The Space Place :: How a Telescope Sees Heat

How to See Heat

	The infrared photo album shows a world that is just as real as the one we see with our eyes. So why can't we normally see this world?
Light is a form of energy. The only difference between the light we can see and infrared radiation we can't see is how much energy it carries. Our eyes react only to visible light. Other kinds of light don't even register. We have invented other ways to see these other forms of light. The light we see is just one form of electromagnetic radiation. Except for objects that are absolutely cold and give off no energy at all, all objects give off electromagnetic radiation. The hotter the object, the more radiation it gives off. Stars like our sun give off huge amounts of electromagnetic radiation at all energies. Cool objects (like ice cubes, people, and cups of coffee) give off mostly infrared radiation. We can detect this radiation as heat. In the infrared pictures you can see with our magic lens, the hotter parts appear red and white, while the colder parts are purple and black. Since the infrared camera is quite sensitive to the different amounts of infrared energy being given off by the objects in its view, you can see which are the hotter parts of the scene. Planets, moons, clouds of dust, and clouds of gas in space are very cool compared with stars and galaxies. So, in order to see them very clearly, it is best to look for the infrared radiation they are putting out. Hotter objects, like stars and galaxies, emit most of their energy in the visible, ultraviolet, and x-ray ranges. The Spitzer Space Telescope, launched into orbit around the Sun in 2003, detects the infrared energy coming from cooler objects in space. Most of this energy is blocked by Earth's atmosphere, so cannot be detected by telescopes on the ground. Besides putting the telescope into space to get it above Earth's atmosphere, Spitzer's designers had some other big problems to solve. Even in space, Spitzer is heated from the Sun and produces its own heat from operating the computers and other instruments. The designers wanted to make sure that the infrared radiation Spitzer detects is coming from interesting objects in space and not from the telescope itself. They solved that problem by using liquid helium to cool the telescope. The telescope is so cold that any infrared energy it detects has to be coming from somewhere else.
This cutaway drawing shows Spitzer's cryostat, with its tank of liquid helium, and the telescope mounted above.
Using the Spitzer Space Telescope, scientists can study dusty clouds where stars form and the icy surfaces of asteroids and the moons of other planets. Also, this telescope will help scientists learn what kinds of chemicals are in the clouds of gas between the stars and in the atmospheres of stars. The Spitzer may also help answer some of astronomy's big questions about the very early history of the Universe. the Spitzer Space Telescope is the fourth great space observatory to be launched by NASA. The others are the
	Hubble Space Telescope -- studies the universe in near-infrared, visible, and ultraviolet light.
	Chandra Space Telescope -- studies the universe in X-ray energy.
	Compton Gamma-Ray Observatory -- studied the very high-energy gamma-ray emitting Universe.
Learn more about all the different energies of light and the technologies we use to detect them. Visit the Land of the Magic Windows. Also, test your skill at "reading" infrared images by playing the Infrared Matching Game.