Infrared astronomy

Infrared astronomy is a specialized branch of astronomy. It focuses on observing and analyzing objects in space using infrared radiation. This radiation has wavelengths ranging from 0.75 to 300 micrometers. This specific range sits between visible light and submillimeter waves.

By studying this light, astronomers can see features of the universe that are invisible to the naked eye. This includes seeing through cosmic dust and observing extremely distant objects.

To understand how this works, we must look at how heat and light interact. Many celestial objects emit thermal energy. This energy is released as infrared radiation. Because of this, infrared telescopes must be kept extremely cold. They often use coolants like liquid nitrogen to stay chilled. If the telescope itself were warm, its own heat would create "noise." This noise would be much stronger than the faint signals from space.

Detectors like HgCdTe arrays are used to capture this light. These arrays work well for wavelengths between 0.6 and 5 micrometers.

Infrared light can be divided into several distinct regions. The near-infrared region has wavelengths just longer than visible light. Because it behaves similarly to visible light, it is often included in the "optical" spectrum. Many optical telescopes, such as those at Keck Observatory, can also see in this range. The mid-infrared covers different wavelengths used by dedicated instruments. Finally, the far-infrared extends all the way to submillimeter wavelengths. Telescopes like the James Clerk Maxwell Telescope observe these much longer waves.

The history of this field began with a famous experiment. In 1800, William Herschel discovered infrared radiation. He used a prism to split sunlight into different colors. He placed thermometers in the light to measure temperature changes. He found the highest temperature increase occurred just beyond the red color. He called these invisible rays "calorific rays."

Later, in 1856, Charles Piazzi Smyth detected radiation from the Moon. Ernest Fox Nichols is also credited with the first detection of a star in infrared. Modern infrared astronomy truly began after the 1960s. This growth followed the success of radio astronomy.

Space missions have provided massive amounts of data. In 1983, the IRAS mission performed an all-sky survey. The European Space Agency launched the Infrared Space Observatory in 1995. Before it ran out of liquid helium in 1998, it discovered water on Saturn and Uranus. NASA launched the Spitzer Space Telescope in 2003. Spitzer discovered the Double Helix Nebula and light from extrasolar planets. Today, the James Webb Space Telescope continues this work from space.

Infrared astronomy is vital for seeing through the obstacles of space. Intergalactic dust can greatly dim the light of distant galaxies. This dust absorbs visible light and re-emits it as infrared light. Because of this, galaxies are actually almost twice as bright as they appear in optical views.

Infrared light also helps us study quasars. These objects move away from Earth, causing a large redshift. This makes them very difficult to see with standard optical telescopes. Infrared tools provide much more information about these distant targets.

Observing from Earth presents a major challenge. Water vapor in our atmosphere absorbs a lot of infrared radiation. To fix this, astronomers build telescopes in very high and dry places. Examples include the Atacama Large Millimeter Array on a high plateau.

Other sites include Mauna Kea and the Antarctic. Some scientists even use airborne observatories like SOFIA to fly above the atmosphere. However, space remains the ideal location. Space telescopes avoid atmospheric blurring and absorption entirely. This allows for the clearest possible view of the cosmos.