Information AboutNaked Eye |
| CATEGORIES ABOUT NAKED EYE | |
| observational astronomy | |
| vision | |
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Eye characteristics and everyday life The basic accuracies of human eyes are:
Visual perception allows a person to gain much information about his or her environment:
Naked eye in astronomy Normally the naked eye can see stars with Apparent Magnitude up to +6m; angular resolution of the naked eye is about 1′. However, some people have a sharper vision than that; there is anecdotal evidence that they have seen Uranus and the Galilean Moons Of Jupiter . Theoretically, up to +6m the human eye would see about 2,500 stars in the starlit sky, but in practice the atmospheric Extinction and dust reduce the number to 1500–2000 (in the center of a city only 200–500). Colours can be seen just at bright stars and the planets. Additionally some Star Cluster s can be detected ( Pleiades ), h/χ Persei, M13 in Hercules), and the Andromeda and Orion Nebula . The five planets that can be seen from earth with the naked eye, plus the Sun and the Moon, are called the Seven Lights Of The Earth . Meteor showers are better observed by naked eye than with binoculars — eg. the Perseids ( August 10 –12) or the December Geminids . Some 100 Satellite s per night, the International Space Station or the Milky Way are other popular objects. Space, Geodesy , and Navigation Many other things can be estimated without an instrument. If an arm is stretched, the span of the hand corresponds to an angle of 18–20°. The distance of a person is about 600 meters, if just covered up by the thumb. The Vertical can be estimated to about 2°, and the Pole Star and a protractor gives our geographic Latitude up to 1 degree. The Babylonian s, Maya ns and Ancient Egyptian s measured all the basics of their respective Time and Calendar systems by naked eye:
In a similar matter, star Occultation s by the moon can be observed. By a digital Clock , one gets ca. 0.2 s — which are only 200 meters in the moon's distance of 385,000 km. Small objects and maps Observing 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. 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 pollution If 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 Turbulence s — 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 of 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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