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

474
the Sun will have to overtake Jupiter and not vice versa.
When it is the Sun that is to overtake, taking a position
of Jupiter near the western horizon gradually the planet
gets fainter and fainter as the Sun approaches him from
west to east. Ultimately one evening the planet ceases
to be perceptible within a particular distance of the Sun.
This we call heliacal setting of the planet. Having thus
set in the west, after a few days the planet rises in the
east. This is so because, after the planet's heliacal setting,
the Sun gradually approaches the planet from west to east;
at a particular moment will have a longitude equal to that
of the planet and then gradually gains in longitude over
the planet. After a few days, in the eastern horizon, the
planet will emerge from the rays of the Sun before Sun-
rise; it is not the planet moving west from east but it is
the Sun moving from west to east so that the Sun recedes
away from the planet towards east. The planet also will
be having a motion from west to east but it being slower
than that of the Sun, the latter gains over the former in
its motion from west to east.
In the case of the inferior planets, say for example,
Mercury, the velocity of Mercury is greater than that of
the Sun; as such, Mercury will be overtaking the Sun and
not vice versa. Thus in the eastern horizon, it is Mercury
that enters the rays of the Sun, going from west to east,
so that he sets in the east. After a few days of this
heliacal setting, Mercury acquires a longitude equal to
that of the Sun, and while overtaking the Sun from west
to east, he emerges out of the rays of the Sun in the west,
which is therefore heliacal rising. But, when Mercury is
retrograde, the case is different. Some days after heliacal
rising in the west, Mercury attains his maximum elonga-
tion and then begins to retrograde. The elongation then
gradually decreases, and he will set again in the rays of
the Sun in the west itself. A few days thereafter, still
continuing retrograde, he emerges out of the Sun's rays