The difference between the length of a mean solar day and a sidereal day is approximately .......... minutes.

It is a well-known fact that during a total solar eclipse,the disk of the Moon almost completely covers the disk of the Sun. From this fact and the information given below,determine the approximate diameter of the Moon.
Distance of the Moon from the Earth $= 3.84 \times 10^{8} \; m$
Distance of the Sun from the Earth $= 1.496 \times 10^{11} \; m$
Diameter of the Sun $= 1.39 \times 10^{9} \; m$

What is the approximate dimension (thickness) of a molecule of oleic acid?

$(a)$ How many astronomical units $(AU)$ make $1$ parsec?
$(b)$ Consider a sun-like star at a distance of $2$ parsecs. When it is seen through a telescope with $100$ magnification,what should be the angular size of the star? The Sun appears to be $(\frac{1}{2})^{\circ}$ from the Earth. Due to atmospheric fluctuations,the eye cannot resolve objects smaller than $1$ arc minute.
$(c)$ Mars has approximately half of the Earth's diameter. When it is closest to the Earth,it is at about $\frac{1}{2} AU$ from the Earth. Calculate what size it will appear when seen through the same telescope.

What is parallax? Explain the parallax method to measure the distance between the Earth and a planet.

Accuracy of measurement of a physical quantity depends on which factors?