The speed of recession of a galaxy is proportional to its distance.

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

Great Bear is a

$A$ group of bright and faint stars is called

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

Describe the Ptolemaic model for planetary motion.