To find ET, look at who’s (maybe) looking at us

map of stars in Milky Way that could see Earth in front of sun

EXTRATERRESTRIAL SURVEILLANCE  Eighty-two known stars (blue dots) within 3,500 light-years of Earth could host advanced civilizations that can see Earth cross in front of the sun.

E. Otwell, C. Crockett; Source: R. Heller and R.E. Pudritz/Astrobiology 2016

As Earth whips around the sun, it casts a shadow into the galaxy.