What is light year?

Light year
The nearest star to our
solar system is Proxima
Centauri.
It is at a distance of
2,68,770 AU. We can note here
that using AU for measuring
distances of stars would be unwieldy.
Therefore,
astronomers use a special unit, called ‘light
year’, for measuring the distance in deep space.
We have learnt that the speed of light in vacuum
is 3 × 108
m/s.
This means that light travels a
distance of 3 × 108
m in one second. In a year
(non-leap), there are 365 days. Each 24 hours, each hour has 60 minutes and each
minute has 60 seconds.
Thus, the total number of seconds in one year
= 365 × 24 × 60 × 60
= 3.153 × 107
second
If light travels at a distance of 3 × 108
m in
one second, then the distance travelled by light
in one year = 3 × 108
× 3.153 × 107
= 9.46 × 1015
m. This distance is known as one light year.
One light year is defined as the distance
travelled by light in vacuum during the period of
one year.
1 Light year = 9.46 × 1015 m.
In terms of light year, Proxima Centauri
is at 4.22 light-years from Earth and the Solar
System. The Earth is located about 25,000 light�years away from the galactic centre.

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