The infrared sky

Abstract The infrared sky from space is the sum of a cosmic signal from galaxies, quasars, and perhaps more exotic sources; and foregrounds from the Milky Way and from the Solar System. At a distance of 1 AU from the Sun, the foreground from interplanetary dust is very bright between 5 and 100 μm, but “very bright” is still several million times fainter than the background produced by ground-based telescopes. In the near infrared 1–2.2 μm range the space infrared sky is a thousand times fainter than the OH nightglow from the Earth’s atmosphere. As a result of these advantages, wide-field imaging from space in the infrared can be an incredibly sensitive method to study the Universe.