Question

Parsec is a unit for measuring
A) The time
B) Very small distances
C) Astronomical distances
D) The arc of a circle

Answer 1

Hint: In every system of measurement of a unit, each quantity is represented by a base unit. For example, in the metric system, the basic unit of length is metre. However, all the lengths measured in the metric system are not directly written in the units of metre. Hence, we make use of powers in terms of the basic unit to measure the quantity.

Complete step by step answer:
The magnitudes in which the units of a quantity are expressed, is based more on convenience of the usage rather than the actual base unit.
For example, if the length of a small tennis ball is to be measured, we measure it in terms of centimetres or 1/100th of a metre. Conversely, if the distance between two cities is to be measured, we measure it in terms of kilometres or 1000 times that of the metre.

Depending on the magnitude of the powers of the basic unit, there are two kinds of units: Microscopic and Macroscopic.
Microscopic units are in powers less than 1/10. Example are centi-, milli-, micro- and nano-
Macroscopic units are in powers above 10 like kilo, mega, giga, tera etc.
However, for extremely large powers such as astronomical distances which have very high powers of kilometres, two special units of length are derived. They are:
i) Parsec
ii) Light Year
Parsec is used to measure distances outside the solar systems. One parsec is equal to 31 trillion kilometres.
1 trillion is equal to ${10^{12}}$. 1 trillion kilometres in metres will be equal to ${10^{12}} \times {10^3} = {10^{15}}$.
Thus, 1 parsec = $31 \times {10^{15}}m$.

Hence, the correct option is Option C.

Note: Another astronomical unit mentioned here is the light year. It is defined as the distance travelled by light in the time interval of 1 year.
1 light year = 9.46 trillion kilometres = $9 \cdot 46 \times {10^{15}}m$
Hence, the unit parsec is greater than light-year.