The unit of time measurement is the same among all nations. Practically it is 1/86400 of the mean solar day, but really it is a perfectly arbitrary unit, as the length of the mean solar day is not constant for any two periods of time. There is no constant natural unit of time.

1 minute

=

60 seconds.

1 hour

=

60 minutes, 3600 seconds.

1 day

=

24 hours, 1440 minutes, 86,400 seconds.

1 sidereal day

=

86164.1 seconds.

1 sidereal month

=

27.321661 mean solar days (average).

1 lunar month

=

29.530589 mean solar days (average).

1 anomalistic month

=

27.544600 mean solar

days (average).

1 tropical month

=

27.321582 mean solar days (average).

1 nodical month

=

27.212222 mean solar days (average).

Mean solar year

365 d. 5 h. 48 m. 46.045 s. with annual variation of 0.00539.

The change in the length of the mean sidereal day, i.e.. of the time of the earth's rotation upon its axis, amounts to 0.01252 s. in 2400 mean solar years.

- Physical Tables.