Question: What is studied using the infrared system?
About the article "Astronomy", section "Infrared astronomy".

Candidate passages:
On March 22, 2005, Astronomers using NASA's Spitzer Space Telescope took advantage of this fact to directly capture the infrared light of two previously detected planets orbiting outside our solar system.
Their findings revealed the temperatures and orbits of the planets.
Upcoming Spitzer observations using a variety of infrared wavelengths may provide more information about the planets' winds and atmospheric compositions.
It enabled determination of TrES-1's temperature, which is in excess of 1000 K (1340 °F).
The planet's Bond albedo was found to be 0.31 ± 0.14.
In the infrared panel, the colors reflect what our eyes might see if we could retune them to the invisible, infrared portion of the light spectrum.
The hot star is less bright in infrared light than in visible and appears fainter.
The warm planet peaks in infrared light, so is shown brighter.
Their hues represent relative differences in temperature.
Because the star is hotter than the planet, and because hotter objects give off more blue light than red, the star is depicted in blue, and the planet, red.
The overall look of the planet is inspired by theoretical models of hot, gas giant planets.
These "hot Jupiters" are similar to Jupiter in composition and mass, but are expected to look quite different at such high temperatures. 
An infrared countermeasure (IRCM) is a device designed to protect aircraft from infrared homing ("heat seeking") missiles by confusing the missiles' infrared guidance system so that they will miss their target. 
Infrared cleaning works by collecting an infrared channel from the scan at the same time as the visible colour channels (red, green, and blue).
This is done by using a light source that also produces infrared radiation, and having a fourth row of sensors on the linear CCD sensor.
Photographic film is mostly transparent to infrared radiation (no matter what the visible image contains) but dust and scratches aren't, so they show up in the IR channel.
This information can then be used to automatically remove the appearance of dust and scratches in the visible channels and replace them with something similar to their surroundings.
A major limitation of this technique is that it can only be used on dye-based (color and chromogenic black-and-white) films; the image-forming silver particles in most black-and-white film stocks are opaque to infrared radiation.
Scanner manufacturers usually have their own name attached to this technique.
Kodak developed Digital ICE at their Austin development centre, and is licensed by Epson, Nikon, Microtek and some others.
Canon developed its own FARE (Film Automatic Retouching and Enhancement) system.
LaserSoft Imaging is developing the iSRD Dust and Scratch Removal, on which among others Plustek is relying. 
The Northrop Grumman Guardian is a passive anti-missile countermeasure system designed specifically to protect commercial airliners from shoulder-launched missiles (commonly known as MANPADS), using directed infrared countermeasures (DIRCM) technology. 
In infrared photography, infrared filters are used to capture the near-infrared spectrum.
Digital cameras often use infrared blockers.
Cheaper digital cameras and camera phones have less effective filters and can "see" intense near-infrared, appearing as a bright purple-white color.
This is especially pronounced when taking pictures of subjects near IR-bright areas (such as near a lamp), where the resulting infrared interference can wash out the image.
There is also a technique called 'T-ray' imaging, which is imaging using far-infrared or terahertz radiation.
Lack of bright sources makes terahertz photography more challenging than most other infrared imaging techniques.
Recently T-ray imaging has been of considerable interest due to a number of new developments such as terahertz time-domain spectroscopy.