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The last of NASA's Great Observatories is about to lose its cool. When it does, its view of the universe will slowly fade away.

Spitzer Space Telescope was launched five years ago this week. It studies the infrared sky -- the glow produced by stellar nurseries and nursing homes, the incubators for new planets, and other objects with lots of dust.

Infrared is a form of energy that we can't see with our eyes, but that we feel as heat. Most infrared comes from objects that are warm by human standards, but not by astronomical ones -- objects with temperatures of up to a few hundred degrees.

Unfortunately, that includes telescopes. They radiate their own infrared energy, producing a "fog" that overpowers the glow of astronomical objects.

So an infrared telescope must be cooled to frigid temperatures -- the colder, the better. Spitzer, for example, is chilled to near absolute zero by liquid helium. But the helium is running out. When the last of it is used up in a few months, the telescope will slowly warm up, and it will lose part of its vision.

Astronauts can't help Spitzer like they do Hubble Space Telescope. Spitzer trails Earth by a couple of million miles -- far out of a space shuttle's range.

Spitzer won't completely shut down, though. Astronomers are working out a new mission that'll let it continue to observe the universe. But its view will never be the same as during its chilly first five years.

Script by Damond Benningfield, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.