We use the electromagnetic spectrum every day it’s the microwave you use to heat your food and the cell phones you use to text! Those are part of the Electromagnetic Spectrum. The light that our eyes can see is also part of the electromagnetic spectrum. This visible part of the electromagnetic spectrum consists of the colors that we see in a rainbow – from reds and oranges, through blues and purples!! The electromagnetic spectrum has 7 parts to it, radio waves, microwaves, infrared waves, visible light, ultra violet, x-rays, and gamma waves.
Radio waves~ are the electromagnetic waves with the wave length longer than 1mm, it is used for communication. Radio waves also have the longest wavelengths in the electromagnetic spectrum. These waves can be longer than a football field or as short as a football. Radio waves do more than just bring music to your radio. They also carry signals for your television and cellular phones. Because radio waves are larger than optical waves, radio telescopes work differently than telescopes that we use for visible > light (optical telescopes).
Radio telescopes are dishes made out of conducting metal that reflect radio waves to a focus point. Because the wavelengths of radio light are so large, a radio telescope must be physically larger than an optical telescope to be able to make images of comparable clarity. For example, the Parkes radio telescope, which has a dish 64 meters wide, cannot give us any clearer an image than a small backyard telescope! In order to make better and more clear (or higher resolution) radio images, radio astronomers often combine several smaller telescopes, or receiving dishes, into an array.
Together, the dishes can act as one large telescope whose size equals the total area occupied by the array. Microwaves~ are radio waves with wave lengths between 1m and 1mm. Microwaves have wavelengths that can be measured in centimeters! The longer microwaves, those closer to a foot in length, are the waves which heat our food in a microwave oven. Microwaves are good for transmitting information from one place to another because microwave energy can penetrate haze, light rain and snow, clouds, and smoke. Shorter microwaves are used in remote sensing.
These microwaves are used for radar like the Doppler radar used in weather forecasts. Microwaves, used for radar, are just a few inches long. Radar is an acronym for “radio detection and ranging”. Radar was developed to detect objects and determine their range (or position) by transmitting short bursts of microwaves. The strength and origin of “echoes” received from objects that were hit by the microwaves is then recorded. Because radar senses electromagnetic waves that are a reflection of an active transmission, radar is considered an active remote sensing system.
Passive remote sensing refers to the sensing of electromagnetic waves which did not originate from the satellite or sensor itself. The sensor is just a passive observer. Infrared~ is resistance of an object to change in its motion. Infrared light lies between the visible and microwave portions of the electromagnetic spectrum. Infrared light has a range of wavelengths, just like visible light has wavelengths that range from red light to violet. “Near infrared” light is closest in wavelength to visible light and “far infrared” is closer to the microwave region of the electromagnetic spectrum.
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. Visible light~ the only electromagnetic waves we can see. Visible light waves are the only electromagnetic waves we can see. We see these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light. When white light shines through a prism, the white light is broken apart into the colors of the visible light spectrum.
Water vapor in the atmosphere can also break apart wavelengths creating a rainbow. Each Cone in our eyes are receivers for these tiny visible light waves. The Sun is a natural source for visible light waves and our eyes see the reflection of this sunlight off the objects around us. The color of an object that we see is the color of light reflected. All other colors are absorbed. Light bulbs are another source of visible light waves. or in a rainbow corresponds to a different wavelength of electromagnetic spectrum. Ultraviolet~ frequency of an object to a change in its motion.
Ultraviolet (UV) light has shorter wavelengths than visible light. Though these waves are invisible to the human eye, some insects, like bumblebees, can see them! Scientists have divided the ultraviolet part of the spectrum into three regions: the near ultraviolet, the far ultraviolet, and the extreme ultraviolet. The three regions are distinguished by how energetic the ultraviolet radiation is, and by the “wavelength” of the ultraviolet light, which is related to energy. The near ultraviolet, abbreviated NUV, is the light closest to optical or visible light.
The extreme ultraviolet, abbreviated EUV, is the ultraviolet light closest to X-rays, and is the most energetic of the three types. The far ultraviolet, abbreviated FUV, lies between the near and extreme ultraviolet regions. It is the least explored of the three regions. Our Sun emits light at all the different wavelengths in electromagnetic spectrum, but it is ultraviolet waves that are responsible for causing our sunburns. To the left is an image of the Sun taken at an Extreme Ultraviolet wavelength – 171 Angstroms to be exact. (An Angstrom is a unit length equal to 10-10 meters. This image was taken by a satellite named SOHO and it shows what the Sun looked like on April 24, 2000.
Though some ultraviolet waves from the Sun penetrate Earth’s atmosphere, most of them are blocked from entering by various gases like Ozone. Some days, more ultraviolet waves get through our atmosphere. Scientists have developed a UV index to help people protect themselves from these harmful ultraviolet waves. X-rays~ the 2nd highest frequency wave and 2nd shortest in the electromagnetic spectrum. As the wavelengths of light decrease, they increase in energy.
X-rays have smaller wavelengths and therefore higher energy than ultraviolet waves. We usually talk about X-rays in terms of their energy rather than wavelength. This is partially because X-rays have very small wavelengths. It is also because X-ray light tends to act more like a particle than a wave. X-ray detectors collect actual photons of X-ray light – which is very different from the radio telescopes that have large dishes designed to focus radio waves! X-rays were first observed and documented in 1895 by Wilhelm Conrad Roentgen, a German scientist who found them quite by accident when experimenting with vacuum tubes.
What would it be like to see X-rays? Well, we wouldn’t be able to see through people’s clothes, no matter what the ads for X-ray glasses tell us! If we could see X-rays, we could see things that either emit X-rays or halt their transmission. Our eyes would be like the X-ray film used in hospitals or dentist’s offices. X-ray film “sees” X-rays, like the ones that travel through your skin. It also sees shadows left by things that the X-rays can’t travel through (like bones or metal). We use satellites with X-ray detectors on them to do X-ray astronomy.
In astronomy, things that emit X-rays (for example, black holes) are like the dentist’s X-ray machine, and the detector on the satellite is like the X-ray film. X-ray detectors collect individual X-rays (photons of X-ray light) and things like the number of photons collected, the energy of the photons collected, or how fast the photons are detected, can tell us things about the object that is emitting them. To the right is an image of a real X-ray detector. This instrument is called the Proportional Counter Array and it is on the Rossi X-ray Timing Explorer (RXTE) satellite.
It looks very different from anything you might see at a dentist’s office! Gamma Rays~ Gamma-rays have the smallest wavelengths and the most energy of any other wave in the electromagnetic spectrum. These waves are generated by radioactive atoms and in nuclear explosions. Gamma-rays can kill living cells, a fact which medicine uses to its advantage, using gamma-rays to kill cancerous cells. Gamma-rays travel to us across vast distances of the universe, only to be absorbed by the Earth’s atmosphere. Different wavelengths of light penetrate the Earth’s atmosphere to different depths.
Instruments aboard high-altitude balloons and satellites like the Compton Observatory provide our only view of the gamma-ray sky. Gamma-rays are the most energetic form of light and are produced by the hottest regions of the universe. They are also produced by such violent events as supernova explosions or the destruction of atoms, and by less dramatic events, such as the decay of radioactive material in space. Things like supernova explosions (the way massive stars die), neutron stars and pulsars, and black holes are all sources of celestial gamma-rays.
Gamma-ray astronomy did not develop until it was possible to get our detectors above all or most of the atmosphere, using balloons or spacecraft. The first gamma-ray telescope, carried into orbit on the Explorer XI satellite in 1961, picked up fewer than 100 cosmic gamma-ray photons! Unlike optical light and X-rays, gamma rays cannot be captured and reflected in mirrors. The high-energy photons would pass right through such a device. Gamma-ray telescopes use a process called Compton scattering, where a gamma-ray strikes an electron and loses energy, similar to a cue ball striking an eight ball. Primary light colors~ Green, Red and Blue.
University/College: University of Chicago
Type of paper: Thesis/Dissertation Chapter
Date: 21 December 2016
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