Question

The nearest star to the earth (apart from the sun) is ‘Alpha Centauri’ which is about ______ away from the earth
(A) $4.3$ light years
(B) $3.26$ light years
(C) $4.3 \times {10^{12}}km$
(D) $3.26 \times {10^{15}}km$

Answer 1

The light-year is a unit of distance taken to be the distance a light wave will travel in one year. It has been known that it will take about 4 years for light to get to the alpha Centauri.

Complete step by step answer
Besides the sun, there are billions of stars in our galaxy alone (known as the Milky Way) galaxy. And of course, there are stars in other galaxies too.
Generally, there are different types of stars, some are very hot and some are not so hot, some are large and some are small. Like the sun, some may have planets orbiting them, while most are alone with no planets around them. Some stars are actually so close to each other that they can be called a system of stars. These stars have their gravitational field around each other such that it is strong enough to make them orbit one another or about a common centre of mass.
The closest of these other stars to us is known as Alpha Centauri. As seen from the earth, due to its closeness the Alpha Centauri is the third brightest star visible from the surface of the earth even without the telescope. It is known that it will take light about 4 years to reach the star. Hence, the distance between the star and the earth is $4.3$ light years (because the distance travelled by light in a year is called 1 light year.

Hence, the correct answer is A.

Note
We should note that Alpha Centauri is actually a star system with three stars. Alpha Centauri A, Alpha Centauri B and Proxima Centauri. The closest to us of these is the Proxima Centauri which is actually about $4.2$ light years away.