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Ads by Google Your Zodiac Horoscope Insert Your Birthdate & Get Answers about Past-Present and Future. Free AboutAstro.com/horoscope Naked eye   The naked eye Basic accuraciesThe basic accuracies[citation needed] of human eyes are:
Naked eye in astronomyThe visibility of astronomical objects is strongly affected by light pollution. Even a few hundred kilometers away from metropolitan areas where the sky can appear to be very dark, it is still the residual light pollution that sets the limit on the visibility of faint objects. Such conditions are, however, the best observing conditions in reach of most people. Under such "typical" dark sky conditions, the naked eye can see stars with an apparent magnitude up to +6m. Under perfect dark sky conditions where all light pollution is absent, stars as faint as +8m might be visible.[1]The angular resolution of the naked eye is about 1′; however, some people have sharper vision than that. There is anecdotal evidence that people had seen the Galilean moons of Jupiter before telescopes were invented.[2] Of similar magnitude, Uranus and Vesta had most probably been seen but could not be recognized as planets because they appear so small even at maximum brightness that their motion could not be detected. Uranus, when discovered in 1781, was the first planet discovered using technology (a telescope) rather than being spotted by the naked eye. Theoretically, in a typical dark sky, the dark adapted human eye would see the about 5,600 stars brighter than +6m[3] while in perfect dark sky conditions about 45,000 stars brighter than +8m might be visible.[1] In practice, the atmospheric extinction and dust reduce this number somewhat. In the center of a city, where the naked-eye limiting magnitude due to extreme amounts of light pollution can be +4m or less, as few as 200 to 500 stars are visible. Colors can be seen but just at bright stars and the planets, due to the eye's use of rods instead of cones for fainter stars. The visibility of diffuse objects such as star clusters and galaxies is much more strongly affected by light pollution than the visibility of planets and stars. Under typical dark conditions, only a few such objects are visible, such as the Pleiades, h/χ Persei, Andromeda galaxy, the Carina Nebula, the Orion Nebula, Omega Centauri, 47 Tucanae, globular cluster M13 in Hercules. The Triangulum Galaxy (M33) is a difficult averted vision object and only visible at all if it is higher than about 50° in the sky. Under real dark sky conditions, however, M33 is easy to see, even in direct vision. Many other Messier objects are also visible under such conditions.[1] The farthest objects that have been seen by the naked eye are nearby bright galaxies such as Centaurus A,[4] Bode's Galaxy,[5][6][7]Sculptor Galaxy,[7] and Messier 83.[8] Five planets can be recognized as planets from earth with the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. Under typical dark sky conditionsUranus (magnitude +5.8) can be seen as well with averted vision. The Sun and the Moon—the remaining noticeable naked-eye objects of the solar system—are sometimes added to make seven "planets." During daylight only the Moon and Sun are obvious naked eye objects, but in many cases Venus can be spotted in daylight and in rarer cases Jupiter. Close to sunset and sunrise bright stars like Sirius or even Canopus can be spotted with the naked eye as long as one knows exactly where to look. Historically, the zenith of naked-eye astronomy was the work of Tycho Brahe (1546–1601), who built an extensive observatory to make precise measurements of the heavens without any instruments for magnification. In 1610, Galileo Galilei became the first person known to point a telescope towards the sky. He immediately discovered the moons of Jupiter and the phases of Venus, among other things. Meteor showers are better observed by naked eye than with binoculars - the Perseids (10–12 August) or the December Geminids. Some 100 satellites per night, the International Space Station or the Milky Way are other popular visible objects. Many other things can be estimated without an instrument. If an arm is stretched the span of the hand corresponds to an angle of 18 to 20°. The distance of a person, just covered up by the outstretched thumbnail, is about 100 meters. The vertical can be estimated to about 2° and, in the northern hemisphere, the Pole Star and a protractor gives the observer's geographic latitude, up to 1 degree.The Babylonians, Mayans and ancient Egyptians measured all the basics of their respective time and calendar systems by naked eye:
Small objects and mapsObserving a nearby small object without a magnifying glass or a microscope, the usual distance is 20–25 cm. At this close range, 0.05 mm can be seen clearly.[citation needed] The accuracy of a measurement depends on the experience (0.1 to 0.3 mm). The latter figure is the usual position accuracy of faint details in maps, and also of technical plans.Environmental and light pollutionIf the Milky Way is visible, this is an indicator for a clean atmosphere. If we look both at the zenith and toward the horizon, the "blue quality" will degrade depending on the air pollution and dust. The star twinkling is a measure for the air turbulences — e.g. in meteorology and for the "seeing" of astronomy.Light pollution is a significant problem for amateur astronomers but becomes less late at night when many lights are shut off. Air dust can be seen even far away from a city by its "light dome". In winter the snow cover in the city can be estimated without going there. Literature
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Feed a hungry child - donate to school feeding program| ? Mentioned in | ? References in classic literature | ||
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| On the opposite side the enemy could be seen by the naked eye, and from their battery a milk-white cloud arose. You must know that the Marionette, even from his birth, had very small ears, so small indeed that to thenaked eye they could hardly be seen. I could see distinctly the limbs of these vermin with my naked eye, much better than those of a European louse through a microscope, and their snouts with which they rooted like swine. |
