Humanity in the course of its development used many units to measure the distances between objects. So, in ancient Greece, stages were used, and in ancient Russia, saplings. Currently, the accepted standard for measuring distances on Earth is the meter and its derivatives (millimeter, kilometer and others). In astronomy, they use completely different units of measurement of this magnitude. The article considers the question of what a light year is.
The speed of light and its associated unit of distance
What is a light year? Having heard this question, many people who are not very familiar with astronomy will begin their answer something like this: “This is the year ...”, thus assuming that they are being asked about a unit of time. Such an answer will be incorrect.
What is a light year? The definition can be given as follows: this is the distance that a photon of electromagnetic radiation travels in absolute vacuum, far from the influence of gravitational and magnetic fields for a time equal to one Julian year.
Knowing that the speed of light is 3 * 10 8 m / s, and the Julian year (average value of the Earth year) is 365.25 Earth days, you can get the equivalent distance in meters (kilometers). Answering the question of what a light year is and what it is equal to, let's say that it is equivalent to 9.46 * 10 12 km. There is no special symbol for the light year, therefore the abbreviation "c." Is often used.
To visualize how great is the value of 1 s. g., we note that it is approximately 63 thousand times greater than the distance from the Earth to the Sun.
Below is a video that describes what a light year is.
Light Year and Parsec
Despite the fact that the light year is a huge distance, astronomy often uses a different unit of measurement of the distance between space objects. It is called a parsek. One parsec is approximately 3.26 s. g., and 1 s. g. is 0.31 parsec.
Distances between space objects in light years
Knowing what a light year is, it is interesting to provide information on the distances and sizes of some space objects, expressed in units of measure.
A light year is not used to describe the size of the solar system because it is too small. For example, the 8th planet of our system, Neptune, is only 0.00062 s from the Sun. g., that is, the light from it reaches the periphery of our planetary system in just 5.45 hours.
Most comets that are present in the solar system originate from the so-called Oort Cloud. This cloud is located on the periphery of our system, at a distance of about 1 s. g.
When we go beyond the limits of the solar system, then the light year is useful. So, the closest star to us is Proxima Centauri. It is located at a distance of 4.22 s. g.
The diameter of our galaxy (the Milky Way) is estimated at 150 thousand light years, and this value for the Andromeda Nebula is 240 thousand light years.
Modern telescopes make it possible to observe objects of the Universe located at distances of 13.7 billion light years. That is, if we assume that our planet is in the center of the Universe, then the diameter of the observed sphere will be 27.4 billion light years.