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NASA Spitzer Space Telescope • Jet Propulsion Laboratory
• California Institute of Technology
• Vision for Space Exploration
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Frame Frame About the Spitzer Space Telescope Frame Frame
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Fast Facts
 
Current Status
 
Spitzer History
 
Spitzer Technology
 
Spitzer Science
 
— Why Infrared?
 
— Science Overview
 
— Planets
 
— Stars
 
— Galaxies
 
— Universe
 
— Glossary
 
Lyman Spitzer, Jr.
 

The Rationale for Infrared Astronomy

The scientific potential of Spitzer is rooted in four basic physical principles that define the importance of infrared investigations for studying astrophysical problems. The infrared region is the part of the electromagnetic spectrum stretching from about 1 micron (near-infrared) to 200 microns (far-infrared). Note that the human eye is sensitive to light between the wavelengths of 0.4 and 0.7 microns.

EM Spectrum
Credit: NASA/JPL/IPAC

Blackbody Radiation Graph
Credit: UCSB/K.Kline

Infrared observations reveal cool states of matter.

Solid bodies in space -- ranging in size from sub-micron-sized interstellar dust grains to giant planets -- have temperatures spanning the range from 3 to 1500 Kelvin (K). Most of the energy radiated by objects in this temperature range lies in the infrared. Infrared observations are therefore of particular importance in studying low-temperature environments such as dusty interstellar clouds where stars are forming and the icy surfaces of planetary satellites and asteroids.


Galactic Center
Credits: (left) Howard McCallon, (right) NASA/2MASS/IPAC

Infrared observations explore the hidden Universe.

Cosmic dust grains effectively obscure parts of the visible Universe and block our view of many critical astronomical environments. This dust becomes transparent in the near-infrared, where observers can probe optically invisible regions such as the center of our Milky Way Galaxy (and other galaxies) and dense clouds where stars and planets may be forming. For many objects including dust-embedded stars, active galactic nuclei, and even entire galaxies -- the visible radiation absorbed by the dust and re-radiated in the infrared accounts for virtually the entire luminosity.


M82
Credit: ESA/ISO, SWS, A.F.M. Moorwood

Infrared observations provide access to many spectral features.

Emission and absorption bands of virtually all molecules and solids lie in the infrared, where they can be used to probe conditions in relatively cool celestial environments. Many atoms and ions have spectral features in the infrared which can be used for diagnostic studies of stellar atmospheres and interstellar gas, exploring regions which are too cool or too dust-enshrouded to be reached with optical observations.


Deep Field
Credit: NASA/HST/R. Williams

Infrared observations probe the early life of the cosmos.

The cosmic redshift that results from the general expansion of the Universe inexorably shifts energy to longer wavelengths in an amount proportional to the object's distance. Because of the finite speed of light, objects at high redshifts are observed as they appeared when the Universe and the objects were much younger. As a result of the expansion of the Universe, most of the optical and ultraviolet radiation emitted from stars, galaxies, and quasars since the beginning of time now lies in the infrared. How and when the first objects in the Universe formed will be learned in large part from infrared observations.


Apart from a few narrow windows at the shorter infrared wavelengths, all of the infrared radiation emitted by the above objects is absorbed by Earth's atmosphere. Hence the need for a space-based infrared observatory with high sensitivity -- Spitzer.



The Spitzer Space Telescope is a NASA mission managed by the Jet Propulsion Laboratory. This website is maintained by the Spitzer Science Center, located on the campus of the California Institute of Technology and part of NASA's Infrared Processing and Analysis Center. Privacy Policy

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