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Practical units used for measuring time:
(i) Solar day:
It is the time taken by the earth to complete one rotation about its own axis w.r.t. the sun.
(ii) Sedrial day:
It is the time taken by the earth to complete one rotation about its own axis w.r.t. a distant star.
(iii) Solar year:
It is the time taken by the earth to complete one revolution around the sun in its orbit.
1 solar year = 365.25 average solar days = 366.25 sedrial days
(iv) Tropical year:
The year in which there is total solar eclipse is called tropical year.
(v) Leap year:
The year which is divisible by 4 and in which the month of February has 29 days is called a leap year.
(vi) Lunar month:
It is the time taken by the moon to complete one revolution around the earth in its orbit.
1 lunar month = 27.3 days
(vii) Shake:
It is the smallest practical unit of time.
1 shake = 10-8 s