Question 3: Explain several phenomena occurring naturally which could serve reasonable time standard.
Many repetitive phenomena occurring in nature can be reasonable time standards. Their periodic occurrences can be divided into suitable intervals to measure the time. Following are some of the naturally occurring phenomena that could be used as time standard.
Rotation of earth around the sun
Earth revolves around the sun in a periodic way. The duration (= 1 year, though very long) can be used to measure the time. However, due to the lengthy time period, it is impractical to be used in our daily life.
Spinning of earth around its own axis
Like its orbital motion, earth also spins about its own axis. This repeatedly occurring phenomenon is used for the measurement of time in our watches. One such spin is divided into 24 hours and subsequent smaller units (minutes and seconds). This measurement is quite suitable for the use in our daily life.
Stars seem to change their position due to the spinning of earth about its axis and can be used as time standard. However, the limitation is the stars are not visible during day times or when the sky is cloudy.
It is still common to see stars and guess about the time during night time. The reason is the earth is spinning about its own axis and the stars are considered to be fixed in space. With the spin of earth we also change our position. So we feel as the stars are changing their position all the night (and day, in fact!)