Infrared astronomy
[3] The discovery of infrared radiation is attributed to William Herschel, who performed an experiment in 1800 where he placed a thermometer in sunlight of different colors after it passed through a prism.
[1] He noticed that the temperature increase induced by sunlight was highest outside the visible spectrum, just beyond the red color.
He dubbed this radiation "calorific rays", and went on to show that it could be reflected, transmitted, and absorbed just like visible light.
[1] Efforts were made starting in the 1830s and continuing through the 19th century to detect infrared radiation from other astronomical sources.
Radiation from the Moon was first detected in 1856 by Charles Piazzi Smyth, the Astronomer Royal for Scotland, during an expedition to Tenerife to test his ideas about mountain top astronomy.
[2] The field of infrared astronomy continued to develop slowly in the early 20th century, as Seth Barnes Nicholson and Edison Pettit developed thermopile detectors capable of accurate infrared photometry and sensitive to a few hundreds of stars.
The field was mostly neglected by traditional astronomers until the 1960s, with most scientists who practiced infrared astronomy having actually been trained physicists.
Before this satellite ran out of liquid helium in 1998, it discovered protostars and water in our universe (even on Saturn and Uranus).
Since then, other infrared telescopes helped find new stars that are forming, nebulae, and stellar nurseries.
During May 2008, a group of international infrared astronomers proved that intergalactic dust greatly dims the light of distant galaxies.
Infrared radiation with wavelengths just longer than visible light, known as near-infrared, behaves in a very similar way to visible light, and can be detected using similar solid state devices (because of this, many quasars, stars, and galaxies were discovered).
Many optical telescopes, such as those at Keck Observatory, operate effectively in the near infrared as well as at visible wavelengths.
Indeed, infrared measurements taken by the 2MASS and WISE astronomical surveys have been particularly effective at unveiling previously undiscovered star clusters.
The reason for this is that objects with temperatures of a few hundred kelvins emit most of their thermal energy at infrared wavelengths.
To achieve higher angular resolution, some infrared telescopes are combined to form astronomical interferometers.
For this reason, most infrared telescopes are built in very dry places at high altitude, so that they are above most of the water vapor in the atmosphere.
