The image composite is just one of hundreds that the infrared observatory produced during its 16 years in space.
Five days before NASA’s Spitzer Space Telescope ended its mission on Jan. 30, 2020, scientists used the spacecraft’s infrared camera to take multiple images of a region known as the California Nebula – a fitting target considering the mission’s management and science operations were both based in Southern California at NASA’s Jet Propulsion Laboratory and Caltech. This mosaic is made from those images. It is the final mosaic image taken by Spitzer and one of hundreds the spacecraft captured throughout its lifetime.
Located about 1,000 light-years from Earth, the nebula looks more than a little like the Golden State when viewed by visible-light telescopes: It is long and narrow, bending to the right near the bottom. The visible light comes from gas in the nebula being heated by a nearby, extremely massive star known as Xi Persei, or Menkib. Spitzer’s infrared view reveals a different feature: warm dust, with a consistency similar to soot, that is mixed in with the gas. The dust absorbs visible and ultraviolet light from nearby stars and then re-emits the absorbed energy as infrared light.
The mosaic displays Spitzer’s observations much the way that astronomers would view them: From 2009 to 2020, Spitzer operated two detectors that simultaneously imaged adjacent areas of the sky. The detectors captured different wavelengths of infrared light (referred to by their physical wavelength): 3.6 micrometers (shown in cyan) and 4.5 micrometers (shown in red). Different wavelengths of light can reveal different objects or features. Spitzer would scan the sky, taking multiple pictures in a grid pattern, so that both detectors would image the region at the center of the grid. By combining those images into a mosaic, it was possible to
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