Figure 6-32: The Entire Sky at Five Wavelength Ranges These five views show the entire sky at visible, radio, infrared, X-ray, and gamma-ray wavelengths. The entire celestial sphere is mapped onto an oval, with the Milky Way stretching horizontally across the center. (a) In the visible view the constellation Orion is at the right, Sagittarius is in the middle, and Cygnus is toward the left. Many of the dark areas along the Milky Way are locations where interstellar dust is sufficiently thick to block visible light. (b) The radio view shows the sky at a wavelength of 21 cm. This wavelength is emitted by hydrogen atoms in interstellar space. The brightest regions (shown in red) are in the plane of the Milky Way, where the hydrogen is most concentrated. (c) This is a mosaic of the images covering the entire sky as observed by the Wide-field Infrared Survey Explorer (WISE). Most of the emission is from dust particles in the plane of the Milky Way that have been warmed by starlight. (d) The image is made by using X-rays, which is indicated by the highlighted X in the wavelength tab. The X-ray map from ROSAT shows about 50,000 X-ray sources whose intensity runs from red for the less intense sources through yellow and blue for the brightest ones. Extremely high temperature gas emits these X-rays. The white regions, which emit strongly at all X-ray wavelengths, are remnants of supernovae. (e) The image is made by using gamma rays, which is indicated by the highlighted G in the wavelength tab. The gamma-ray view from the Compton Gamma Ray Observatory includes all wavelengths less than about 1.2 × 10−5 nm (photon energies greater than 108 eV). The diffuse radiation from the Milky Way is emitted when fast-moving subatomic particles collide with the nuclei of atoms in interstellar gas clouds. The bright spots above and below the Milky Way are distant, extremely energetic galaxies.
(a: Axel Mellinger; b: Max Planck Institute for Radio Astronomy/Science Photo Library/Science Source; c: NASA/JPL-Caltech/UCLA; d: Max Planck Institute for Extraterrestrial Physics/Science Photo Library/Science Source; e: NASA/Science Photo Library/Science Source)