What are constellations?

1. Apparent groupings of stars and planets visible on a given evening

2. Groups of galaxies gravitationally bound and close together in the sky

3. Groups of stars gravitationally bound and appearing close together in the sky

4. Groups of stars making an apparent pattern in the celestial sphere

5. Ancient story boards, useless to modern astronomers

Option 4

Explanation:

A constellation can be defined as that region formed by the stars in such a way that the formation by the group of stars in that area appear to seem an imaginary pattern of some mythological creature, animal, god or some inanimate object formed apparently.

Thus in accordance with the above definition a constellation is a group of stars that forms some apparent pattern in the celestial sphere.