Research news
How far away would aliens have to be to detect life on Earth? A scientist has worked out how visible we are in the cosmos
The Search for Extraterrestrial Intelligence (SETI) is interested in finding alien civilisations by detecting signs of their activity.
The use of radio telescopes to listen out for alien broadcasts dates back to the 1960s, but SETI researchers also look for evidence of enormous engineering projects.
See more (external link) 
https://www.skyatnightmagazine.com/space-science/how-far-away-aliens-detect-life-on-earth