One of the most useful applications of the IR spectrum is in sensing and detection. All objects on Earth emit IR radiation in the form of heat. This can be detected by electronic sensors, such as those used in night vision goggles and infrared cameras. A simple example of such a sensor is the bolometer, which consists of a telescope with a temperature-sensitive resistor, or thermistor, at its focal point, according to the University of California, Berkeley UCB.
If a warm body comes into this instrument's field of view, the heat causes a detectable change in the voltage across the thermistor. Night vision cameras use a more sophisticated version of a bolometer. These cameras typically contain charge-coupled device CCD imaging chips that are sensitive to IR light.
The image formed by the CCD can then be reproduced in visible light. These systems can be made small enough to be used in hand-held devices or wearable night-vision goggles. The cameras can also be used for gun sights with or without the addition of an IR laser for targeting. Infrared spectroscopy measures IR emissions from materials at specific wavelengths.
The IR spectrum of a substance will show characteristic dips and peaks as photons particles of light are absorbed or emitted by electrons in molecules as the electrons transition between orbits, or energy levels.
This spectroscopic information can then be used to identify substances and monitor chemical reactions. According to Robert Mayanovic, professor of physics at Missouri State University, infrared spectroscopy, such as Fourier transform infrared FTIR spectroscopy, is highly useful for numerous scientific applications.
People encounter Infrared waves every day; the human eye cannot see it, but humans can detect it as heat. A remote control uses light waves just beyond the visible spectrum of light—infrared light waves—to change channels on your TV.
This region of the spectrum is divided into near-, mid-, and far-infrared. In , William Herschel conducted an experiment measuring the difference in temperature between the colors in the visible spectrum.
He placed thermometers within each color of the visible spectrum. The results showed an increase in temperature from blue to red. When he noticed an even warmer temperature measurement just beyond the red end of the visible spectrum, Herschel had discovered infrared light!
We can sense some infrared energy as heat. Some objects are so hot they also emit visible light—such as a fire does. Other objects, such as humans, are not as hot and only emit only infrared waves. Our eyes cannot see these infrared waves but instruments that can sense infrared energy—such as night-vision goggles or infrared cameras—allow us to "see" the infrared waves emitting from warm objects such as humans and animals.
The temperatures for the images below are in degrees Fahrenheit. Many objects in the universe are too cool and faint to be detected in visible light but can be detected in the infrared. Scientists are beginning to unlock the mysteries of cooler objects across the universe such as planets, cool stars, nebulae, and many more, by studying the infrared waves they emit. The Cassini spacecraft captured this image of Saturn's aurora using infrared waves.
The aurora is shown in blue, and the underlying clouds are shown in red. These aurorae are unique because they can cover the entire pole, whereas aurorae around Earth and Jupiter are typically confined by magnetic fields to rings surrounding the magnetic poles. The large and variable nature of these aurorae indicates that charged particles streaming in from the Sun are experiencing some type of magnetism above Saturn that was previously unexpected.
Infrared waves have longer wavelengths than visible light and can pass through dense regions of gas and dust in space with less scattering and absorption.
Thus, infrared energy can also reveal objects in the universe that cannot be seen in visible light using optical telescopes. The James Webb Space Telescope JWST has three infrared instruments to help study the origins of the universe and the formation of galaxies, stars, and planets.
A pillar composed of gas and dust in the Carina Nebula is illuminated by the glow from nearby massive stars shown below in the visible light image from the Hubble Space Telescope. Intense radiation and fast streams of charged particles from these stars are causing new stars to form within the pillar.
Most of the new stars cannot be seen in the visible-light image left because dense gas clouds block their light. However, when the pillar is viewed using the infrared portion of the spectrum right , it practically disappears, revealing the baby stars behind the column of gas and dust. Infrared light has a range of wavelengths, just like visible light has wavelengths that range from red light to violet. 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. In other words, we experience this type of infrared radiation every day in the form of heat! The heat that we feel from sunlight, a fire, a radiator or a warm sidewalk is infrared. The temperature-sensitive nerve endings in our skin can detect the difference between inside body temperature and outside skin temperature. Shorter, near infrared waves are not hot at all - in fact you cannot even feel them.
These shorter wavelengths are the ones used by your TV's remote control. Humans, at normal body temperature, radiate most strongly in the infrared at a wavelength of about 10 microns. A micron is the term commonly used in astronomy for a micrometer or one millionth of a meter. This image which is courtesy of the Infrared Processing and Analysis Center at CalTech , shows a man holding up a lighted match! Which parts of this image do you think have the warmest temperature? How does the temperature of this man's glasses compare to the temperature of his hand?
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