Which of the following pairs is incorrect?

During a total solar eclipse,the moon almost entirely covers the sphere of the sun. Write the relation between the distances and sizes of the sun and moon.

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

$A$ far-off planet is estimated to be at a distance $D$ from the Earth. If its diametrically opposite extremes subtend an angle $\theta$ at an observatory situated on the Earth,the approximate diameter of the planet is .............

If the angular diameter of the Sun is about $30'$ and its distance from the Earth is $1.5 \times 10^{11} \, m$,then the solar diameter is:

Explain accuracy and precision in measurement.