What is the Einstein Observatory

The Einstein Observatory, also known as HEAO-2, was launched in 1978 and over its three years of operation, the observatory made many significant contributions to the field of X-ray astronomy. Light classified as X-rays is characterized by a wavelength between 0.01 and 10 nanometers. X-ray astronomy can be traced back to 1949, when researchers first discovered that the sun emits X-rays. Over the course of the following decades, astronomers began to use X-ray detection devices on rockets and satellites to start to explore the capabilities of observing space through X-rays.

In the 1970’s, NASA launched a series of High Energy Astrophysical Observatories to study both Gamma and X-rays. The second of the three observatories, HEAO-2, was renamed Einstein after its launch on November 12, 1978, and focused its attention specifically on X-ray detection. The observatory contained a high-resolution X-ray telescope, and interestingly, four separate instruments upon which the focus of the telescope could be directed. Among these were a High Resolution Imaging detector and Imaging Proportional Counter.

At its time of launch, a number of aspects of the Einstein Observatory garnered attention from the astronomical community and set it apart from other space-based observatories of the time. First, the observatory carried the largest X-ray telescope at the time. Since then, the Chandra Observatory has become the world’s largest. With this increased capability, the Einstein was able to detect X-ray transmissions from thousands of previously unrecorded locations. Einstein’s imaging detectors were also unparalleled at the time and provided a resolution of only a few arcseconds (about 0.00028 degrees). Combined with a sensitivity hundreds of times greater than any previous X-rays and an impressively wide field of view, the Einstein unlocked possibilities in the realm of X-ray that were not previously obtainable.

At the time of Einstein’s launch, X-ray observation was still largely a mystery, and many researchers predicted that telescopes for this wavelength would only detect large cosmic bodies, such as galaxies, and more exotic, unusual objects, but not stars (similar to how radio observations had behaved). To their delight, astronomers found these predictions to be false, and the Einstein proved that stars of all sizes, ages, and classification emitted detectable X-rays. At a 1981 meeting of the American Astronomical Society, astronomer G.S. Vaiana summarized the nearly universal locating of X-rays among stars. “X-ray stars,” says Vaiana, “come from the entire main sequence, much of the giant branch up to [spectral class] K2 and the supergiant branch to spectral type F8.”

In addition to revealing thousands of new stars and opening astronomers’ eyes to the possibility of X-ray observation, the Einstein was also revolutionary in that it made its findings available to the global community through its Guest Observer Program. This addition aided in the spread and recognition of X-rays as a viable way to view stars. Interestingly, once during Einstein’s period of observation, a group of amateur astronomers reported the outbursting of a star (SS Cyngi) and NASA readjusted the observatory to view the star. X-ray astronomy had truly become a field of universal study. During its three and a half years of operation, the Einstein Observatory revolutionized astronomy by making X-ray observations more precise and far-reaching and by proving that it was a feasible way to study and observe the universe.


“The Einstein Observatory.” NASA. 26 Jun. 2008.

Thomsen, Dietrick E. “X-RAYS OF THE STARS.” Science News 119.18 (02 May 1981): 280-286. Academic Search Premier. EBSCO. Nicholson Library, Anderson, IN. 21 Sep. 2008

“X-Ray Astronomy.” The Columbia Encyclopedia, Sixth Edition. Columbia University Press, New York: 2008.