What is the definition of lightyear?
89663
A light year (or light-year, or lightyear), abbreviated ly, is the distance light travels in one year: about 9.461  × 1015 metres (9.461 petametres), or about 5.879 × 1012 (nearly six trillion) miles. 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). Since the speed of light in a vacuum is exactly 299,792,458 m/s (670,616,629 mph) by the definition of metre, one light year is exactly equal to 9,460,730,472,580,800 m (5,878,625,373,184 mi).\n\nThe 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.\n\nA light year is also equal to about 63,241.077 astronomical units (AU). For a list of lengths on the order of one light year.\n\nUnits 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.\n\n\nMiscellaneous facts\nIt takes 8.3 minutes for light to travel from the Sun to the Earth (a distance of 1.58 × 10-5 light years). \nThe 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. \nThe nearest known star (other than the Sun), Proxima Centauri is 4.22 light years away. \nThe center of our galaxy, the Milky Way, is about 28,000 light years away. The Galaxy is about 100,000 light years across. \nThe Triangulum Galaxy (M33), at a bit under 2.6 million light years away, is the most distant object visible to the naked eye. \nThe nearest large galaxy cluster, the Virgo Cluster, is about 60 million light years away. \nThe 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. \nOne gigaparsec is equal to approximately 3.26 billion light years.
787354
Yes, we're seeing what happened to/on that planet 50,000 years ago. Light years are a measure of distance, not time; one light year is the distance that light travels in one year. Therefore, the light we're seeing from that certain planet left that planet 50,000 years ago. It's like looking back in time.
415548
light travels at 186,000 miles per second, the earth is 25,000 miles around....\n\n25000/186000= 0.1344 seconds
212152
In photometry, luminous flux or luminous power is the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to represent the sensitivity of the human eye.
426747
The speed of light is a measurement of how fast light travels in a vacuum. The speed of light also known as "c" as in the famous Einstein equation E=mc^2. And its equal to 299,792,458 m/s or in U.S miles per hour is about 670million miles per hour!!!!!!! It would take light coming form the sun only 8 seconds to arrive on earth which is 92million miles away. Now say "WOW!!"
1152305
superluminal light is light that is so huge and bright that it hurts to look at it. Like at night when someone take a picture and the flash is too close to your eye you say "wow! that was superluminal!"
1165431
From the physics point of view, our universe thus far is approximately 15 billion light years and expanding every second. Light year is the distance that light with the speed of nearly 300,000 Km/s travels in one year. This distance equals 9, 500, 000, 000, 000 Km (that light travels each year). Now, imagine how big our universe is!!\n\nAbout the second part, The space-time (space and time are inseparable) make our universe. They are both dynamic and the  fact that universe expands means both the space and the time expand. Now, in what do the space and time and our universe expand? This fact is not like other daily facts in our life, it is not possible to assign a place for space-time so that our universe expand in it. We cannot say there is something outside our universe because it is meaningless. These concepts are complex and require in-depth studies and deliberating.\n\nI hope these would be a little helpful...
603933
The only one of these used is the distance of the Earth to the Sun, which I believe is called a parsec. The more scientific method of measurring distance in outer space is the light year, which is the distance light travels in a year. Even this measure is small and most distances of galaxies are measurred in billions of light years.
259168
Light travels at 670,616,629.4 miles per hour, so you multiply that by the number of hours in 35 years.\n\n35 years x 365 days/year x 24 hours/day x speed of light in miles/hour.\n\nIt's like 205,611,058,574,040 miles.
224869
one light year = 9.4605284 × 10^15 meters \n  (go to google and type meters in one light year in the search box)
246225
Currently, the accepted view is that the universe is approximately 78 billion light-years in size. A light-year is the distance light travels in one year (a large number since light travels about 186,000 miles each second). To determine this, astronomers used the WMAP project. See the links to determine how this was accomplished, but only if you don't mind being confused (it is quite lengthy and quite confusing - even for an astronomer such as myself!).
376769
light years isn't a time, it is a distance \nso it would be 2 light years
493310
Refraction: Deflection from a straight path undergone by a light ray or energy wave in passing obliquely from one medium (as air) into another (as glass) in which its velocity is different.
402996
Light travels at 186,000 miles per second, or 300,000 kilometers per second.
158836
The Milky Way galaxy, our galaxy, is 80-100 thousand light years in diameter, and about 3000 light years thick.\n\nA light year is the distance light travels in one year, so it is a measure of distance and not time.  One light year equals about 5,878,499,810,000 miles.
651920
A unit of time equal to 1/60 of a minute or 1/3600 of an hour. The international definition was originally 1/86400th of a mean solar day in 1900, but is now instead the time required for 9,192,631,770 vibrations of a Cs atom. Since the speed of light Eric Weisstein's World of Physics is defined to be 299,792,458 m s-1, this makes the meter Eric Weisstein's World of Physics a derived unit. A mnemonic for the number of seconds in a year is 1 nanocentury is approximately equal to  seconds (1 y =  s, whereas this approximation gives  s).
1001347
Sorry... 2 different mediums... a quart refers to volume where a lightyear refers to distance... 2 different dimensions of measurement.\n\nI guess a more appropriate question might be how fast can one pour a quart of water at the speed of light.