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Encyclopedia > Naked eye

The naked eye is a figure of speech referring to human visual perception that is unaided by enhancing equipment, such as a telescope or binoculars. (It, therefore, does not refer to smaller scale aids such as glasses.) The term is often used in astronomy when referring to events that can be viewed by the general public, such as astronomical conjunctions, passage of comets or meteor showers. Sky lore and various tests demonstrate an impressive wealth of phenomena that can be seen with the unaided eye. A figure of speech, sometimes termed a rhetorical, or elocution, is a word or phrase that departs from straightforward, literal language. ... This article or section does not cite its references or sources. ... 50 cm refracting telescope at Nice Observatory. ... Porro-prism binoculars with central focusing Binocular telescopes, or binoculars, (also known as field glasses) are two identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, one to be viewed through each of the users eyes to present the viewer... This article does not cite its references or sources. ... A giant Hubble mosaic of the Crab Nebula, a supernova remnant. ... Conjunction is a term used in positional astronomy and astrology. ... Comet Hale-Bopp Comet McNaught as seen from Swifts Creek, Victoria, Australia on 23 January 2007 A comet is a small body in the solar system that orbits the Sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail â€” both primarily from the effects of... Leonid Meteor Shower A meteor shower, also known as a meteor storm, is a celestial event where a large number of meteors are seen within a very short period. ... A human eye. ...

Contents

Eye characteristics and everyday life

The basic accuracies of human eyes are:

  • Quick autofocus from distances of 10 cm (young people) ... 50 cm (most people 50 years and older) to infinity
  • Angular resolution: 1–2′ (about 0.02°–0.03°), which corresponds to 30–60 cm at a 1 km distance
  • Field of view (FOV): simultaneous visual perception in an area of about 130° × 160°
  • Faint stars up to +6.5 magnitude
  • 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″ (5–10 cm per 1 km) —see the excellent 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)
  • Speed estimation within 5–10%.

Visual perception allows a person to gain much information about his or her environment: Autofocus (or AF) is a feature of some optical systems that allow them to maintain correct focus on a target. ... Angular resolution describes the resolving power of any optical device such as a telescope, a microscope, a camera, or an eye. ... The field of view is the part of the observable world that is seen at any given moment. ... This article is about the astronomical object. ... In science, magnitude refers to the numerical size of something: see orders of magnitude. ... Photometry is the science of measurement of light, in terms of its perceived brightness to the human eye. ... Sphere symmetry group o. ... Tycho Brahe Monument of Tycho Brahe and Johannes Kepler in Prague Tycho Brahe, born Tyge Ottesen Brahe (December 14, 1546 – October 24, 1601), was a Danish nobleman from the region of Scania (in modern-day Sweden), best known today as an early astronomer, though in his lifetime he was also... The term interval is used in the following contexts: cricket mathematics music time This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... This article or section is in need of attention from an expert on the subject. ... An alarm gives an audible or visual warning of a problem or condition. ... Speed is the rate of motion, or equivalently the rate of change of position, many times expressed as distance d moved per unit of time t. ...

    • the distances and 3-dimensional position of things and persons,
    • the speed of the cars on the street
    • the vertical (plumb line) and the slope of plain objects
    • luminosities and colours —and its changes by time and direction
    • ... and other qualities of objects.

Look up position in Wiktionary, the free dictionary. ... A plumb line is a reference line guided by a string or cord weighted at the end with a large weight known as a plumb bob. ...

Naked eye in astronomy

Normally the naked eye can see stars with an 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 people had seen the Galilean moons of Jupiter before telescopes were discovered. Of similar magnitude, Uranus and Vesta had most probably been seen but could not be recognised to orbit the Sun 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. // Headline text HEY!! HOW ARE YOU ALL?? Its nice of you to come read this page. ... Some of Jupiters moons and their highly inclined orbits Jupiter has 63 known natural satellites. ... Atmospheric characteristics Atmospheric pressure 120 kPa Hydrogen 83% Helium 15% Methane 1. ... 4 Vesta (IPA: ) is the second most massive object in the asteroid belt, with a mean diameter of about 530 km (around 330 miles) and an estimated mass 9% the mass of the entire asteroid belt. ... By the mid 20th century humans had achieved a level of thinking mastery sufficient to leave the surface of the planet for the first time and explore space. ... 50 cm refracting telescope at Nice Observatory. ...


Theoretically, at up to +6m the human eye would see about 2,500 stars in the clear sky but, in practice, the atmospheric extinction and dust reduce the number to 1500 to 2000 (in the center of a city as few as 200 to 500). Colours can be seen but just at bright stars and the planets. Additionally, some star clusters can be detected, such as Pleiades, h/χ Persei, M13 in Hercules, and the Andromeda and Orion Nebula. Five planets can be recognised as planets from earth with the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. The Sun and the Moon--the remaining noticeable naked-eye objects of the solar system--are sometimes added to make seven "planets." Extinction is a term used in astronomy to describe the absorption of light from astronomical objects by matter between them and the observer. ... This article or section does not cite its references or sources. ... The Pleiades, also called Open cluster M45, visible from both the northern and southern hemispheres, consists of many bright, hot stars that were all formed at the same time within a large cloud of interstellar dust and gas. ... Messier Object 13, the Great Globular Cluster in Hercules; one of the most prominent and best known globular clusters of the Northern celestial hemisphere. ... M31 in a small telescope The Andromeda Galaxy (IPA: , also known as Messier 31, M31, or NGC 224; older texts often called it the Andromeda Nebula) is a spiral galaxy approximately 2. ... The entire Orion Nebula in visible light Optical images reveal clouds of gas and dust in the Orion Nebula; an infrared image (right) reveals the new stars shining within. ... It has been suggested that Classical Planets be merged into this article or section. ...


Meteor showers are better observed by naked eye than with binoculars—the Perseids (1012 August) or the December Geminids. Some 100 satellites per night, the International Space Station or the Milky Way are other popular visible objects. The Perseids are a prolific meteor shower associated with the comet Swift-Tuttle. ... August 10 is the 222nd day of the year (223rd in leap years) in the Gregorian Calendar. ... August 12 is the 224th day of the year (225th in leap years) in the Gregorian Calendar. ... The Geminids are a meteor shower caused by an object named 3200 Phaethon, which is thought to be an extinct comet. ... An Earth observation satellite, ERS 2 For other uses, see Satellite (disambiguation). ... International Space Station insignia ISS Statistics Crew: 3 As of December 19, 2006 Perigee: 352. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias), sometimes referred to simply as the Galaxy), is a barred spiral galaxy of the Local Group. ...


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 thumb, is about 600 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. It has been suggested that geodetic system be merged into this article or section. ... Table of geography, hydrography, and navigation, from the 1728 Cyclopaedia. ... An object is in a vertical position when it is aligned in an up-down direction, perpendicular to the horizon. ... For other uses of the words Pole star and Polestar see Polestar (disambiguation). ... Latitude, usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator. ...


The Babylonians, Mayans and ancient Egyptians measured all the basics of their respective time and calendar systems by naked eye: Babylonia was an ancient state in Iraq), combining the territories of Sumer and Akkad. ... 74. ... Khafres Pyramid (4th dynasty) and Great Sphinx of Giza (c. ... A pocket watch, a device used to keep time There are two distinct views on the meaning of time. ... A page from the Hindu calendar 1871-72. ...

  • 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—by Mayan astronomers within 5 to 10 minutes for Venus and Mars.

In a similar manner star occultations by the moon can be observed. By using a digital clock one gets around 0.2 s —which represents only 200 meters at the moon's distance of 385,000 km. A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... Look up Month in Wiktionary, the free dictionary. ... Illumination of the Earth by the Sun on the day of equinox, (ignoring twilight). ... The eight planets and three dwarf planets of the Solar System. ... In this July, 1997 still frame captured from video, the bright star Aldebaran has just reappeared on the dark limb of the waning crescent moon in this predawn occultation. ... A clock (from the Latin cloca, bell) is an instrument for measuring time. ...


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. A magnifying glass A magnifying glass is a single convex lens which is used to produce a magnified image of an object. ... A 1915 Bausch and Lomb Optical microscope. ... In science, engineering, industry and statistics, accuracy is the degree of conformity of a measured or calculated quantity to its actual, nominal, or some other reference, value. ...


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 turbulences — e.g. in meteorology and for the "seeing" of astronomy. Layers of Atmosphere (NOAA) Air redirects here. ... Horizon. ... In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic, stochastic property changes. ... Satellite image of Hurricane Hugo with a polar low visible at the top of the image. ... The word seeing can mean more than one thing: In common usage, the word means visual perception In astronomy, seeing is a technical term related to the blurring effects of air turbulence in the atmosphere In the occult seeing refers to the sight or the ability to see auras or...


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. This time exposure photo of New York City shows sky glow, one form of light pollution. ...


Literature

  • Adobe Comp.: ”Photoshop”, program handbook, versions 5/6, Adobe 2002.
  • 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.

Adobe Photoshop is a bitmap graphics editor (with some text and vector graphics capabilities) published by Adobe Systems. ... The Sternenbote is a monthly Astro Journal, edited by the Austrian astronomical Society (Astroverein) in Vienna. ...

External links


  Results from FactBites:
 
Naked eye - Wikipedia, the free encyclopedia (864 words)
The naked eye is a figure of speech referring to human visual perception that is unaided by enhancing equipment, such as a telescope or binoculars.
the human eye would see about 2,500 stars in the clear sky but, in practice, the atmospheric extinction and dust reduce the number to 1500 to 2000 (in the center of a city as few as 200 to 500).
Meteor showers are better observed by naked eye than with binoculars—the Perseids (10–12 August) or the December Geminids.
  More results at FactBites »

 
 

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