Question -
Answer -
The Sun is nearly 150,000,000 kilometres (150 million km) away from the Earth.
The next nearest star to the Earth after the Sun is Alpha Centauri. It is at a distance of about 40,000,000,000,000 km from the Earth. Some stars are even more farther away. It is not convenient to express such distances in kilometres.
Such large distances are expressed in another unit known as light year. One light year is the distance travelled by light in one year.
If we say that a star is eight light years away from Earth, it means that the light from that star will reach the Earth in eight years.