We learn much about the world around us by using our eyes. Think about all of the information you obtain and process by simply looking at the world around you. Our eyes are sophisticated detectors that have biologically evolved to ‘see’ visible (or optical) light. There are, however, many other types of light, or radiation, which we cannot see without the aid of high-technology equipment. The human eye’s sensitivity is just a small sliver from the full range of radiation, called the electromagnetic spectrum. To fully appreciate the beauty and complexity of the world around us, we need to rely on man-made devices to provide a view into the ‘invisible’ world. Physicians use x-rays and computed tomography scans (often referred to as CT scan or ‘cat’ scan) to create full 3D images of the human body for diagnoses and air-traffic controllers use it as radar to safely guide aircraft. These are only a few examples of how the study of invisible ‘light’ has contributed to our world. Infrared (IR) light is primarily thermal radiation, a measure of temperature. To the left is a thermal IR image of a person holding a burning match. In this false color image, the white regions are the hottest, the red depicts warm areas, and the coldest portions appear as blue. Note the contrast between the very hot flame and the relatively cool eyeglasses, which do not emit significant amounts of IR radiation. The image to the right is an infrared view of a cat. In this image, the yellow regions are the warmest and the purple areas are cool. Here you can see that the warmest parts of the cat's head are the ears and the eyes, while the coldest region is the kitty's nose. If you have a cat at home, gently feel his/her ear lobes and note the contrast with the cat's nose! These images give an idea of how different the world around us would appear if we had infrared eyes, and begin to reveal the additional information we could not obtain by simply relying on our eyes. Any object with a temperature above absolute zero (-459.67 degrees Fahrenheit, or -273.15 degrees Celsius, or 0 degrees Kelvin), radiates in the infrared. Even objects that we think of as being very cold, such as an ice cube, emit infrared light!Using What We’ve Learned That WorksMost of what we see with our eyes is the result of indirect (or reflected) radiation, provided by the Sun or by artificial lights. The person sitting across your dinner table is visible because of reflected light provided by another radiation source (typically, artificial lighting). However, if your eyes were capable of seeing infrared radiation, that person would be visible to you even in a completely dark room. Why? Because your dinner companion is presumably alive (!), and hence warm, thereby producing infrared radiation. In general, the warmer that an object becomes, the greater the IR radiation it produces. The development, testing, and improvement of infrared detectors has resulted from a productive collaboration between aerospace and industrial firms (primarily funded by the military) and university researchers (funded primarily through NASA). These research efforts into infrared detector technologies have led to many useful applications, apart from defense and space science purposes. We use infrared technology everyday whenever we ‘click’ the television on, or switch channels using a TV remote control. In computers, infrared light is used to read CD-ROM disks. Cashiers use infrared scanners to read standardized bar codes on products, expediting the check-out process. Infrared technology is also used in car locking systems, home security systems, environmental control systems and hand-held temperature monitors. When used as a diagnostic probe -- such as measuring ocean temperature from orbiting satellites, measuring the heat from a person lost in the nighttime wilderness, or detecting structural weaknesses in electrical and mechanical systems -- infrared light permits us to make measurements remotely and to draw factual conclusions without having to touch the objects being measured. In this web module, we explore some of the common and clever uses of infrared light - in science and art, in industry, and for medical and safety diagnostic studies. Then There is Also the Electromagnetic Spectrum (EMF)Electromagnetic fields are energy waves with frequencies below 300 hertz or cycles per second. The electromagnetic fields we encounter daily come from every day things such as power lines, radar and microwave towers, television and computer screens, motors, fluorescent lights, microwave ovens, cell phones, electric blankets, house wiring and hundreds of other common electrical devices.When we look at the world around us we are seeing visible light waves (or visible radiation). However, there are many other forms of radiation that we cannot see with our eyes. These types include gamma rays, x-rays, ultraviolet, infrared, microwaves and radio waves. Together with visible light, all these types of radiation make up what we call the electromagnetic spectrum - the complete spectrum of radiation. Light (or radiation) is made up of vibrating waves of electrical and magnetic fields. This is where the term electromagnetic radiation comes from. Electromagnetic radiation travels in waves which have different wavelengths, energies and frequencies. Wavelength and Frequency The wavelength is the distance between individual waves (e.g. from one peak to another). The wavelengths of visible light range between 400 to 700 billionths of a meter. But the entire electromagnetic spectrum extends from one billionth of a meter (for gamma rays) to meters (for some radio waves). The frequency is the number of waves which pass a point in space each second. Visible light frequencies range between 430 trillion waves per second (red) and 750 trillion waves per second (violet). The entire electromagnetic spectrum has frequencies between less than 1 billion waves per second (radio) and greater than 3 billion billion waves per second (gamma rays). Light waves are waves of energy and the amount of energy in a wave is proportional to its frequency. Wavelength increases, while frequency and energy decreases as we go from gamma rays to radio waves. All electromagnetic radiation travels at the speed of light (186,000 miles or 300,000,000 meters per second in a vacuum). Objects in space send out electromagnetic radiation at all wavelengths - from gamma rays to radio waves. Each type of radiation (or light) brings us unique information so, to get a complete picture of the Universe, we need to study it in all of its light, using each part of the electromagnetic spectrum! Almost everything we know about the Universe comes from the study of the electromagnetic radiation emitted or reflected by objects in space.