There's water vapor in the Milky Way, although the total amount is 4,000 times less than in the quasar, because most of the Milky Way’s water is frozen in ice.
How could they possibly know this?
How could they possibly know this?
http://en.wikipedia.org/wiki/Black_body
Just like how a noncontact infrared thermometer works, except you have to use a space-based telescope, due to the water in our atmosphere.