Astronomy Day (Spring)
"Now the world has gone to bed, Darkness won't engulf my head, I can see by infrared."
~Douglas Adams, "The Hitchhiker's Guide to the Galaxy", 1978
Infrared radiation (IR) is electromagnetic radiation (EMR) with longer wavelengths than those of visible light, and is therefore generally invisible to the human eye. Most of the thermal radiation emitted by objects near room temperature is infrared.
Infrared was discovered in 1800 by astronomer Sir William Herschel, who discovered a type of invisible radiation in the spectrum lower in energy than red light, by means of its effect on a thermometer. Slightly more than half of the total energy from the Sun was eventually found to arrive on Earth in the form of infrared. The balance between absorbed and emitted infrared radiation has a critical effect on Earth's climate.
In 1856, the Astronomer Royal for Scotland, Charles Piazzi Smythe, invented infrared astronomy by climbing Mount Teide on Tenerife and detecting infrared radiation coming from the Moon.
By 1965, astronomers Gerry Neugebauer and Robert Leighton made the first infrared survey of the cosmos. To do so, they used a declassified version of the infrared technology developed by military organisations to build 'night vision' tools. They found ten objects that were only visible at infrared wavelengths, but four years later, the list had grown to thousands.
Infrared radiation is used in industrial, scientific, military, law enforcement, and medical applications. Night-vision devices using active near-infrared illumination allow people or animals to be observed without the observer being detected. Infrared astronomy uses sensor-equipped telescopes to penetrate dusty regions of space such as molecular clouds, detect objects such as planets, and to view highly red-shifted objects from the early days of the universe.
Spurred by the development of tiny, solid-state imaging devices called infrared arrays, infrared astronomy has undergone a revolution. Astronomers can now obtain electronic images of stars too cool to emit much normal light or too heavily enshrouded in gas and dust for normal light to escape. Moreover, with the advent of adaptive optics, infrared images can now be obtained at the diffraction limit of the Keck 10-m telescope thus revealing exquisite detail in these hidden regions. Infrared measurements taken in astronomical surveys have been particularly effective at unveiling previously undiscovered star clusters.
This tartan, by designer Carol A.L. Martin, was designed to illustrate the long wavelengths beyond visible light such as thermal radiation.
For more on the significance of Infrared astronomy, click the star clusters.