Question

Tarun got to know from his elder brother that the sun is the nearest star and is approximately $150$ million kilometers away from the earth. He wanted to know which is the next nearest star and what is its distance from the earth. His tutor told him that the nearest star is proxima centauri and is at a distance of $4.3$ light years from the earth. Tarun does not know what a light year is. Can you tell him ?

Answer 1

Hint:Some of the farthest galaxies visible to us are billions of light-years away. Astronomers can also calculate how far back in time they are viewing by measuring in light-years. Anything we see in the night sky has already happened because light takes time to reach our eyes.

Complete answer:
A light year is the distance that light travels in a year. A light-year is a unit of distance rather than time (as the name might suggest). A light-year, or six trillion miles, is the distance travelled by a ray of light in a single Earth year.

However, the primary justification for using light years is that the distances we deal with in space are enormous. We easily run into unwieldy numbers only calculating the distance to the nearest star: a dim red dwarf named Proxima Centauri that sits a mere $24,000,000,000,000$ miles away if we stick to miles or kilometres.

Note:As an alternative to the light-year, astronomers use parsecs. A parsec, short for parallax-second, is derived from the use of triangulation to calculate the distance between stars. It is the distance to a star whose apparent location in the sky changes by one arcsecond after Earth orbits halfway around the sun.