## Light year

A light year is known to many of the fantastic novels. Despite the fact that his name is similar to time period of year, a light year measures not time, but distance. This unit is designed to measure huge cosmic distances.

A light year is a unit of length. This is the distance in one year (exactly 365.25 days or 31 557 600 seconds) light travels in a vacuum.

Comparison of light-years from the calendar was used after 1984, prior To that a light year is called the distance traveled by light in one tropical year.

The length of the tropical year is not an accurate value, as its calculation is associated with the angular velocity of the Sun, and for her there is variation. For light-years was taken as the average value.

The difference in calculations between the tropical light year and light year, correlated with the Julian calendar, is 0.02 percent. As well as this unit for high-precision measurements not used, the practical difference between them.

Light year as a unit of length used in scientific popular literature. In astronomy there is another non-si unit for measuring long distances is the parsec. The calculation of a parsec is repelled from the average radius of earth's orbit. 1 parsec is equal to 3,2616 light-years.

## Calculations and distance

Calculate a light year is directly related to the speed of light. For calculations in physics it is usually taken equal to 300 000 000 m/s. the Exact value of the speed of light 299 792 458 m/s. that is 299 792 458 meters is one light second!

The distance to the moon is approximately 384 400 000 m, so the surface of the moon the light beam will reach approximately 1.28 seconds.

Distance from the sun to the Earth 149 600 000 000. Consequently, a ray of sunlight falls on the Earth in a little less than 7 minutes.

So in year 31 557 600 seconds. Multiplying this number by a distance equal to one light second, one light year is 9 460 730 472 580 800 metres.

1 million light years, respectively, will be equal to 9 460 730 472 580 800 000 000 meters.

According to approximate calculations of astronomers, the diameter of our Galaxy is about 100,000 light years. That is within our Galaxy may not be the distances, measured in millions of light years. These numbers are applicable to measure distances between galaxies.

Closest to Earth is the Andromeda galaxy located at a distance of 2.5 million light years.

To date, the largest cosmic distance from Earth, which is possible to measure the distance to the edge of the observable Universe. It is about 45 billion light years.

# Advice 2 : How long is a light year in outer dimension

The term "light year" is found in many scientific articles, popular television shows, books and even the news from the world of science. However, some people believe that a light year is a unit of time, although in fact the years can be measured and the distance.

## How many kilometers per year

In order to understand the meaning of "light year", you first need to remember the school course of physics, especially the section which relates to the speed of light. Thus, the speed of light in vacuum, where it is not affected by various factors, such as the gravitational and magnetic field, suspended particles, the refraction of a transparent medium, etc., is 299 792,5 kilometers per second. You need to understand that in this case, light refers to electromagnetic waves perceived by the human vision.

Less well-known units of distance are light-month, week, day, hour, minute, and second.Quite a long time, the speed of light was considered infinite value, and the first person who calculated the approximate speed of light rays in vacuum, became astronomer Olaf römer in the middle of the XVII century. Of course, his data were very approximate, but the important fact of determining the final value of speed. In 1970 the speed of light was determined with a precision of one meter per second. More accurate results was not achieved until now, as I am having problems with the error of the standard meter.

## Light year and other distance

Because distances in space are huge, measuring them in the usual units, it would be inappropriate and uncomfortable. Based on these considerations, has introduced a special unit of measurement is the light year, distance that light travels for the so-called Julian year (equal to 365,25 days). Given that each day contains 86,400 seconds, we can calculate that in a year a beam of light covers the distance several more than 9.4 trillion kilometers. This value seems huge, but, for example, the nearest star to Earth Proxima Centauri is 4.2 years and the diameter of the milky Way galaxy is over 100 000 light years, that is, those visual observations that can be made now reflect the pattern that existed about a hundred thousand years ago.

The light ray covers the distance from the earth to the moon in about a second, but the sunlight reaches our planet more than eight minutes.

Professional astrophysics the concept of light years is rarely used. Scientists primarily operate units such as the parsec and astronomical unit. A parsec is the distance to the imaginary point at which the radius of Earth's orbit is seen under an angle of one arcsecond (1/3600 of a degree). The average radius of the orbit, i.e. the distance from the earth to the Sun, called an astronomical unit. A parsec is about three light years, or 30.8 trillion kilometers. Astronomical unit is approximately equal to 149,6 million kilometers.