Thousands of alien worlds have revealed their presence to astronomers by briefly blotting out a bit of starlight as they slip across their home stars’ faces—a simple consequence of celestial geometry. By observing these transits over the last decade, we’ve learned that planets outnumber stars in the Milky Way—and that the galaxy is stuffed with worlds where the conditions could be right for life to thrive.

Now, astronomers are considering the other side of that twinkling equation.

“Which stars could see us as the aliens, as the transiting planet where the Earth blocks out light from the star?” asks Cornell University’s Lisa Kaltenegger, who worked out an answer to that question in a new