How is time regulated in a wristwatch and a cesium clock?

Why is the parallax method not used to measure the distance of stars that are $100$ light-years away?

$A$ cuboidal block has dimensions $(1.5 \times 1.5 \times 1.0) \ cm$. What is the total surface area of the cuboid (in $cm^2$)?

The angle of $1^{\prime}$ (minute of arc) in radian is nearly equal to

$A$ $LASER$ is a source of very intense,monochromatic,and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. $A$ laser light beamed at the Moon takes $2.56 \; s$ to return after reflection at the Moon's surface. How much is the radius of the lunar orbit around the Earth?

What is the accuracy of an atomic clock?