Matches in DBpedia 2016-04 for { <http://wikidata.dbpedia.org/resource/Q818557> ?p ?o }
- Q818557 subject Q6306516.
- Q818557 subject Q7166429.
- Q818557 abstract "Observational astronomy is a division of the astronomical science that is concerned with recording data, in contrast with theoretical astrophysics, which is mainly concerned with finding out the measurable implications of physical models. It is the practice of observing celestial objects by using telescopes and other astronomical apparatus.As a science, the study of astronomy is somewhat hindered in that direct experiments with the properties of the distant universe are not possible. However, this is partly compensated by the fact that astronomers have a vast number of visible examples of stellar phenomena that can be examined. This allows for observational data to be plotted on graphs, and general trends recorded. Nearby examples of specific phenomena, such as variable stars, can then be used to infer the behavior of more distant representatives. Those distant yardsticks can then be employed to measure other phenomena in that neighborhood, including the distance to a galaxy.Galileo Galilei turned a telescope to the heavens and recorded what he saw. Since that time, observational astronomy has made steady advances with each improvement in telescope technology.A traditional division of observational astronomy is given by the region of the electromagnetic spectrum observed: Optical astronomy is the part of astronomy that uses optical components (mirrors, lenses and solid-state detectors) to observe light from near infrared to near ultraviolet wavelengths. Visible-light astronomy (using wavelengths that can be detected with the eyes, about 400 - 700 nm) falls in the middle of this range. Infrared astronomy deals with the detection and analysis of infrared radiation (this typically refers to wavelengths longer than the detection limit of silicon solid-state detectors, about 1 μm wavelength). The most common tool is the reflecting telescope but with a detector sensitive to infrared wavelengths. Space telescopes are used at certain wavelengths where the atmosphere is opaque, or to eliminate noise (thermal radiation from the atmosphere). Radio astronomy detects radiation of millimetre to decametre wavelength. The receivers are similar to those used in radio broadcast transmission but much more sensitive. See also Radio telescopes. High-energy astronomy includes X-ray astronomy, gamma-ray astronomy, and extreme UV astronomy.In addition to using electromagnetic radiation, modern astrophysicists can also make observations using neutrinos, cosmic rays or gravitational waves. Observing a source using multiple methods is known as multi-messenger astronomy.Optical and radio astronomy can be performed with ground-based observatories, because the atmosphere is relatively transparent at the wavelengths being detected. Observatories are usually located at high altitudes so as to minimise the absorption and distortion caused by the Earth's atmosphere. Some wavelengths of infrared light are heavily absorbed by water vapor, so many infrared observatories are located in dry places at high altitude, or in space.The atmosphere is opaque at the wavelengths used by X-ray astronomy, gamma-ray astronomy, UV astronomy and (except for a few wavelength "windows") far infrared astronomy, so observations must be carried out mostly from balloons or space observatories. Powerful gamma rays can, however be detected by the large air showers they produce, and the study of cosmic rays is a rapidly expanding branch of astronomy.For much of the history of observational astronomy, almost all observation was performed in the visual spectrum with optical telescopes. While the Earth's atmosphere is relatively transparent in this portion of the electromagnetic spectrum, most telescope work is still dependent on seeing conditions and air transparency, and is generally restricted to the night time. The seeing conditions depend on the turbulence and thermal variations in the air. Locations that are frequently cloudy or suffer from atmospheric turbulence limit the resolution of observations. Likewise the presence of the full Moon can brighten up the sky with scattered light, hindering observation of faint objects.For observation purposes, the optimal location for an optical telescope is undoubtedly in outer space. There the telescope can make observations without being affected by the atmosphere. However, at present it remains costly to lift telescopes into orbit. Thus the next best locations are certain mountain peaks that have a high number of cloudless days and generally possess good atmospheric conditions (with good seeing conditions). The peaks of the islands of Mauna Kea, Hawaii and La Palma possess these properties, as to a lesser extent do inland sites such as Llano de Chajnantor, Paranal, Cerro Tololo and La Silla in Chile. These observatory locations have attracted an assemblage of powerful telescopes, totalling many billion US dollars of investment.The darkness of the night sky is an important factor in optical astronomy. With the size of cities and human populated areas ever expanding, the amount of artificial light at night has also increased. These artificial lights produce a diffuse background illumination that makes observation of faint astronomical features very difficult without special filters. In a few locations such as the state of Arizona and in the United Kingdom, this has led to campaigns for the reduction of light pollution. The use of hoods around street lights not only improves the amount of light directed toward the ground, but also helps reduce the light directed toward the sky.Atmospheric effects (astronomical seeing) can severely hinder the resolution of a telescope. Without some means of correcting for the blurring effect of the shifting atmosphere, telescopes larger than about 15–20 cm in aperture can not achieve their theoretical resolution at visible wavelengths. As a result, the primary benefit of using very large telescopes has been the improved light-gathering capability, allowing very faint magnitudes to be observed. However the resolution handicap has begun to be overcome by adaptive optics, speckle imaging and interferometric imaging, as well as the use of space telescopes.Astronomers have a number of observational tools that they can use to make measurements of the heavens. For objects that are relatively close to the Sun and Earth, direct and very precise position measurements can be made against a more distant (and thereby nearly stationary) background. Early observations of this nature were used to develop very precise orbital models of the various planets, and to determine their respective masses and gravitational perturbations. Such measurements led to the discovery of the planets Uranus, Neptune, and (indirectly) Pluto. They also resulted in an erroneous assumption of a fictional planet Vulcan within the orbit of Mercury (but the explanation of the precession of Mercury's orbit by Einstein is considered one of the triumphs of his general relativity theory).".
- Q818557 thumbnail Mayall_Telescope.jpg?width=300.
- Q818557 wikiPageExternalLink lot.astro.utoronto.ca.
- Q818557 wikiPageExternalLink owl.
- Q818557 wikiPageWikiLink Q1.
- Q818557 wikiPageWikiLink Q104225.
- Q818557 wikiPageWikiLink Q104499.
- Q818557 wikiPageWikiLink Q1049389.
- Q818557 wikiPageWikiLink Q1055065.
- Q818557 wikiPageWikiLink Q1056113.
- Q818557 wikiPageWikiLink Q1057006.
- Q818557 wikiPageWikiLink Q105902.
- Q818557 wikiPageWikiLink Q1061971.
- Q818557 wikiPageWikiLink Q1068376.
- Q818557 wikiPageWikiLink Q1069.
- Q818557 wikiPageWikiLink Q1073340.
- Q818557 wikiPageWikiLink Q10914152.
- Q818557 wikiPageWikiLink Q11012.
- Q818557 wikiPageWikiLink Q11210.
- Q818557 wikiPageWikiLink Q11276.
- Q818557 wikiPageWikiLink Q1129343.
- Q818557 wikiPageWikiLink Q1134091.
- Q818557 wikiPageWikiLink Q11388.
- Q818557 wikiPageWikiLink Q11391.
- Q818557 wikiPageWikiLink Q11452.
- Q818557 wikiPageWikiLink Q11466.
- Q818557 wikiPageWikiLink Q11523.
- Q818557 wikiPageWikiLink Q11547.
- Q818557 wikiPageWikiLink Q124313.
- Q818557 wikiPageWikiLink Q12458.
- Q818557 wikiPageWikiLink Q125191.
- Q818557 wikiPageWikiLink Q1316958.
- Q818557 wikiPageWikiLink Q133139.
- Q818557 wikiPageWikiLink Q13890.
- Q818557 wikiPageWikiLink Q1413491.
- Q818557 wikiPageWikiLink Q145.
- Q818557 wikiPageWikiLink Q148578.
- Q818557 wikiPageWikiLink Q1504755.
- Q818557 wikiPageWikiLink Q15605.
- Q818557 wikiPageWikiLink Q1617995.
- Q818557 wikiPageWikiLink Q165074.
- Q818557 wikiPageWikiLink Q165896.
- Q818557 wikiPageWikiLink Q170754.
- Q818557 wikiPageWikiLink Q173431.
- Q818557 wikiPageWikiLink Q1752016.
- Q818557 wikiPageWikiLink Q1801478.
- Q818557 wikiPageWikiLink Q180644.
- Q818557 wikiPageWikiLink Q181505.
- Q818557 wikiPageWikiLink Q18335.
- Q818557 wikiPageWikiLink Q184356.
- Q818557 wikiPageWikiLink Q1852.
- Q818557 wikiPageWikiLink Q187634.
- Q818557 wikiPageWikiLink Q188593.
- Q818557 wikiPageWikiLink Q1886563.
- Q818557 wikiPageWikiLink Q189880.
- Q818557 wikiPageWikiLink Q190035.
- Q818557 wikiPageWikiLink Q190120.
- Q818557 wikiPageWikiLink Q193223.
- Q818557 wikiPageWikiLink Q193521.
- Q818557 wikiPageWikiLink Q1961815.
- Q818557 wikiPageWikiLink Q2.
- Q818557 wikiPageWikiLink Q2126.
- Q818557 wikiPageWikiLink Q213636.
- Q818557 wikiPageWikiLink Q216778.
- Q818557 wikiPageWikiLink Q216817.
- Q818557 wikiPageWikiLink Q21994628.
- Q818557 wikiPageWikiLink Q221392.
- Q818557 wikiPageWikiLink Q2344875.
- Q818557 wikiPageWikiLink Q238323.
- Q818557 wikiPageWikiLink Q240105.
- Q818557 wikiPageWikiLink Q2471197.
- Q818557 wikiPageWikiLink Q2513.
- Q818557 wikiPageWikiLink Q25261.
- Q818557 wikiPageWikiLink Q2623243.
- Q818557 wikiPageWikiLink Q271860.
- Q818557 wikiPageWikiLink Q2746952.
- Q818557 wikiPageWikiLink Q280855.
- Q818557 wikiPageWikiLink Q2890543.
- Q818557 wikiPageWikiLink Q298.
- Q818557 wikiPageWikiLink Q307.
- Q818557 wikiPageWikiLink Q308.
- Q818557 wikiPageWikiLink Q3178387.
- Q818557 wikiPageWikiLink Q318.
- Q818557 wikiPageWikiLink Q3198.
- Q818557 wikiPageWikiLink Q323.
- Q818557 wikiPageWikiLink Q3230.
- Q818557 wikiPageWikiLink Q324.
- Q818557 wikiPageWikiLink Q332.
- Q818557 wikiPageWikiLink Q333.
- Q818557 wikiPageWikiLink Q3348306.
- Q818557 wikiPageWikiLink Q336.
- Q818557 wikiPageWikiLink Q339.
- Q818557 wikiPageWikiLink Q3394057.
- Q818557 wikiPageWikiLink Q34777.
- Q818557 wikiPageWikiLink Q35273.
- Q818557 wikiPageWikiLink Q3559.
- Q818557 wikiPageWikiLink Q37547.
- Q818557 wikiPageWikiLink Q3863.