Why Mid-Infrared?

The MIRI will cover the spectral region 5 to 27 microns (a micron is the term commonly used in astronomy for a micrometer or one millionth of a meter - visible light is at a wavelength of 0.5 microns). It complements the two other JWST instruments, NIRCam and NIRSpec, which work from 0.6 to 5 microns. The infrared spectral range is discussed here.

At their normal body temperature (98.6 degrees Fahrenheit), humans radiate most strongly in the MIRI spectral range, at a wavelength of about 10 microns.  This image at 10 microns (courtesy of the Infrared Processing and Analysis Center at CalTech), shows a man holding up a lighted match!

This image (courtesy of SE-IR Corporation, Goleta, CA) shows a cat in the mid-infrared. The orange areas are the warmest and the white-blue areas are the coldest. The image reveals the regions inside the ears and the eyes, where the blood flow is most intense, raising the body heat.  http://imagers.gsfc.nasa.gov/ems/infrared.html

In the mid-infrared, astronomers can learn about things they can't "see" at other wavelengths, just as illustrated by analogy in these pictures. Examples are the first light, the assembly of galaxies, the formation of stars and planets, the evolution of planetary systems, and the conditions for life.

For more about the infrared, visit the SIRTF Science Center!