Two stars that are in the same constellation:

1. two stars that are in the same constellation: must both be part of the same cluster of stars in space.
2. must both have been discovered at about the same time.
3. may actually be very far away from each other.

Option (3)

Explanation:

A constellation is usually defined as a collection of stars that appears in the sky forming a particular type of shape or pattern. They are located at a very large distance from one another. These constellations are often used in order to locate any astronomical objects in space.

These stars appearing in a constellation generally appears to be closer to one another in the night sky, but they are actually located at about many light years away from one another.  

For example, in the Orion constellation, the stars appearing in the sky are about 25-30 light-years away from one another.

Thus, the correct answer is option (3).