Optical telescopes on the ground have some disadvantages:. Radio telescopes detect radio waves coming from space. Although they are usually very large and expensive, these telescopes have an advantage over optical telescopes. They can be used in bad weather because the radio waves are not blocked by clouds as they pass through the atmosphere. Radio telescopes can also be used in the daytime as well as at night.
X-rays are partly blocked by the Earth's atmosphere and so X-ray telescopes need to be at high altitude or flown in balloons. Since the telescope is set into the ground it cannot be aimed to different parts of the sky and so can only observe the part of the sky that happens to be overhead at a given time.
A group of radio telescopes can be linked together with a computer so that they are all observing the same object Figure below. The computer combines the data, making the group function like one single telescope. When all the dishes are pointed at the same object, they are like a single telescope with a diameter of Scientists have upped their search for extraterrestrial intelligence with the Allen Telescope Array, a string of radio telescopes, located miles north of San Francisco. The atmosphere blocks some radiation in the infrared part of the spectrum and almost all radiation in the ultraviolet and higher frequency ranges.
Furthermore, motion in the atmosphere distorts light. That distortion is why stars twinkle in the night sky. To minimize these problems, many observatories are built on high mountains, where there is less atmosphere above the telescope. Space telescopes can carry instruments to observe objects emitting various types of electromagnetic radiation such as visible, infrared or ultraviolet light; gamma rays; or x-rays.
X-ray telescopes, such as the Chandra X-ray Observatory, use X-ray optics to observe remote objects in the X-ray spectrum. The Hubble was put into orbit by the Space Shuttle Atlantis in Once it was in orbit, scientists discovered that there was a flaw in the shape of the mirror. A servicing mission to the Hubble by the Space Shuttle Endeavor in corrected the problem. Since that time, the Hubble has provided huge amounts of data that have helped to answer many of the biggest questions in astronomy.
It collects data in visible, infrared, and ultraviolet wavelengths. Each of these telescopes specializes in a different part of the electromagnetic spectrum Figure below. The James Webb is scheduled to launch in Hubble Space Telescope: visible, infrared and ultraviolet light; B. Compton Gamma Ray Observatory inactive : gamma ray; C. Spitzer Space Telescope: infrared; D. Chandra X-ray Observatory: X-ray. Humans have been studying the night sky for thousands of years.
Observing the patterns and motions in the sky helped ancient peoples keep track of time Figure below. By understanding annual rhythms, people could know when to plant crops. They also timed many of their religious ceremonies to coincide with events in the heavens. Many archaeologists think that Stonehenge was used to observe the movement of the moon and the sun.
The ancient Greeks made careful observations of the locations of stars in the sky. Greeks also identified constellations , patterns of stars in the sky Figure below.
They associated the constellations with stories and myths from their culture. Stars in the constellation Orion. Constellations help astronomers today identify different regions of the night sky. Ancient astronomers knew a lot about the patterns of stars and the movement of objects in the sky, but they did not know what these objects actually were. That understanding began in the year , when Galileo turned a telescope toward the heavens. With his telescope, Galileo made the following discoveries among others :.
Galileo was the first person known to look at the Moon through a telescope. The mirrors have shallow angles of reflection because X-rays are so short they only reflect at angles almost parallel to the rays themselves.
At steeper mirror angles the rays won't reflect - instead they will penetrate the mirror like a bullet embedding itself in a wall. Right : Illustration of a crystal gamma-ray detector. The electrons expelled by gamma-rays act like a trigger on an alarm, letting the detector know when gamma rays are passing through. Different energy wavelengths interact with matter in different ways. Radio waves will reflect from a metal that X-rays pass right through.
These differences in the interaction between matter and energy have resulted in telescopes designed to only accommodate very specific wavelengths.
Right : A mosaic of different astronomical phenomena at various wavelengths. Phillips says that telescopes designed for different parts of the electromagnetic spectrum often look dramatically unlike one another. With present technology, it is not possible to build one telescope able to efficiently survey the entire electromagnetic spectrum.
Scientists follow established laws of physics in building telescopes, and an all-wave telescope would have to break those laws. Because it is not currently possible to create an all-wave telescope, the next choice is to create a device that uses many telescopes at once. A device containing all the different types of telescopes would necessarily have to be a satellite so that X-rays and gamma rays could be detected.
Left: If an all-wave telescope were made, it would be on the wish list for both professional and amateur observers. On the tree, the planets are represented in order of their distance from the Sun at the top. The Skylab space station in particular is hailed as a good model for conducting multi-wavelength studies in space. The eight telescopes studied the Sun's spectrum from X-ray almost down to infrared, all with very high quality resolution.
Skylab was coordinated with ground-based astronomers as well. The problem in developing this type of technology today, says Weisskopf, is two-fold. Money is the most immediate impediment.
It would cost several billion dollars just to create a high quality combined optical and X-ray telescope. More difficult to tackle is the social mind-set of scientists. Scientists are often trained to specialize; to study only one segment of the electromagnetic spectrum. Hence we have many X-ray astronomers, radio astronomers, and so on, with fewer scientists following a multi-wavelength approach.
Facilities and instruments are built to study only portions of the spectrum, rather than phenomena as a whole. There are no instruments designed to just study globular clusters, for instance. Optical telescopes make use of either lenses or mirrors to focus the incoming optical light waves. A refracting telescope uses lenses.
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