Asked by Sam Lee
We have been broadcasting radio signals since the beginning of the 20th century. It is thought that any civilisation with advanced technology within 78 light years of Earth would be able to pick up on this leaked radiation.
Extraterrestrial civilisations might have difficulty making use of any signals they detect. For example, TV signals would be too weak to make images from and even if they could pick up signals, extraterrestrials would not understand human languages.
If these alien civilisations launched an array of optical telescopes into space, they might be able detect the presence of ozone in our planet’s atmosphere. This might indicate to extraterrestrials that life forms are present on Earth and they are not alone.
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