The Universe is continually radiating a wealth of information to Earth, sending signals in a wide spectrum of light. However, not all of these messages reach the ground. Because our planet's atmosphere blocks most radiation coming in from space, humans need to launch telescopes beyond it to get a complete cosmic picture.
Many of the Universe's messages are transmitted in thermal infrared light, which our sky heavily filters. In space, any object that has a temperature above zero Kelvin (-459.67 degrees Fahrenheit, or -273.15 degrees Celsius) radiates in the infrared.
For years, astronomers have tried to place telescopes above the atmosphere, to catch a glimpse of an otherwise hidden infrared universe. This section explores the heritage of infrared astronomy, which culminates with NASA's Spitzer Space Telescope - the most sensitive infrared space observatory ever launched.