e has depicted. And so with the firmament and the other
constellations, they move round the earth and sea in glittering array,
completing their orbits according to the spherical shape of the heaven.
4. They are all visible or invisible according to fixed times. While six
of the signs are passing along with the heaven above the earth, the
other six are moving under the earth and hidden by its shadow. But there
are always six of them making their way above the earth; for,
corresponding to that part of the last sign which in the course of its
revolution has to sink, pass under the earth, and become concealed, an
equivalent part of the sign opposite to it is obliged by the law of
their common revolution to pass up and, having completed its circuit, to
emerge out of the darkness into the light of the open space on the other
side. This is because the rising and setting of both are subject to one
and the same power and law.
5. While these signs, twelve in number and occupying each one twelfth
part of the firmament, steadily revolve from east to west, the moon,
Mercury, Venus, the sun, as well as Mars, Jupiter, and Saturn, differing
from one another in the magnitude of their orbits as though their
courses were at different points in a flight of steps, pass through
those signs in just the opposite direction, from west to east in the
firmament. The moon makes her circuit of the heaven in twenty-eight days
plus about an hour, and with her return to the sign from which she set
forth, completes a lunar month.
6. The sun takes a full month to move across the space of one sign, that
is, one twelfth of the firmament. Consequently, in twelve months he
traverses the spaces of the twelve signs, and, on returning to the sign
from which he began, completes the period of a full year. Hence, the
circuit made by the moon thirteen times in twelve months, is measured
by the sun only once in the same number of months. But Mercury and
Venus, their paths wreathing around the sun's rays as their centre,
retrograde and delay their movements, and so, from the nature of that
circuit, sometimes wait at stopping-places within the spaces of the
signs.
7. This fact may best be recognized from Venus. When she is following
the sun, she makes her appearance in the sky after his setting, and is
then called the Evening Star, shining most brilliantly. At other times
she precedes him, rising before day-break, and is named the Morning
Star. Thus Mercury an
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