The Spitzer Space Infrared Telescope Facility
The Space Infrared Telescope Facility in a NASA JPL artwork
Fourth of NASA's Great Observatories for Space Astrophysics
Spitzer SIRTF Science Spectrum Resources Great Observatories

Spitzer Infrared Telescope Orbits the Sun
Nebula NGC 7129
Spitzer Space Telescope shows a cluster of 130 bright newborn stars in the rosebud shaped, rose colored nebula NGC 7129, which is some 3,300 lightyears from Earth

Click to enlarge photo

Credit: NASA/JPL-Caltech/Harvard-Smithsonian CfA
The Spitzer Space Telescope is orbiting the Sun on a five-year mission to reveal previously hidden, dusty regions of the Universe as well as cold and distant objects.

Spitzer is the fourth and last of NASA's series of Great Observatories in Space, a program that has included Hubble Space Telescope, Chandra X-ray Observatory and Compton Gamma Ray Observatory.

Before it was launched August 25, 2003, the Spitzer Space Telescope had been known as the Space Infrared Telescope Facility (SIRTF).

Lyman Spitzer. Once in space, SIRTF was renamed Spitzer Space Telescope for Ohio native and astrophysicist Lyman Spitzer, Jr., who lived from 1914-1997.

Spitzer was one of the great scientists of the 20th century. He contributed to human knowledge of astronomy, thermonuclear fusion, stellar dynamics, and plasma physics.

Spitzer was the first to propose placing a large telescope in space. He was the driving force behind development of the Hubble Space Telescope.

About the Spitzer

The Spitzer Space Telescope was lofted to Earth orbit on a Delta rocket from Kennedy Space Center's launch complex 17-B at Cape Canaveral, Florida, on August 25, 2003. It was the 300th spaceflight for the Delta rocket family.

Spitzer (SIRTF) is a 3,000-lb., 0.85-meter, cryogenically-cooled, space telescope operating as an unmanned infrared astronomy observatory in a solar orbit far beyond the Earth and the Moon.

Because most of the infrared radiation arriving at Earth is blocked by our planet's atmosphere and cannot be observed from the ground, astronomers need Spitzer's infrared sensitivity above Earth's atmosphere to record what they call "the Old, the Cold, and the Dirty," meaning the oldest and coldest things most blocked from our vision across the Universe.

Largest Infrared Telescope


Spitzer makes its images by detecting and recording heat coming from objects in deep space across the Universe.

The heat is infrared energy on the electromagnetic spectrum between the wavelengths of 3 and 180 microns.

One micron is one-millionth of a meter.

One meter is 39.37 inches.

Thus, one micron is 0.0000393700 inches.
Spitzer is the largest infrared telescope ever launched into space. The Spitzer satellite carries a 0.85-meter telescope and three cryogenically-cooled science instruments.

The science instruments are very sensitive, allowing astronomers to peer into regions of the Universe hidden from optical telescopes.

Hot dust. Much of deep space is filled with vast, dense clouds of gas and dust which block our view of visible light.

Fortunately, infrared light can penetrate the clouds of dust and gas, allowing us to see into the centers of galaxies and uncover stars and planetary systems forming.

Cool stars. Infrared light also reveals cooler objects across the Universe. Some of which are smaller stars too dim to be seen in visible light, planets around other stars, and giant clouds of molecules. In fact, many organic and inorganic molecules in space are seen best in infrared light.

Protecting the telescope. Because infrared energy is heat, the telescope must be cooled to a temperature near absolute zero to see infrared unobstructed by heat generated by the telescope itself. Absolute zero is a temperature of –459 degrees Fahrenheit or –273 degrees Celsius.

The telescope also must be protected from the heat of the Sun as well as infrared radiated from Earth. Spitzer has a solar shield and is in an unusual Earth-trailing solar orbit, which places the satellite far enough away from the Earth to allow the telescope to cool without using large amounts of cryogen coolant.

Dewar. A dewar is an insulated container used to store liquefied gases. It has a double wall with a vacuum between the walls and silvered surfaces facing the vacuum.

Spitzer's dewar was topped off with 90 gallons of super-cold liquid helium. That's the cryogen that chills the infrared detectors to a temperature near absolute zero, so they can achieve the highest level of sensitivity to the infrared spectrum of light.

Spitzer has sufficient helium to keep it cold and working until about 2008 or 2009. It is so far from Earth that it won't be refueled when the helium runs out.

First Light

Dusty, starry arms of spiral galaxy M81 via the Spitzer Space Telescope (SIRTF)
Spitzer Space Telescope image of the dusty, starry arms of spiral galaxy M81

Credit: NASA JPL

What is the electromagnetic spectrum?
The Spitzer infrared telescopes's first images quickly re-confirmed that celestial objects viewed through ground-based telescopes and the Hubble Space Telescope look quite different when seen in infrared light.

Origins. NASA's Origins Program seeks to answer the questions, "Where did we come from? Are we alone?" The agency describes the Spitzer observatory as a cornerstone of the Origins Program.

The telescope's ability to search out low-temperature objects helps in the search for planetary systems in the making, some of which may have planets like Earth harboring life.

Spitzer's main objectives are:

Comparison With IRAS

An infrared image of Orion (not by SIRTF)
Pre-Spitzer infrared Orion


Learn more about IRAS »»
Unlike the Infrared Astronomical Satellite (IRAS), which swept its view rapidly across the sky, the Spitzer Space Telescope is a true observatory, carrying a variety of focal plane instruments, including: Spitzer's instrument sensitivity is increased by a factor of 100 to 1000 over that of IRAS, and the spatial resolution is at least a factor of 10 times finer than IRAS.

Spitzer Sees Our Galaxy's Twin

Spiral Galaxy NGC-7331
Our Milky Way galaxy looks very much like the spiral galaxy NGC 7331 photographed by NASA's Spitzer Space Telescope.

Click to enlarge NASA poster

Credit: NASA/JPL-Caltech
What does our Milky Way galaxy look like? It probably resembles spiral galaxy NGC 7331 shown in a new Spitzer image.

In the infrared image, the galaxy's swirling arms spin outward from a central bulge of light, which is outlined by a ring of actively forming stars.

NGC 7331 and the Milky Way do not share the same parents, but they have features in common, including number of stars, mass, spiral arm pattern and rate of new-star formation rate.

NGC 7331 is about 50 million lightyears away from Earth in an area of our night sky we refer to as the constellation Pegasus. One lightyear is the distance light travels in a year, about 5.8 trillion miles.

The galaxy was discovered in 1784 by William Herschel, who also discovered infrared light.

The survey. Spitzer observations of NGC 7311 are part of a large science project, known as the Spitzer Infrared Nearby Galaxy Survey. It is a comprehensive study of 75 nearby galaxies using infrared imaging and spectroscopy.

The project combines Spitzer data with data from other telescopes on the ground and in space. The telescopes receive wavelengths ranging from ultraviolet light to radio waves. The result of the project will be a comprehensive map of the chosen galaxies.

False colors. The false color image of of NGC 7311 demonstrates the power of Spitzer's infrared eye to dissect an object into its various parts. It shows the galaxy's arms in brownish red, the central bulge in blue, and a ring of star formation in yellow.

Spitzer's observations revealed the composition of the galaxy: On Earth, polycyclic aromatic hydrocarbons can be found on burnt toast and in automobile exhaust.

The image by Spitzer's infrared array camera is a four-color composite of invisible light, showing in blue the emissions from wavelengths of 3.6 microns, in green the 4.5 micron emissions, in yellow the 5.8 micron emissions, and in red the 8.0 micron emissions. These wavelengths can not be seen by the human eye.

Black hole. Spitzer's infrared spectrograph showed a black hole at the heart of NGC 7331. The core has an unusually high concentration of massive stars. The black hole at the center probably is about the same size as the one lurking at the core of our own Milky Way galaxy.

Whence the light? The infrared light seen in the Spitzer image originates from two very different sources. At shorter wavelengths (3.6 to 4.5 microns), the light comes mainly from stars, particularly ones that are older and cooler than our Sun. This starlight fades at longer wavelengths (5.8 to 8.0 microns), where instead the glow is from clouds of interstellar dust.

The interstellar dust is a variety of carbon-based organic molecules known collectively as polycyclic aromatic hydrocarbons. Wherever these compounds are found, there will also be dust granules and gas, which provide a reservoir of raw materials for future star formation.

The most intriguing feature of the longer-wavelength image is a ring of dust girdling the galaxy center. With a radius of nearly 20,000 lightyears, the ring is invisible at shorter wavelengths, yet has been detected at sub-millimeter and radio wavelengths. It is mostly polycyclic aromatic hydrocarbons. Spitzer measurements suggest that the ring contains enough gas to produce four billion stars like the Sun.

Other galaxies. Three galaxies about 10 times farther away are seen below NGC 7331 in the image. Left to right, they are NGC 7336, NGC 7335 and NGC 7337. The blue dots scattered throughout the images are foreground stars in our Milky Way galaxy. The red dots are galaxies that are farther away.

The Spitzer Infrared Nearby Galaxies Survey project is conducted by a team of 25 scientists from 12 research institutions.

Spitzer management. NASA's Jet Propulsion Lab (JPL) operates the Spitzer Space Telescope for NASA's Office of Space Science, Washington, D.C. The observatory's science data is processed at the Space Infrared Telescope Facility Science Center at California Institute of Technology in Pasadena. JPL is a division of CalTech.

Other institutions on the team are NASA's Goddard Space Flight Center, Ball Aerospace and Technologies Corporation, Lockheed Martin Space System Company, Smithsonian Astrophysical Observatory, Cornell University, and the University of Arizona.
  • Spitzer's infrared spectrograph was built by Cornell University, Ithaca, New York, and Ball Aerospace Corporation, Boulder, Colorado.

  • Spitzer's infrared array camera was developed at Smithsonian Astrophysical Observatory, Cambridge, Massachusetts, and built by NASA Goddard Space Flight Center, Greenbelt, Maryland.

The Great Observatories

NASA's Great Observatories for Space Astrophysics has been a family of four orbiting satellites carrying telescopes designed to study the Universe in both visible light and non-visible forms of radiation.
  • Hubble Space Telescope was launched in 1990 as the first in the series. Hubble observes in visible light, but also has an infrared camera and a spectrometer. It may continue to work in orbit until 2008.

  • Compton Gamma Ray Observatory, launched in 1991, was the second Great Observatory. It was in Earth orbit from 1991-2000.

  • Chandra X-Ray Observatory, launched in 1999, was the third Great Observatory. It was known as the Advanced X-Ray Astrophysics Facility (AXAF) before launch.

  • Spitzer Space Telescope, formerly known as the Space Infrared Telescope Facility, launched in 2003, was the fourth Great Observatory.

  • James Webb Space Telescope will be a large, infrared-optimized space telescope satellite replacing the Great Observatories around 2011.

Learn more about Spitzer and infrared astronomy: