सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

7
The sidereal day is the time taken by the stars to go
round the earth once. It is called Nākshatra-dina.
Comm. In Hindu mythology gods are supposed to
reside at the north-pole, where one civil day is the same
as one sidereal solar year for the other places; also the
demons are supposed to reside at the south pole so that
their civil day also is equal to a sidereal solar year. But,
what is day to the gods is night to the demons and vice-
versa.
If we call the earth, the moon of the moon so to say,
which it is so, when it is the moment of new moon for the
earth, it is the moment of Full Moon to the Moon. Thus
what is a Chāndra-māsa to the earth may very well be
called with respect to the Moon a Bhauma-māsa. In
Hindu mythology the manes are supposed to take residence
on the surface of the Moon. We know from modern
astronomy that the moon revolves about her axis once
roughly in a lunation. Thus for 'the man on the moon',
a day is roughly equal to our lunation. So if the manes
were to reside on the moon, their day is equal roughly
to a lunation of ours. We say 'roughly' because as we
see under the chapter of the lunar eclipse, the moon
almost shows the same face to the earth on account of
what are called 'librations in longitude'. On this count
the time of rotation of the moon does not exactly coincide
with the time of a lunation.
A civil day for a place is also the civil day for every
place of the earth so that it is called the earth's day. By
'day' here we do not mean the time when the Sun is
above the horizon, for that time differs from place to place
on the earth. A civil day is the sum-total of the duration
of day and the duration of night for any place and it will
be seen that this is the same for the entire earth except at
the places having perpetual day. The word Saura Sāvana
is used to signify that the time that elapses between two
consecutive rises of any other planet is termed the Sāvana