Light year
From Wikinfo
- There was also a 1988 animated science fiction film named "Light Years".
A light year, abbreviated ly, is the distance light travels in one year: roughly 9.46 � 1012 kilometres (9.46 petametres, or about 5.88 � 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 far away from any gravitational or magnetic fields, in one Julian year (365.25 days of 86400 seconds each). Since the speed of light in a vacuum is exactly 299,792,458 m/s, one light year is exactly equal to 9,460,730,472,580,800 m.
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. 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 light year is also equal to 63,241 astronomical units (AU). For a list of lengths on the order of one light year, see the article 1 E15 m.
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.
Contents |
Miscellaneous facts
- It takes 8.3 minutes for light to travel from the Sun to the Earth (thus, we are about 8.3 light minutes from the Sun).
- The most distant space probe, Voyager 1, was 13 light hours away from Earth in September 2004, less than two tenths of one percent of a light year.
- The nearest known star, Proxima Centauri is 4.22 light years away.
- Our galaxy, the Milky Way, is about 100,000 light years across. This means that it would take at least 100,000 years of cosmic time for any object to cross it; but the proper time experienced by the object might be much smaller than this (time dilation).
- The 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 the cosmological expansion of the universe is not subject to a light-speed limitation. Contrary to popular belief, the universe is not expanding at the speed of light, and is not 13 billion or even 46 billion light years across; it is, in fact, much larger, maybe infinite.
See also
External link
- Conversion Calculator for Units of LENGTH[[cs:Sv?teln� rok]]
[[da:Lys�r]][[es:A�o luz]][[fr:Ann�e lumi�re]][[is:Lj�s�r]][[hu:F�ny�v]][[no:Lys�r]][[sk:Sveteln� rok]][[sv:Ljus�r]][[vi:N?m �nh s�ng]]
References
- Adapted from the Wikipedia article, "Light_year" http://en.wikipedia.org/wiki/Light_year, used under the GNU Free Documentation License
