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A light-year, symbol ly, is the distance light travels in one year: exactly Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of wavelengths that are studied in the field of optics. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... 9.4607304725808 × 1015 m (about 9.461 pm). 5.878625373183 × 1012 + 849/1397 (nearly six trillion) miles. 63241.077 AU. More specifically, a light year is defined as the distance that a photon would travel, in free space and infinitely distant from any gravitational or magnetic fields, in one Julian year (365.25 days of 86 400 seconds each). metre or meter, see meter (disambiguation) The metre (in the U.S., chiefly meter) is a measure of length, approximately equal to 3. ... A petametre (American spelling: petameter) (symbol: Pm) is a unit of length equal to 1015 metres. ... A mile is any of a number of units of distance, each in the magnitude of 1–10 km. ... The astronomical unit (AU or au or a. ... In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ... Space has been an interest for philosophers and scientists for much of human history, and hence it is difficult to provide an uncontroversial and clear definition outside of specific defined contexts. ... In physics, gravitation or gravity is the tendency of objects with mass to accelerate toward each other. ... Current flowing through a wire produces a magnetic field (B, labeled M here) around the wire. ... In astronomy, a Julian year is a unit of time defined as exactly 365. ... A day (symbol: d) is a unit of time equal to 24 hours. ... Look up second in Wiktionary, the free dictionary. ... The light year is often used to measure distances to stars: a light year is not a unit of time. In astronomy, the preferred unit of measurement for such distances is the parsec which is defined as the distance at which an object will generate one arcsecond of parallax when the observing object moved one astronomical unit perpendicular to the line of sight to the observer. This is equal to approximately 3.26 light years. The parsec is preferred because it can be more easily derived from, and inter-compared with, observational data. However, outside scientific circles, the term light year is more widely used by the general public. A pocket watch. ... Radio telescopes are among many different tools used by astronomers Astronomy (Greek: αστρονομία = άστρον + νόμος, astronomia = astron + nomos, literally, law of the stars) is the science of celestial objects and phenomena that originate outside the Earths atmosphere, such as stars, planets, comets, auroras, galaxies, and the cosmic background radiation. ... The parsec (symbol pc) is a unit of length used in astronomy. ... A second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or 1/3600 of a degree of arc or 1/1296000 ≈ 7. ... Parallax (Greek: παραλλαγή (parallagé) = alteration) is the change of angular position of two stationary points relative to each other as seen by an observer, due to the motion of an observer. ... The astronomical unit (AU or au or a. ... For a list of lengths on the order of one light year, see the article 1 E15 m. To help compare different distances this page lists lengths starting at 1015 m (1,000,000 million km). ... Units related to the light year are the light minute and light second, the distance light travels in a vacuum in one minute and one second, respectively. A light minute is equal to 17 987 547 480 m. Since light travels 299 792 458 m in one second, a light second is 299 792 458 m in length. A light minute (also written light-minute) is a unit of length. ... A light second is a unit of length. ... A minute is a unit of time equal to 1/60th of an hour and to 60 seconds. ... Look up second in Wiktionary, the free dictionary. ... Miscellaneous facts It takes 8.3 minutes for light to travel from the Sun to the Earth (a distance of 1.58 × 10-5 light years). Reflected sunlight from the Moon's surface takes 1.3 seconds to reach Earth. The most distant space probe, Voyager 1, was 13 light hours (only 1.5 × 10-3 light years) away from Earth in September 2004. It took Voyager 27 years to cover that distance. The nearest known star (other than the Sun), Proxima Centauri is 4.22 light years away. The center of our galaxy, the Milky Way, is about 26,000 light years away. The Galaxy is about 100,000 light years across. The Triangulum Galaxy (M33), at a bit under 2.6 million light years away, is the most distant object visible to the naked eye. The nearest large galaxy cluster, the Virgo Cluster, is about 60 million light years away. The particle horizon (observable part) of the universe has a radius of about 46 billion light years, but light from the edge of the observable universe was emitted only 13.7 billion years ago (the age of the universe). The figures differ because distant objects have continued to recede from us due to cosmological expansion (see Hubble's law). One gigaparsec is equal to approximately 3.26 billion light years. The Sun is the star at the center of Earths solar system. ... Earth (often referred to as The Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth in order of size. ... Bulk composition of the moons mantle and crust estimated, weight percent Oxygen 42. ... Earth (often referred to as The Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth in order of size. ... A space probe is an unmanned space mission in which a spacecraft leaves Earths orbit. ... Voyager 1 lifted off with a Titan 3E Centaur A NASA artists rendition of a Voyager spacecraft The Voyager 1 spacecraft is an 815-kilogram unmanned probe of the outer solar system and beyond, launched September 5, 1977, and currently operational. ... 2004 is a leap year starting on Thursday of the Gregorian calendar. ... The Pleiades star cluster A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ... It has been suggested that this article or section be merged into Alpha Ccentauri. ... The Galactic Center is the rotational center of the Milky Way galaxy. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ... Note: This article contains special characters. ... Messier Object 33, the Triangulum Galaxy. ... Table of all 110 Messier objects. ... Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ... A sky field near some of the brighter galaxies in the Virgo cluster. ... The particle horizon in cosmology is the distance from which particles (of positive mass or of zero mass) can have travelled to the observer in the age of the Universe. ... The deepest visible-light image of the cosmos, the Hubble Ultra Deep Field. ... Nothing is certain as to the extent of either the age or size of the universe, but the age of the Universe, according to the Big Bang theory, is defined as the largest possible value of proper time integrated along a timelike curve from the Earth at the present epoch... Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. ... It has been suggested that this article or section be merged into parsec. ... See also Conversion of units Orders of magnitude (length) This article lists conversion factors between a number of units of measurement. ... Categories: | ... External links Listen to this article · (info) This audio file was created from an article revision dated 2005-06-27, and does not reflect subsequent edits to the article. (Audio help) More spoken articles     Conversion Calculator for Units of LENGTH Categories: Spoken articles | Light | Astronomical units of length Image File history File links Light year. ... Image File history File links Sound-icon. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... June 27 is the 178th day of the year (179th in leap years) in the Gregorian calendar, with 187 days remaining. ... Image File history File links Sound-icon. ...

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	Light year - Wikipedia, the free encyclopedia (519 words) More specifically, a light year is defined as the distance that a photon would travel, in free space and infinitely distant from any gravitational or magnetic fields, in one Julian year (365.25 days of 86 400 seconds each). The light year is often used to measure distances to stars: a light year is not a unit of time. Units related to the light year are the light minute and light second, the distance light travels in a vacuum in one minute and one second, respectively. Howstuffworks "What is a light year?" (469 words) That doesn't make much sense because "light year" contains the word "year," which is normally a unit of time. Light travels at 186,000 miles per second (300,000 kilometers per second). A light year is 5,865,696,000,000 miles (9,460,800,000,000 kilometers).
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