The light year is a measurement of length used in astronomy.
The concept of a light year is often confusing. The presence of the term year makes many people associate the expression with a temporal unit. Light year, however, is a measurement of length that is used in the field of astronomy, and for this reason we do not speak of "taking a light year" but of "being one light year away."
Specifically, a light year is the distance that light travels in a vacuum in the span of one year . Since light travels 299,792,458 meters per second in a vacuum, a light year is an enormous distance: it is equivalent to 9,460,730,472,580.8 kilometers .
As can be seen, the use of the notion of light years allows us to work with simpler figures when the distances are very great, as is the case between planets and other stars. Expressing distances such as 40 or 200 light years, for example, would require many digits if units such as meters or even kilometers were to be used.
Example of light years
Take the case of planet Earth with respect to Proxima Centauri , the star closest to the sun . According to astronomers, Earth is located about 4.22 light years from Proxima Centauri . This means that light takes 4.22 years to travel the distance between our planet and the aforementioned star.
In this way, if a person observes the light emitted by Proxima Centauri today from Earth , they are actually seeing the light that left the star more than 4 years ago. If Proxima Centauri , for some reason, stops existing and emitting light, it would take us more than four years on Earth to notice its disappearance.
The distance between planets and stars is usually expressed in light years.
Minor units
It should be noted that when distances are smaller, similar units such as light minutes or light seconds can be used.
The light minute is, as can be deduced, the distance that an electromagnetic wave travels in a vacuum in the course of one minute, which is equivalent to 17,987,547,480 meters. Among the astronomical distances that are usually expressed using this unit (instead of light year) are that of certain space probes and that between the Sun and the Earth (approximately 8.31 light minutes). In the field of astronomy, the light minute is very useful to indicate the delay that may exist between two given points.
The distance expressed by the light second, for its part, is 299,792,458 meters. This unit of measurement is used to refer to the distance between our planet and certain celestial bodies, such as the Moon (1.2 light seconds), the Sun (500 light seconds), Alpha Centauri (137 million light seconds ), Pluto (20,000 light seconds) and the Andromeda galaxy (80 billion light seconds), among many others.
This alternative to the light year is suitable for measuring distances within the Solar System , as long as they are not smaller than the diameter of Jupiter. In the calculation of intergalactic distances, the light year must be used, or the parsec ( parallax of one arc second ), while for intergalactic distances there is the megaparsec (a multiple of the parsec, which is equivalent to about 3.26 million of light years).
The idea of light years in colloquial language
Outside the field of astronomy , it is common to use this unit of measurement in a figurative sense, to make qualitative comparisons between people or products with the intention of accentuating the great distance that exists between different elements.
Let's look at some example sentences: "I would like my student to go directly to the next grade, since she is light years ahead of her classmates and I fear that she will be bored to the point of frustration," "Between these two televisions there is no point of comparison, since their technologies are light years away .