[Encyclios]

Infrared astronomy from earth

The beginnings of astronomical investigation in the infrared can be traced back to S.P. Langley (1881) with the invention of the bolometer. In 1922 decisive improvements were introduced by the use, due to E. Pettit and S.B. Nicholson, of the thermocouple. In the forties, G.P. Kuiper adopted lead sulfide cells for the detectors to be sent to high altitudes, aboard balloons; detectors of which G. Neugebauer and B. Leighton, ten years later, will be the first. Leighton, ten years later, improved the performance with cooling, managing to compile a first catalog of 5612 sources (the Two Micron Survey).

The modern sensors, cooled with nitrogen and liquid helium at a few Kelvin, are ten thousand times more sensitive than their ancestors, and are able to work up to 20 µm. Mounted on rockets, balloons and airplanes (e.g. KAO, Kuiper Airborne Observatory, an aircraft equipped with a 90 cm aperture telescope), during the seventies they already allowed the scanning of about nine tenths of the sky. In this technological phase, we should not forget the TIRGO, a telescope of Italian design installed on the top of the Gornergrat, in Swiss territory.

At the end of the 20th century and at the beginning of the 21st century, the awareness of the importance of infrared astronomy has assumed such general and unconditional connotations that the scientific community has done its best to realize and propose new and increasingly sophisticated designs. For the ground survey, it is worth mentioning the installation on Mauna Kea – over 4000 m high – of 4 powerful structures: the British UKIRT telescope with a 3.8 m mirror; the NASA IRTF telescope, with a 3 m mirror; the twin KECK telescopes, with multiple mirrors for a 10 m aperture. For its part, NASA has built, as a replacement for the Kuiper airborne observatory, a second generation airborne observing facility, SOFIA (Stratospheric Observatory For Infrared Astronomy), to explore the sky over the full range of infrared frequencies thanks to its giant 2.5 m eye and the availability of a vast array of receptors.