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Course: NASA > Unit 2
Lesson 4: SpectroscopyRadio waves (1888)
Created by NASA.
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How was radio waves discovered?(6 votes)
They were predicted by James Clerk Maxwell. His theory of electromagnetism was published in 1865. His namesake equations were proposed that there was a wave connecting magnetic and electrical fields that has the property of traveling at the speed of light. In 1887, Heinrich Hertz was the first to incontrovertibly prove the existence of radio waves. He did this by building an instrument that could detect VHF (Very High Frequency) and UHF (Ultra High Frequency) radio waves. Today, a hertz is known as a SI unit of frequency; one cycle per second.(8 votes)
Are there any light waves beyond radio waves?(4 votes)
Yes, radio waves are lower in the Electromagnetic Spectrum than visible Light.
If your asking is there any visible light "below" or lower in the Electromagnetic Spectrum than radio waves, the answer would be no. Since the Electromagnetic Spectrum starts at 1 Hz or 1 cycle per second.
A good visualization of the Electromagnetic Spectrum can be seen here:
https://en.wikipedia.org/wiki/Electromagnetic_spectrum
Hope that helps.(5 votes)
How do radiowaves actually work? All of the videos just say it does but someone has to know if we use it.(4 votes)
They are energy waves. When chemical reactions happen inside stars, for instance, the reactions produce energy as well as changing matter. This energy can be light, heat, or even kinetic energy. Radio waves are a form of radiation energy, which is one way that energy can transfer between matter. (The other two are conduction and convection.) This is specifically a form of electromagnetic radiation, meaning that energy is carried through electromagnetism. Radios work by encoding sound on one end into electricity that can be sent to another radio. Then, the other radio converts it to sound again.(2 votes)
- At2:13how can a baseball on the moon fill the entire field of view of an array of radio antenneas(3 votes)
- I'm not too educated on this field (yet), but I believe they are referring to the power of its zoom ability. Like zooming in on a photo taken from the outside of some library, but being able to zoom in through the front yard, through a window, down a hall, and into the pages of an open book on the floor - and reading the words on it.(3 votes)
what are quasars?(1 vote)
They are luminous black holes that emit radio waves.(1 vote)
- How did Karl Jansky discover that objects in space radiated radio waves?(3 votes)
At :14 to :39, it talks about radio waves getting sent out. Wouldn't the radio waves run out of energy and stop going eventually? Would it bump into something? How did the radio wave survive this many years?(2 votes)
Well, if you look at a light spectrum, you can see that radio waves are just another kind of light. We can see stars many billions of light-years away, and so if those were actually radio wave sources, then we would be able to detect the waves. The waves we would be able to detect are bumping into the earth.
So no, the waves wouldn't run out of energy, and yes, they would eventually bump in to enough things that there wouldn't be any wave left; however, the universes' materiel is so long and far in between that it wouldn't hit very many objects.(2 votes)
what is radio astronomy?(2 votes)- what is meant by RF chain?(2 votes)
Why are radio waves used to communicate with spacecraft , orbiters etc like Voyager 1? Why not use something with a higher frequency like x-rays? Wouldn't something with a higher frequency send information farther and faster?
EDIT:
Okay so the earth's atmosphere absorbs high energy waves ... UV+ so they can't be used for earth to space communication. But, why can't we beam radio waves to a satellite close to earth, then have that satellite beam x-rays or other high energy waves to spacecraft further away?(2 votes)
2:13Video transcript
Guglielmo Marconi's first radio transmissions in 1894 have spread into space for over 100 years at the speed of light. They passed Sirius in 1903, Vega in 1919, and Regulus in 1971. That signal has already passed over 1,000 stars. Anyone orbiting one of those stars, with a really good receiver, could detect Marconi's signal and know that we are here. Radio waves are the longest, and contain the least energy, of any electromagnetic wave. While visible light is measured in minute fractions of an inch, radio waves vary from about 19 centimeters, about the length of a water bottle, to waves the length of cars, ships, mountains, all the way up to monstrous waves longer than the diameter of our planet. Heinrich Hertz discovered radio waves in 1888. The first commercial radio station went on the air in Pittsburgh, Pennsylvania, on November 2, 1920. Then in 1932, a major discovery by Karl Jansky at Bell Labs revealed that stars and other objects in space radiated radio waves! Radio astronomy was born. However, scientists need giant antennas to detect weak, long-wavelength, radio waves from space. The enormous Arecibo radio dish antenna measures 305 meters in diameter, over three football fields. Scientists can link the signals from an array of separate radio antennas to focus on tiny slices of distant space. Such arrays act as a single immense collector. This giant New Mexico array uses 27 parabolic dish antennas shaped into a giant "Y" with each arm capable of stretching for 13 miles! Scientists have even spread these linked antennas across the globe. One of the largest stretches from Hawaii to the Virgin Islands and acts like such a powerful telephoto lens that a baseball sitting on the moon would fill its entire field of view. Many of the greatest astronomical discoveries have been made using radio waves. Pulsars, the existence of giant clouds of superheated plasma, which are among the largest objects in the Universe, and even quasars, such as this one over 10 billion light years away, were all discovered using radio waves. Radio waves also provide more local information. Astronomical objects that have a magnetic field usually produce radio waves such as our Sun. Thus, NASA's STEREO satellite is able to monitor bursts of radio waves from the Sun's corona. WAVE sensors on the WIND spacecraft record the radio waves emitted by a planet's ionosphere, such as the bursts from Jupiter whose wavelength measures about fifteen meters. Radio waves fill the space around us to bring entertainment, communications, and key scientific information. We can't hear these radio waves. When you tune your radio to your favorite station, the radio receives these electromagnetic radio waves and then vibrates a speaker to create the sound waves we hear. We may not be able to tap our toes to the cosmic radio transmissions, but we certainly discovered much about our Universe's grand cosmic dance by listening to them. <audio radio sounds from Saturn> our satellites, and other electronics here on Earth. Other NASA instruments monitor the changes in other aspects of the Earth's climate system, such as clouds, aerosol particles, or surface reflectivity, and scientists are examining their many interactons with the energy budget. A portion of solar radiation from the Sun that is just beyond the visible spectrum is referred to as near-infrared. Scientists can study how this radiation reflects off the Earth's surface to understand changes in land cover such as growth of cities or changes in vegetation. Our eyes perceive a leaf as green because wavelengths in the green region of the visible light spectrum are reflected while other visible wavelengths are absorbed. Yet, the chlorophyll and the cell structure of the leaf are also reflecting near-infrared light, light we cannot see. This reflected near-infrared radiation can be sensed by satellites, allowing scientists to study vegetation from space. Using these data, scientists can identify some types of trees, can examine the health of forests, and can even monitor the health of vegetation such as forests infested with pine beetles or crops affected by drought. Studying the emission and reflection of infrared waves helps us to understand the Earth's system and its energy budget. Near-infrared data can also help scientists study land cover such as changes in snow, ice, forests, urbanization, and agriculture. Scientists are beginning to unlock the mysteries of cooler objects across the Universe such as planets, cool stars, nebulae,
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and much more using infrared waves.
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