Even if one side is far more advanced, for the chances of #FirstContact to be maximised there needs to be #cooperative game play. This means both need to choose a #signal the other side may know about, even if they aren't as advanced.

A pretty simple signal is the #transit signal that occurs when a #planet passes directly in front of its #HostStar as seen by a distant observer. The #NASA #Kepker mission found thousands of #exoplanets this way (9/n)