Question

Which of the following is not a unit of time?
A. Parsec
B. Year
C. Second
D. Hour

Answer 1

We will find out the values and definitions of each of the options given. Time is a sense of progression from the past to the future through the present. The standard unit of time is given by the amount of time taken for around 9 billion oscillations between the two hyperfine levels of the ground state of the Caesium 133 atom.

Complete step by step solution:
A unit of time is used to measure a time interval or expressing the duration. The standard unit of time or the SI unit of time is second (s). One second is defined as the duration of 9192631770 oscillations between the two hyperfine levels of the ground state of the Caesium 133 atom.
However, in the earlier times when the concept of the atom wasn’t discovered yet, time was defined by the movements of astronomical objects which appeared after a set interval of time regularly.
Hence, the Sun based time interval, which we currently know as a year, was used in early ages as a measure of time. The year is the time taken by the earth to make a revolution around the sun.
Similarly, the moon-based time interval, which is known as a month, was based on the moon’s orbital period around the earth. Quite a few Hindu calendars still consider the month based on the moon based time interval.
The earth-based time interval was based on the amount of time taken by earth to rotate around its own axis. The time interval could be viewed using a sundial. On the basis of this earth-based time interval of the day, the time interval for week consisting of 7 days and a fortnight consisting of 14 days was derived.
Further, the subdivision of the day, lead to the concept of an hour where 24 hours make a day and the concept of minutes. Hence, 60 seconds make a minute and 60 minutes make an hour.
However, parsec (pc) is a unit of length, which is used to measure large distances of astronomical magnitude. One parsec is about 3.3 light-years or 210000 astronomical units. The value of parsec will be equal to 31 trillion kilometers, upon converting the 3.3 light-years into kilometers.
One light-year is the amount of distance traveled by light in a time interval of 1 year.
One astronomical unit is the amount of distance between the earth and the sun. This distance is approximately equal to 150 million km.

Hence, the Option A, isn’t a unit of time.

Note: Different units based on the Sun based time system are as follows:
The Olympiad, which refers to the time interval of four years.
The lustrum, which refers to the time interval of five years.
The indiction, which refers to the time interval of fifteen years.
The decade, which refers to the time interval of ten years.
The century, which refers to the time interval of one hundred years.
The millennium, which refers to the time interval of a thousand years.