Question

What does it mean when something is $4$ or $5$ light years away from us ?

Answer 1

Hint: In order to solve the given question we will know what is light year and implement our concept and solve the question.Light year is a unit of astronomical distance which is given as the distance travelled by light in one year in vacuum which is $9.4607 \times 10^{12}\,km$ (nearly 6 million million miles). We know that the speed of light in vacuum is 300,000 Km/s. that means light travels 300,000 kilometers in one second.So in one year Light travels 10trillion meters.

Complete answer:
One light-year is equal to 9,500,000,000,000 kilometers. Well, on Earth, a kilometer may be just fine but in universe the kilometer is just too small to be useful. For example, the distance to the Andromeda Galaxy is 21 quintillion km. That is 21,000,000,000,000,000,000 km.

This is a number so large that it becomes tedious to write and hard to interpret. So astronomers use other units of distance. So if one light year equals 9,500,000,000,000 kilometers then 4 light years will be 38,000,000,000,000 kilometers and 5 light years will be 47,500,000,000,000 kilometers.

Note:Many times in our solar system, we tend to describe distances in terms of the Astronomical Unit (AU). The AU is defined as the average distance between the Earth and Sun. That is about 150 million km (93 million miles). Mercury can be said to be approximately 1/3 of an AU from the Sun and Pluto averages about 40 AU from the Sun. The AU, however, is not big enough of a unit when we start talking about distances to objects outside the solar system.