# What is a Light Year

Light year is a measure which is used to calculate the distance travelled by light in an empty space or a vacuum in a year. The movement of light in the empty space is close to 299.792 km per second. When calculated, the sun travels approximately 9.4 trillion km in a year. This measurement is normally used in calculating the distance of stars from our solar system or from our planet.

Along with the concept of light years, come the concepts used by scientists called the light seconds and light minutes. The light minutes and the light seconds are also measure of distance travelled by light. The light years are reduced to light minutes or seconds to make the calculations easier. For example, the distance of our planet earth from the sun is 8.3 light minutes. This means that the light which is emitted from the sun takes 8.3 minutes to reach the earth.

Our solar system is in a galaxy called as the Milky Way. In this galaxy there are billions of stars and the nearest star to the solar system is a star called the Proxima Centauri. This distance is 4.2 light years away from the solar system. Closer to Proxima Centauri is the star that is known as the double Centauri A and the double Centauri B which is located at a distance of 4.3 light years. When it is mentioned Proxima Centauri is located at 4.2 light years, it means that the light takes 4.2 light years to reach the star.

The other astronomical unit like the lights years is the Parsec. Each Parsec is equal to 3.26 light years. The introduction of Parsec as an astronomical unit has made the procedure of calculating the distance between celestial bodies more convenient. Another important concept discussed in Parsec is parallax. Parallax refers to the change of position of a object with respect to the viewers position. Through many experiments it is known that the distance has inverse proportionality with parallax. A kilo parsec is the term given for a thousand parsecs. A mega parsec is the term given for a million parsecs. The mega parsec is also mentioned as Mpc for calculation purposes.

Light month is the month or 30 days for the light travel. When calculated, the light month is one twelfth of the light year. This concept of a light month is mentioned and used in Hayeden planetarium.

Hence, light year is very useful to calculate the distance travelled by light in this universe which is considered to be infinite. Many new celestial bodies are found and its distances are easily calculated with the help of light years.