Naked eye - wikipedia Naked eye For other uses, see Naked eye ( disambiguation ). `` Bare eye '' redirects here. For the bird genus, see Bare - eye. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( August 2012 ) The naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying or light - collecting optical instrument, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered `` naked ''. 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 certain near - Earth asteroids, including 4 Vesta. Sky lore and various tests demonstrate an impressive variety of phenomena visible to the unaided eye. Contents 1 Basic accuracies 2 Naked eye in astronomy 3 Space, geodesy and navigation 4 Small objects and maps 5 Environmental pollution 6 Literature 7 References 8 External links Basic accuracies The basic accuracies of the human eye are : Quick autofocus from distances of 25 cm ( young people ) to 50 cm ( most people 50 years and older ) to infinity. Angular resolution : about 1 arcminute, approximately 0.02 ° or 0.0003 radians, which corresponds to 0.3 m at a 1 km distance. Field of view ( FOV ) : simultaneous visual perception in an area of about 160 ° × 175 °. Faint stars up to + 8 magnitude under a perfectly dark sky. Photometry ( brightness ) to ± 10 % or 1 % of intensity -- in a range between night and day of 1 : 10,000,000,000. Symmetries of 10 -- 20 ' ( 3 -- 6 m per 1 km ), see the measurements of Tycho Brahe and the Egyptians. Interval estimations ( for example at a plan on paper ) to 3 -- 5 %. Unconscious recognizing of movement ( that is `` alarm system '' and reflexes ). Visual perception allows a person to gain much information about their surroundings : the distances and 3 - dimensional position of things and persons the vertical ( plumb line ) and the slope of plain objects luminosities and colors and their changes by time and direction Naked eye in astronomy A photographic approximation of a naked eye view of the night sky from a small rural town ( top ) and a metropolitan area ( bottom ). Light pollution dramatically reduces the visibility of stars. The visibility of astronomical objects is strongly affected by light pollution. 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. For most people, these are likely to be the best observing conditions within their reach. Under such `` typical '' dark sky conditions, the naked eye can see stars with an apparent magnitude up to + 6. Under perfect dark sky conditions where all light pollution is absent, stars as faint as + 8 might be visible. 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. Of similar magnitude, Uranus and Vesta had most probably been seen but could not be recognized as planets because they appear so faint 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 + 6 while in perfect dark sky conditions about 45,000 stars brighter than + 8 might be visible. In practice, the atmospheric extinction and dust reduces this number somewhat. 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, with as few as 50 stars visible. Colors can be seen but this is limited by the fact that the eye uses rods instead of cones to view fainter stars. 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. Under typical dark conditions only a few such objects are visible. 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. The Triangulum Galaxy ( M33 ) is a difficult averted vision object and only visible at all if it is higher than 50 ° in the sky. The globular clusters M 3 in Canes Venatici and M 92 in Hercules are also visible with the naked eye under such conditions. Under really dark sky conditions, however, M33 is easy to see, even in direct vision. Many other Messier objects are also visible under such conditions. The most distant objects that have been seen by the naked eye are nearby bright galaxies such as Centaurus A, Bode 's Galaxy, Sculptor Galaxy, and Messier 83. Five planets can be recognized as planets from Earth with the naked eye : Mercury, Venus, Mars, Jupiter, and Saturn. Under typical dark sky conditions Uranus ( 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 the exact position in which to look. Historically, the zenith of naked - eye astronomy was the work of Tycho Brahe ( 1546 -- 1601 ). He built an extensive observatory to make precise measurements of the heavens without any instruments for magnification. In 1610, Galileo Galilei pointed 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. Such showers include the Perseids ( 10 -- 12 August ) and the December Geminids. Some 100 satellites per night, the International Space Station and the Milky Way are other popular objects visible to the naked eye. 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 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, observing the Pole Star and using a protractor can give the observer 's geographic latitude, up to 1 degree of accuracy. The Babylonians, Mayans, ancient Egyptians, ancient Indians, and Chinese measured all the basics of their respective time and calendar systems by naked eye : the length of a year and a month to ± 0.1 hour or to better than 1 minute ( 0.001 % ) the 24 hours of a day, and the equinoxes the periods of the planets were calculated by Mayan astronomers, to within 5 to 10 minutes accuracy in the case of Venus and Mars. In a similar manner star occultations by the moon can be observed. By using a digital clock an accuracy of 0.2 second is possible. This represents only 200 meters at 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 size of the object depends on the viewing distance. Under normal lighting conditions ( light source ~ 1000 lumens at height 600 -- 700 mm, viewing angle ~ 35 degrees ) the angular size recognized by naked eye will be round 1 arc minute = 1 / 60 degrees = 0.0003 radians. At a viewing distance of 16 '' = ~ 400 mm, which is considered a normal reading distance in the USA, the smallest object resolution will be ~ 0.116 mm. For inspection purposes laboratories use a viewing distance of 200 -- 250 mm, which gives the smallest size of the object recognizable to the naked eye of ~ 0.058 - 0.072 mm ( ~ 55 - 75 micrometers ). The accuracy of a measurement ranges from 0.1 to 0.3 mm and depends on the experience of the observer. The latter figure is the usual positional accuracy of faint details in maps and technical plans. Environmental pollution The Milky Way is visible over the Very Large Telescope, demonstrating clear atmosphere above Paranal Observatory. A clean atmosphere is indicated by the fact that the Milky Way is visible. Comparing the zenith with the horizon, shows how the `` blue quality '' is degraded depending on the amount of air pollution and dust. The twinkling of a star is an indication of the turbulence of the air. This is of importance 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 ''. Literature Davidson, N. : Sky Phenomena : A Guide to Naked Eye Observation of the Heavens. FlorisBooks ( 208p ), ISBN 0 - 86315 - 168 - X, Edinburgh 1993. Gerstbach G. : Auge und Sehen -- der lange Weg zu digitalem Erkennen. Astro Journal Sternenbote, 20p., Vol. 2000 / 8, Vienna 2000. Kahmen H. ( Ed. ) : Geodesy for Geotechnical and Structural Engineering. Proceedings, Eisenstadt 1999. References ^ Jump up to : Yanoff, Myron ; Duker, Jay S. ( 2009 ). Ophthalmology 3rd Edition. MOSBY Elsevier. p. 54. ISBN 0444511415. Jump up ^ Wandell, B. ( 1995 ). `` Foundations of Vision. '' Sinauer, Sunderland, MA as cited in Neurobiology of Attention. ( 2005 ). Eds. Laurent Itti, Geraint Rees, and John K., Tsotos. Chapter 102, Elder, J.H. et al. Elsevier, Inc. Jump up ^ http://www.skyandtelescope.com/resources/darksky/3304011.html?c=y&page=1 ^ Jump up to : John E. Bortle ( February 2001 ). `` The Bortle Dark - Sky Scale ''. Sky & Telescope. Retrieved 2009 - 11 - 18. Jump up ^ Zezong, Xi, `` The Discovery of Jupiter 's Satellite Made by Gan De 2000 years Before Galileo '', Chinese Physics 2 ( 3 ) ( 1982 ) : 664 -- 67. Jump up ^ `` Vmag < 6 ''. SIMBAD Astronomical Database. Retrieved 2009 - 12 - 03. Jump up ^ http://astronomy-mall.com/Adventures.In.Deep.Space/aintno.htm Jump up ^ SEDS, Messier 81 Jump up ^ S.J. O'Meara ( 1998 ). The Messier Objects. Cambridge : Cambridge University. ISBN 0 - 521 - 55332 - 6. ^ Jump up to : http://messier.obspm.fr/xtra/supp/m81naked.txt Jump up ^ Inglis Mike ( 2007 ). `` Galaxies ''. Patrick Moore 's Practical Astronomy Series : 157 -- 189. doi : 10.1007 / 978 - 1 - 84628 - 736 - 7_4. Jump up ^ `` Archived copy ''. Archived from the original on 21 September 2013. Retrieved 12 September 2013. Jump up ^ `` Mars, 2099 ? ''. ESO Picture of the Week. Retrieved 25 June 2012. External links Naked Eye Observing in Astronomy Naked - Eye Stargazing : Learning the Sky and its constellations Naked Eye Navigation, Polynesia Voyages Detection of weak optical signals by the human visual system : Perspectives in Neuroscience and in Quantum Physics The Naked - eye Planets in the Night Sky ( and how to identify them ) Retrieved from `` https://en.wikipedia.org/w/index.php?title=Naked_eye&oldid=833668584 '' Categories : Observational astronomy Vision Hidden categories : Articles needing additional references from August 2012 All articles needing additional references All articles with unsourced statements Articles with unsourced statements from March 2011 Articles with unsourced statements from July 2014 All articles with dead external links Articles with dead external links from January 2018 Articles with permanently dead external links Use dmy dates from November 2010 Talk Contents About Wikipedia Asturianu Català Deutsch Eesti Español Esperanto فارسی Français 한국어 Bahasa Indonesia Italiano Latviešu Lëtzebuergesch Bahasa Melayu Nederlands 日本 語 Norsk ਪੰਜਾਬੀ Plattdüütsch Polski Русский Simple English کوردی Svenska 粵語 中文 18 more Edit links This page was last edited on 1 April 2018, at 21 : 38. 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Question: what is the limit of resolution of the human eye in micrometers
Answer: ~55-75 micrometers; ~55-75 micrometers; ~ 0.116 mm