Units and Measurement

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Year: It is the time taken by earth to complete 1 revolution around the sun in its orbit.

Lunar month: It is the time taken by the moon to complete 1 revolution around the earth in its orbit. 1 L.M. = 27.3 days

Solar day: It is the time taken by earth to complete one rotation about its axis with respect to sun.

Since this time varies from day to day, the average solar day is calculated by taking an average of the duration of all the days in a year and this is called Average Solar day.

1 Solar year = 365.25 average solar day
Or average solar day 1/365 .25 the part of solar year

Sedrial day: It is the time taken by earth to complete one rotation about its axis with respect to a distant star.

1 Solar year = 366.25 Sedrial day = 365.25 average solar day.

Thus 1 Sedrial day is less than 1 solar day.

Shake: It is an obsolete and practical unit of time.

1 Shake = 10^{– 8} sec