The mean distance of the sun from the earth is $1.5 \times 10^8 \text{ km}$ (nearly). The time taken by the light to reach the earth from the sun is.....$\text{min}$

Explain accuracy and precision in measurement.

The moon is observed from two diametrically opposite points $A$ and $B$ on Earth. The angle $\theta$ subtended at the moon by the two directions of observation is $1^{\circ} 54^{\prime}$. Given the diameter of the Earth to be about $1.276 \times 10^{7} \; m$,compute the distance of the moon from the Earth.

What is meant by the angular diameter of the moon?

In an experiment, a set of readings are obtained: $1.24 \ mm, 1.25 \ mm, 1.23 \ mm, 1.21 \ mm$. The expected least count of the instrument used in recording these readings is . . . . . . $mm$.

Explain how time was measured in ancient times. Also,write a note on the cesium clock (atomic clock).