The globular clusters M 3 in Canes Venatici and M 92 in Hercules are also visible with the naked eye under such conditions. The Triangulum Galaxy (M33) is a difficult averted vision object and only visible at all if it is higher than 50° in the sky. These include the Pleiades, h/χ Persei, the Andromeda Galaxy, the Carina Nebula, the Orion Nebula, Omega Centauri, 47 Tucanae, the Ptolemy Cluster Messier 7 near the tail of Scorpius and the globular cluster M13 in Hercules. Under typical dark conditions only a few such objects are visible. The visibility of diffuse objects such as star clusters and galaxies is much more strongly affected by light pollution than is that of planets and stars. Colors can be seen but this is limited by the fact that the eye uses rods instead of cones to view fainter stars. In the center of a city, where the naked-eye limiting magnitude due to extreme amounts of light pollution can be as low as 2 m, as few as 50 stars are visible. In practice, the atmospheric extinction and dust reduces this number somewhat. Theoretically, in a typical dark sky, the dark adapted human eye would see the about 5,600 stars brighter than +6 m while in perfect dark sky conditions about 45,000 stars brighter than +8 m might be visible. Uranus, when discovered in 1781, was the first planet discovered using technology (a telescope) rather than being spotted by the naked eye. Uranus and Vesta had most probably been seen but could not be recognized as planets because they appear so faint even at maximum brightness Uranus's magnitude varies from +5.3 m to +5.9 m, and Vesta's from +5.2 m to +8.5 m (so that it is only visible near its opposition dates). There is anecdotal evidence that people had seen the Galilean moons of Jupiter before telescopes were invented. The angular resolution of the naked eye is about 1 ′ however, some people have sharper vision than that. Under perfect dark sky conditions where all light pollution is absent, stars as faint as +8 m might be visible. Under such 'typical' dark sky conditions, the naked eye can see stars with an apparent magnitude up to +6 m. For most people, these are likely to be the best observing conditions within their reach. Even a few hundred kilometers away from a metropolitan area 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. The visibility of astronomical objects is strongly affected by light pollution. Light pollution dramatically reduces the visibility of stars. luminosities and colors and their changes by time and directionįurther information: Limiting magnitude § In naked-eye visibility A photographic approximation of a naked eye view of the night sky from a small rural town (top) and a metropolitan area (bottom).the vertical ( plumb line) and the slope of plain objects.the distances and 3-dimensional position of things and persons.Visual perception allows a person to gain much information about their surroundings: Unconscious recognizing of movement (that is ' alarm system' and reflexes).Interval estimations (for example at a plan on paper) to 3–5%.Symmetries of 10–20' (3–6 m per 1 km), see the measurements of Tycho Brahe.Photometry (brightness) to ☑0% or 1% of intensity – in a range between night and day of 1:10,000,000,000.Ability to see faint stars up to +8 magnitude under a perfectly dark sky.Field of view (FOV): simultaneous visual perception in an area of about 160° × 175°.Angular resolution: about 1 arcminute, approximately 0.017° or 0.0003 radians, which corresponds to 0.3 m at a 1 km distance.Quick autofocus from distances of 25 cm (young people) to 50 cm (most people 50 years and older) to infinity.Some basic properties of the human eye are: Sky lore and various tests demonstrate an impressive variety of phenomena visible to the unaided eye. In astronomy, the naked eye may be used to observe celestial events and objects visible without equipment, such as conjunctions, passing comets, meteor showers, and the brightest asteroids, including 4 Vesta. Vision corrected to normal acuity using corrective lenses is still considered 'naked'. Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. JSTOR ( August 2012) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.

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