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

Explain the method to determine the size of a molecule of oleic acid.

Write the ratio of the maximum and minimum time observed in the universe.

What is the accuracy of an atomic clock?

$A$ $LASER$ 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?

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