A gigahertz is one thousand megahertz. Early radio work began in the kilohertz regime. The technology was easier at the lowest frequencies because those waves are long. Today, radio astronomers work at frequencies ranging from MHz to THz; a teraHertz is a million megahertz. Wavelengths can be smaller than a millimeter. Radio waves are important for astronomy today.
Astronomical objects emit radio waves , and radio telescopes can pick up these signals and study these far-off objects. Radio astronomy has numerous uses today. One major use is that radio telescopes can pick up radio waves emitted by extremely far away objects and translate those waves into stunning photos of galaxies far, far away.
Many professions make use of radio astronomy. For instance, physicists, meteorologists, oceanographers, and astronomers all use radio telescopes to pick up signals and map pictures of things we might not otherwise be able to see. Radio astronomy was discovered in the s by a scientist named Karl Jansky , an engineer who worked for Bell Telephone Labs. By Professor Felix J. Lockman, Ph. With this humble beginning, radio astronomy was born. He is considered one of the founding figures of radio astronomy.
He figured out that radio waves coming from the center of the galaxy were messing up the phone connection and causing the hiss. He — and the phone — had detected radio waves from space [ 1 ]. Jansky opened up a new, invisible universe. You can see a picture of the antenna used by Karl Jansky to detect radio waves from space in Figure 2. He finished the telescope, which was 31 ft across, in and used it to look at the whole sky and see where radio waves came from.
You can see visible light because the visible-light photons travel in small waves, and your eye is small. But because radio waves are big, your eye would need to be big to detect them.
So while regular telescopes are a few inches or feet across, radio telescopes are much larger. The Arecibo Telescope in the jungle in Puerto Rico is almost 1, ft across.
They look like gigantic versions of satellite TV dishes, but they work like regular telescopes. To use a regular telescope, you point it at an object in space. Light from that object then hits a mirror or lens, which bounces that light to another mirror or lens, which then bounces the light again and sends it to your eye or a camera.
The surface — which may be metal with holes in it, called mesh, or solid metal, like aluminum — acts like a mirror for radio waves. This picture shows how strong the radio waves are and where they are coming from in the sky.
When astronomers look for radio waves, they see different objects and events than they see when they look for visible light. Places that seem dark to our eyes, or to regular telescopes, burn bright in radio waves. Places where stars form, for example, are full of dust. That dust blocks the light from getting to us, so the whole area looks like a black blob.
But when astronomer turns radio telescopes to that spot, they can see straight through the dust: they can see a star being born. Stars are born in giant clouds of gas in space. First, that gas clumps together. Then, because of gravity, more and more gas is attracted to the clump. The clump grows bigger and bigger and hotter and hotter.
When it is huge and hot enough, it starts smashing hydrogen atoms, the smallest atoms that exist, together.
When hydrogen atoms crash into each other, they make helium, a slightly bigger atom. Then, this clump of gas becomes an official star. Radio telescopes take pictures of these baby stars [ 3 ]. Radio telescopes show the secrets of the nearest star, too. The light we see from the Sun comes from near the surface, which is about 9,oF.
But above the surface, the temperature reaches ,oF. Radio telescopes help us learn more about these hot parts, which send out radio waves. The planets in our solar system also have radio personalities. Radio telescopes show us the gases that swirl around Uranus and Neptune and how they move around. If we send radio waves toward Mercury, and then catch the radio waves that bounce back using a radio telescope, we can make a map almost as good as Google Earth [ 4 ].
One of them, Grote Reber, an electronics engineer and avid radio armature, had reviewed Jansky's original discovery and speculated that the signals were of thermal origin caused by very hot objects , and as such they should be easier to detect at higher frequencies. Since Jansky's original work was done at 20 MHz about 15 metre wavelength and a beam width of about 25 degrees, Reber wanted to narrow the effective beam width to obtain finer detail.
Reber reasoned that he should build his first receiver and antenna to operate at MHz 10cm wavelength an extraordinary frequency at that time. With his own resources and enthusiasm, Reber built the first parabolic reflector radio telescope. Since this was deemed a private 'extracurricular' activity, Reber received no sponsorship or support. Besides being the first of its kind, it was also a huge structure.
Basically built by a single individual, it was 9. The term 'Radio Telescope' had not been coined at the time, however Reber gets the credit for building the first one.
Although he did not prove his original hypothesis, his work went on to detail the first radio map of the galactic plane and large portions of the sky. Reber published his work "Cosmic Static" in the late 's.
It was the search for static or noise that led to the development of the radio telescope, and it is essentially noise from the universe that the radio telescope detects.
Buried in this roiling confusion is information that is specific in nature to astronomical objects and phenomena. This noise bears witness to the physical characteristics of the universe.
The information is presented as a mixture of signal properties such as frequency, phase, amplitude and in some cases repetitive patterns. Also present is information that can be mathematically assembled into 'radio pictures' of these cosmic objects.
Some signals arrive from finely defined sources that can be, by and large, considered as point sources quasars and pulsars for example. Other sources cover vast areas and can be thought of as wide field objects. These are clouds of dust and gas, star 'nurseries', galaxies and a plethora of other interesting goodies. To obtain information from these sources, the radio telescope must receive not only specific information but also all the 'noise' from these objects and their surroundings then reject what isn't wanted and record the results.
Radio frequency signals of extraterrestrial origin are extremely weak. As an example, if all the signal energy ever received from all the radio telescopes ever built viewing objects other than the sun were combined, there would not be enough total energy to melt a single snowflake.
The radio telescope must first concentrate signals gathered over a wide area and focus them into a small area. This is the same principle on which the reflecting optical telescope operates. The term "radio optics" refers to this similarity. Since the term 'light' really means electromagnetic radiation, all the same basic equations, theories and principles are applicable to radio, infrared or visible light. The big difference is that optical telescopes operate at extremely high frequencies and microscopic wavelengths, while their cousins the radio telescopes work at lower frequencies and longer wavelengths.
Resolution, which can also be expressed as beam width, is a function of the wavelength of the signal and the diameter of the reflector.
At optical frequencies blue-green light , GHz or a wavelength of. The same mirror operating at radio frequencies 30 GHz for example with a wavelength of 1 cm will have a beam width of about 6 degrees. As can be seen, the beam width for the radio telescope is about , times wider, thus yielding lower resolution observations.
0コメント