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

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presumed that all the other planets including the Sun would
be traversing the same linear distance during the course of
a day. This led to a wrong estimate of the Sun’s distance
as well as his spherical radius. Also, they supposed wrongly
that the parallax of the Sun also would be equal to 1/15th
of his daily arcual motion.
Their estimate of the spherical diameter of the Moon
was, however, very near the truth, for, they argued, that
if 790′-35″ angular motion per day corresponded to 11858¾
Yojanas in linear measure, to what linear measure did the
angular diameter of the Moon namely 32′-0″-9′′′ corres-
pond? The answer was
11858¾ × 32′ 1/400
------------------ = 480 Yojanas.
790′-35″
[चित्र: Fig. 94]
Fig. 94
It may be here pointed out that there is a relation
between the angular radii of two celestial bodies as seen
from each other and their mutual horizontal parallaxes
(Fig. 94). Let E and M bet he centres of the Earth and
the Moon respectively. E M̂ A = horizontal parallax of
the Moon = angular radius of the Earth as seen from the
Moon and B Ê M = Angular radius of the Moon = Hori-
zontal parallax of the Earth as seen from the Moon. Thus,
we see that the Earth will be seen from the Moon, as a
Moon with an angular radius equal to 57′. In other words
our Earth will be a Moon to our Moon, having nearly 16
times the area of our Moon’s disc.