ਪ੍ਰਕਾਸ਼-ਸਾਲ

ਇੱਕ ਪ੍ਰਕਾਸ਼ ਸਾਲ (ਚਿੰਨ੍ਹ: ly) ਲੰਬਾਈ ਮਿਣਨ ਦਾ ਇੱਕ ਸਾਧਨ ਹੈ। ਇੱਕ ਪ੍ਰਕਾਸ਼-ਸਾਲ ਲੱਗ-ਭੱਗ 10 ਅਰਬ ਕਿਲੋਮੀਟਰ ਦੇ ਬਰਾਬਰ ਹੂੰਦਾ ਹੈ। ਇੰਟਰਨੈਸ਼ਨਲ ਐਸਟਰੋਨੋਮੀਕਲ ਯੂਨੀਅਨ ਦੇ ਮੁਤਾਬਕ ਰੋਸ਼ਨੀ ਇੱਕ ਸਾਲ ਵਿੱਚ ਜਿੰਨਾ ਸਫਰ ਤਹਿ ਕਰਦੀ ਹੈ, ਉਸ ਲੰਬਾਈ ਨੂੰ ਇੱਕ ਪ੍ਰਕਾਸ਼-ਸਾਲ ਕਹਿੰਦੇ ਹਨ। ਪ੍ਰਕਾਸ਼-ਸਾਲ ਨੂੰ ਤਾਰਿਆਂ ਦੀ ਦੂਰੀ ਦਾ ਪਤਾ ਕਰਨ ਲਈ ਵਰਤਿਆ ਜਾਂਦਾ ਹੈ।

Numerical value
ਇੱਕ ਪ੍ਰਕਾਸ਼-ਸਾਲ:

 9,460,730,472,580.8 ਕਿਲੋਮੀਟਰ ਹੁੰਦਾ ਹੈ
 ਲੱਗ-ਭੱਗ 5,878,630,000,000 ਮੀਲ ਹੁੰਦਾ ਹੈ

ਉੱਪਰ ਲਿਖੇ ਅੰਕੜੇ ਜੂਲੀਅਨ ਸਾਲ ਦੇ ਹਿਸਾਬ ਨਾਲ ਹਨ, ਜਿਸ ਵਿੱਚ 365.25 ਦਿਨ ਹੁੰਦੇ ਹਨ। ਅਤੇ ਪਹਿਲਾਂ ਹੀ ਤਹਿ ਕੀਤੀ ਰੋਸ਼ਨੀ ਦੀ ਗਤੀ, ਜੋ 299,792,458 ਮੀਲ ਇੱਕ ਸੇਕੰਡ ਵਿੱਚ ਹੈ, ਇਨ੍ਹਾਂ ਦੀ ਵਰਤੋਂ 1984 ਤੋਂ ਹੋ ਰਹੀ ਹੈ।Astronomical Constants  page K6 of the Astronomical Almanac.

+List of orders of magnitude for lengthFactor (ly)ValueItem10−940.4 lyReflected sunlight from the Moon's surface takes 1.2-1.3 seconds to travel the distance to the Earth's surface. (The surface of the moon is roughly 376300 kilometers from the surface of the Earth, on average. 376300 km ÷ 300000 km/s (roughly the speed of light) ≈ 1.25 seconds)10−615.8 lyOne astronomical unit (the distance from the Sun to the Earth). It takes approximately 499 seconds (8.32 minutes) for light to travel this distance.IERS Conventions (2003) , Chapter 1, Table 1-1.10−33.2 lyThe most distant space probe, Voyager 1, was about 14 light-hours away from Earth . It took that space probe 30 years to cover that distance.NASA pressrelease (05-131) 2005-05-24: Voyager Mission Operations Status Report Week Ending March 9, 2007 1001.6 lyThe Oort cloud is approximately two light-years in diameter. Its inner boundary is speculated to be at 50,000 AU, with its outer edge at 100,000 AU2.0 lyMaximum extent of the Sun's gravitational pull (hill sphere/roche sphere, 125,000 AU). Beyond this is true interstellar space4.22 lyThe nearest known star (other than the Sun), Proxima Centauri, is about 4.22 light-years away.NASA: Cosmic Distance Scales - The Nearest Star Proxima Centauri (Gliese 551), Encyclopedia of Astrobiology, Astronomy, and Spaceflight 10326 lyThe center of our galaxy, the Milky Way, is about 8 kiloparsecs away.F. Eisenhauer, et al., "A Geometric Determination of the Distance to the Galactic Center" (pdf, 93KB), Astrophysical Journal 597 (2003) L121-L124McNamara, D. H., et al., "The Distance to the Galactic Center" (pdf, 298KB), The Publications of the Astronomical Society of the Pacific, 112 (2000), pp. 202–216.100 lyThe Milky Way is about 100,000 light-years across. 1062.5 lyThe Andromeda Galaxy is approximately 2.5 megalight-years away.3.14 lyThe Triangulum Galaxy (M33), at 3.14 megalight-years away, is the most distant object visible to the naked eye.59 lyThe nearest large galaxy cluster, the Virgo Cluster, is about 59 megalight-years away.150 - 250 lyThe Great Attractor lies at a distance of somewhere between 150 and 250 megalight-years (the latter being the most recent estimate). 1091.2 lyThe Sloan Great Wall (not to be confused with the Great Wall) has been measured to be approximately one gigalight-year distant.46.5 lyThe comoving distance from the Earth to the edge of the visible universe is about 46.5 gigalight-years in any direction; this is the comoving radius of the observable universe. This is larger than the age of the universe dictated by the cosmic background radiation; see size of the universe: misconceptions for why this is possible.

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