In order to truly understand astronomical phenomena, we must observe at a wide range of wavelengths. To this end, NASA created the Great Observatories program, which consisted of four space-borne observatories:
- Compton Gamma Ray Observatory (CGRO)
- Chandra X-ray Observatory
- Hubble Space Telescope
- Spitzer Space Telescope
The program was designed so that the operations phases of each of these missions overlapped, allowing astronomers to make contemporaneous observations of an object at multiple wavelengths. The Compton Gamma Ray Observatory launched on April 5, 1991 and was designed to detect high energy gamma rays. The Chandra X-Ray Observatory was deployed in July 1999 and filled in the X-ray portion of the electromagnetic spectrum. The Hubble Space Telescope was deployed in 1990 and repaired to achieve full capability in 1993. It operates at ultraviolet, visual, and near-infrared wavelengths. Finally, the Spitzer Space Telescope was launched on August 25, 2003 and covers the thermal infrared wavelength range not available from the ground due to the Earth’s atmosphere. Together, these four missions covered the bulk of the electromagnetic spectrum completely.
Today, three of these observatories are still operational. The Compton Gamma Ray Observatory re-entered Earth’s atmosphere on June 4, 2000. But, the other three observatories continue to do great research to this date including taking some phenomenal images of Kepler’s Supernova Remnant.