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Naked eye (also called bare eye) is the practice of engaging in visual perception unaided by a magnifying or light-collecting optical device, 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 events that can be viewed without equipment, such as an astronomical conjunction, the passage of a comet, or a meteor shower. Sky lore and various tests demonstrate an impressive wealth of phenomena that can be seen with the unaided eye. ==Basic accuracies== The basic accuracies of the human eye are: *Quick autofocus from distances of 10 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 milliradians, 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°.〔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.〕 *Faint stars up to +8 magnitude under a perfectly dark sky.〔http://www.skyandtelescope.com/resources/darksky/3304011.html?c=y&page=1〕 *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 his or her 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 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Naked eye」の詳細全文を読む スポンサード リンク
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