Who’s watching us?

Earthly astronomers are busy scanning distant star systems for planets. There is one limitation: With the popular transit method, we can only detect planets if they move in front of their star from our point of view and change its brightness. Of course, this limits the selection quite a bit, it is a big coincidence if the orbital plane of an exoplanet is roughly parallel to our viewing direction to the star.

Now you can also ask different questions. Let’s assume that aliens were looking for othe...