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

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day pertaining to that planet. Thus the Chāndra-Sāvana
day is roughly equal to 24 hrs–52' and this is the longest
of the Sāvana days pertaining to the planets. The shortest
Sāvana days is that of the Saturn, since Saturn moves a
very little along the ecliptic and his Sāvana day is there-
fore just a little longer than the sidereal day. This nomen-
clature brings in the phenomenon that the Sāvana day of a
retrograde planet happens to be less than a sidereal day.
But in a given time, which is sufficiently long like a yuga,
the Sāvana days of a planet are equal to the number of
sidereal revolutions in that period minus the number of
the planetary revolutions in the same period. This will
be constant for a given planet in such a long period,
though individual days happen to be some shorter and
some longer than a sidereal day.
The modern sidereal day is the time between two
consecutive rises of the equinoctial points and as the equi-
noctial points have a slow retrograde motion, the modern
sidereal day is just a little shorter than the Hindu sidereal
day, which does not take cognizance of the revolution of
the equinoctial points round the earth in reckoning diurnal
motion. The Hindu astronomers speak of the revolution of
the stars only around the earth in the context of diurnal
motion. It will be noted that the Saura-Savana day or the
civil day will not be of the same duration, since the Sun has
unequal motion amongst the stars from day to day. When
the Sun is in perigee and has the max. daily velocity, his
Sāvana day at that moment is the longest and the Saura-
Sāvana day when the Sun is in apogee will be the shortest.
Though in Indian Chronology a day is divided into
sixty ghatis for convenience, these ghatis are evidently
longer than the Nākshatra-ghatis or the sidereal ghatis,
which are of a fixed duration. Thus a Sāvana ghati is a
little longer than a Nākshatra-ghati and what is more, a
Saura-Sāvana ghati is of a variable duration from day to
day, the variation being of course very small.