Topical item: telescopes capable of resolving earth-like planets around other star systems. According to the current New Scientist, creating a distanced swarm of telescopes in space could create the resolving power to image even quite small features on an alien planet.
While not a near-term prospect, in a few hundred years of progress, why not a a whole bunch of reflectors at the earth-sun Lagrange points L4 and L5? With around 200 million miles separation, you should get a pretty good image. (You might have to wait for the right time of year, for the L4-L5 axis to be orthogonal to the direction to the star system).
Suppose they were hostile. Could we take them out, or could they take us out easily? One weapon the military apparently like is the relativistic impact weapon. If you crank up a projectile to ever closer to the speed of light, its apparent incoming velocity to an observer at the target tends to infinity (the projectile catches up with its own light). Doesn't give much time for defensive action, and the energy delivered goes up by much more than the square of the velocity. Perhaps a combination of laser drive initially and then Orion to really pump the energy up? Terminal guidance might be challenging - from the kinetic weapon's point of view, the target is approaching at speeds which also tend to infinity.
Enough of this bad-taste military SF. I blame the cold weather.