We have the knowledge, but not the means
Finding out that we're not alone, stumbling uppon tracks of a different intelligent civilization - these are one of the many space researcher goals. But noticing a spaceship rushing towars us on a telescope is not likely to happen. So, researchers turn to simpler criterions. No water - no life. By that I mean that searching for other life-forms starts from finding habitable planets - not too close to it's star, yet not too far. You won't see space-people through a telescope. In fact, you'll barely see the planet, but there is a way to find out if it has water on it.
To better understand other planets, we have to look upon our own. Water reflects light and we see it best if the object with water is crescent. So to find out whether there is water on the surface of an another planet, scientists have to observe it for several weeks, in order to find out how the planet reflects light. If it's brightest when it's at crescent phase, there is water and we may have found a potential planet for life to evolve on.
Quite a simple process, isn't it? Well, the only problem is that we don't have a telescope able to find distant watery planets. Researchers hope that one will be released in to space in the following decades.