The distance travelled by light year. 1 light year = 9.46 × 10
m Q. 2.10. How many light years are there in one metre? (H.P.S.S.C.E. 2006 S) Ans. Now, 1 light year = 3 × 10
m s
× (365 × 24 × 60 × 60) s = 9.46 × 10
m 1 m = \frac{1}{9.46 × 10
= 1.057 × 10
light year Q. 2.11. Define astronomical unit. (H.P.S.S.C.E. 2006 S) distance of the sun from the earth.
The Correct Answer and Explanation is:
Q.2.10. How many light years are there in one metre?
(H.P.S.S.C.E. 2006 S)
Answer:
We know:
1 light year is the distance that light travels in one year.
Speed of light, c = 3 × 10⁸ m/s
Time in one year = 365 × 24 × 60 × 60 = 31,536,000 seconds
So,
1 light year = 3 × 10⁸ m/s × 31,536,000 s
= 9.46 × 10¹⁵ metres
Now,
To find how many light years are in 1 metre:1 metre=19.46×1015 light years1 \text{ metre} = \frac{1}{9.46 \times 10^{15}} \text{ light years}1 metre=9.46×10151 light years
= 1.057 × 10⁻¹⁶ light years
Q.2.11. Define Astronomical Unit (AU).
(H.P.S.S.C.E. 2006 S)
Answer:
An astronomical unit (AU) is the average distance between the Earth and the Sun.
1 AU = 1.496 × 10¹¹ metres
Explanation
In astronomy, very large distances are involved, making it impractical to use regular units like metres or kilometres. Instead, scientists use specialized units such as the light year and the astronomical unit (AU) to express these vast measurements.
A light year is the distance light travels in one year in a vacuum. Since light moves at an astonishing speed of 3 × 10⁸ metres per second, and there are 31,536,000 seconds in a year, the total distance light covers in a year is:Distance=speed×time=3×108×31,536,000=9.46×1015 metres\text{Distance} = \text{speed} × \text{time} = 3 × 10⁸ × 31,536,000 = 9.46 × 10^{15} \text{ metres}Distance=speed×time=3×108×31,536,000=9.46×1015 metres
This is a huge number, which makes the light year a convenient unit for expressing distances between stars and galaxies.
Conversely, if we wish to express 1 metre in terms of light years, we take the reciprocal:1 metre=19.46×1015=1.057×10−16 light years1 \text{ metre} = \frac{1}{9.46 × 10^{15}} = 1.057 × 10^{-16} \text{ light years}1 metre=9.46×10151=1.057×10−16 light years
This value is extremely small, showing how vast a single light year really is.
Another important unit is the Astronomical Unit (AU). It is defined as the average distance from the Earth to the Sun, which is about 1.496 × 10¹¹ metres. This unit is especially useful for measuring distances within our solar system.
By using units like the light year and AU, astronomers can communicate enormous distances more efficiently and clearly in their observations and research.
