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Infrared |
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Infrared light lies between visible an d microwave portions of electromagnetic spectrum. Infrared light has a range of wavelengths. The longer, far infrared wavelengths are about the size of a pin head and the shorter, near infrared ones are the size of cells, or are microscopic.
Far infrared waves are thermal. The heat that we feel from sunlight or a fire is infrared!!! Infrared light is also used to heat food in restaurants sometimes.
Shorter, near infrared waves are not hot and are the ones used by television's remote control. Any object which has a temperature radiates in the infrared.
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Even objects regarded as very cold emit infrared. When an object is not quite hot enough to radiate visible light, it will emit most of its energy in the infrared. Hot charcoal may not give off light but it does emit infrared radiation as heat.
Humans, at normal body temperature, radiate most strongly in the infrared at a wavelength of about 10 microns. (A micron is the term in astronomy for a micrometer or one millionth of a meter.) Humans may not be able to see infrared light, but did you know that snakes in the pit viper family, like rattlesnakes, have sensory "pits", which are used to image infrared light? Many things besides people and animals emit infrared light - the Earth, the Sun, and far away things like stars and galaxies do also! We can also ask why use infrared to image the Earth? While it is easier to distinguish clouds from land in the visible range, there is more detail in the clouds in the infrared. This is convenient for studying cloud structure. Special sensors, like those on the Landsat 7 satellite, gather data about the amount of infrared light reflected or emitted from the Earth's surface. Other satellites, like the IRAS - Infrared Astronomy Satellite measure the infrared light coming from things like large clouds of dust and gas, stars, and galaxies.
What does the Infrared show us? From looking at an infrared image of a cat, we understand that many things emit infrared light. Many things also reflect infrared light, particularly near infrared light. Near infrared radiation is not related to the temperature of the object being photographed - unless the object is very, very hot. Infrared film sees the object because the Sun (or another light source) shines infrared light on it and it is reflected or absorbed by the object. You could say that this reflecting or absorbing of infrared helps to determine the object's 'color' - its color being a combination of red, green, blue, and infrared! Infrared has other uses also, primarily for scientific and military purposes such as infrared imaging and infrared sensors and nighttime vision devices.
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