Click here to launch the GLIMPSE/MIPSGAL Image Viewer

GLIMPSE (Galactic Legacy Infrared Midplane Extraordinaire) is a survey of the inner part of the Milky Way Galaxy in which we reside. The images come from the IRAC instrument on board the Spitzer Space Telescope, one of NASA's four "Great Observatories". The telescope was pointed to 111,000 different positions in the sky and snapshots were taken in four different infrared wavelengths, creating a total of 444,000 images. The MIPSGAL survey followed up using the MIPS instrument with another 400,000 images at three longer infrared wavelengths. These surveys have 100 times the sensitivity and over 10 times the resolution of previous surveys, allowing us to see stars and dusty objects throughout most of the Galaxy for the first time.

From all this data two images have been created that you can explore on this site: the IRAC image, and the IRAC/MIPS image. If printed, each would be about 180 feet long.

 

Why Infrared?

Infrared light can penetrate the dust that obscures much of the galaxy, so infrared telescopes let us see what would otherwise be invisible. They can reveal dust heated by supernovae, or peer inside the stellar nurseries where new stars are being born. Infrared telescopes can also see much farther in to the galaxy: visible light telescopes may only see 5% of the way through our Milky Way, while Spitzer can see all the way in.

 

What about those colors?

The Spitzer instruments can see different parts of the infrared spectrum, in the same way that your eye can see different parts (red, green and blue) of the visible spectrum. We refer to the different parts of the spectrum by their wavelengths, which are measured in microns (millionths of a meter). The IRAC instrument used for the GLIMPSE survey sees four wavelengths at 3.6, 4.5, 5.8, and 8 microns. The MIPS instrument used for the MIPSGAL survey sees 24, and 70 microns.

But none of these wavelengths are visible to us, so scientists map them to visible colors to create images like these. The colors are chosen to highlight different physical processes (and yes, so they'll look nice too!) Here are few examples of what the colors can tell us.

 

• Glowing Signposts

The IRAC 8 micron wavelength is displayed as red in the IRAC image and as green in the IRAC/MIPS image. This wavelength shows emission from chemical compounds called Polycyclic Aromatic Hydrocarbons (PAHs). On Earth, we have PAH's all around us. they're found in car exhaust and soot, for instance. In space these small molecules are excited by strong ultraviolet radiation from massive hot stars, making them light up in the 8 μm band. As a result, the PAH glow becomes a signpost for recent high-mass star formation.

 

• Supernoavae Remnants, Ionized Bubbles, and Shocked Gases

Ionized and shocked gases show up at 4.5 microns, displayed as green in the IRAC image. The ionized gas arises in high-mass star formation regions, and the shocked gas emission arises in supernovae remnants and in very young, massive stars in their earliest stages of star formation. You'll have to zoom in to see these. they're much smaller features than the glowing PAHs.

 

• Hot or Not

In addition to the PAH and shocked gas emissions, all of the wavelengths seen by Spitzer's instruments show thermal emission: infrared light created by an object's temperature. Everything glows in some part of the spectrum: the hotter you are, the shorter the wavelength. The heating element of a stove glows red; a tungsten light bulb glows white. People are relatively cool, and glow in the infrared. In these images, stars that are forming are surrounded by a disk or envelope of gas and dust which heats up and glows. The IRAC/MIPS image highlights the youngest forming stars in red.