The phrase "pale blue dot" refers to Earth, our planet, when seen from far away in space. It reminds us that our home, despite its vastness to us, appears small and insignificant in the grand scale of the universe. Full definition
Simple chemistry shows these gases should not co-exist for long, and yet on Earth they do, offering a clear sign for any watchful alien astronomers that something lives and breathes on this particular pale blue dot. (scientificamerican.com)
When astronomers get their picture of a distant pale blue dot, after all, they will want to know whether they're staring at another Earth. (sciencemag.org)
The name of the Pale Red Dot campaign was inspired by the famous pale blue dot image of the Earth, taken in 1990 by Voyager 1 on its way to interstellar space. (earthsky.org)