ....... $(kW/m^2)$.

What are the approximate sizes of the observable universe and an atomic nucleus?

When the original mass of a star is greater than $5\, M$ ($M =$ mass of the sun),the death of this star will give rise to:

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 tail of the comet is due to

$A$ total solar eclipse is observed from the Earth. At the same time,an observer on the Moon views the Earth. She is most likely to see ($E$ denotes the Earth):