Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s8: (4), (5) Adhikāras on Eclipses of the Sun and the Moon
Bhāratīya Jyotiḥśāstra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s8
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(4), (5) Adhikāras on Eclipses of the Sun and the Moon
v2.c12.s8.1
That the cause of the lunar and solar eclipses is not the demon Rāhu, but the earth's shadow in the case of the lunar eclipse and the moon in the case of the solar eclipse, was known since the times of Varāhamihira and Āryabhaṭa who are the oldest known ‘human’ authors of astronomical works. While declaring that he would describe the cause of the eclipses in such a way as would reconcile the teachings of the Śrutis, Smṛtis and Jyotiṣa Saṃhitā with the astronomical theory, Brahmagupta* observes “Rāhu entering the earth's shadow envelops the moon in the lunar eclipse, and entering the Moon, it envelops the Sun at the time of the solar eclipse”, and Bhāskarācārya** also has explained the phenomena in the same way.
v2.c12.s8.2
PARALLAXES
v2.c12.s8.3
The parallax of the moon has to be taken into consideration in the case of the solar eclipse. Our works regard the maximum value of parallax as equal to 1/15 of the planet's motion; which means that the maximum mean parallax of the moon is 52' 42" and that of the sun is 3'56" ; compared with the findings of modern astronomy there is only a slight error in the value of the moon's parallax; but that of the sun is very much mistaken. Modern discoveries show that the maximum value of the equatorial horizontal parallax is 57' 1" for the moon and 8.6" for the sun.
v2.c12.s8.4
Hipparchus has determined† 57' as the moon's parallax and 3' as that of the sun, while Ptolemy had found it to be 58' 14" for the moon and 2'51" for the sun. It shows that our people have not taken these values from either.
v2.c12.s8.5
Owing to the brilliance of the sun, the eclipse is not visible even if the twelfth part is eclipsed; whereas in the case of the moon, the eclipse is visible even if the sixteenth part of the lunar orb is eclipsed; Bhāskarācārya has remarked that an eclipse should not be declared if its calculated magnitude comes to be less than this. Almost all other writers have similarly observed that the eclipse becomes invisible, more or less within the same limits of observation. But on 19th August 1887, there was a solar eclipse and the magnitude of the eclipse was 7/100 at Gwalior, i.e. equal to about the fourteenth part of the solar orb. It was seen by Visaji Raghunath Lele with naked eyes, as also through a glass smeared with lamp-black and it was seen quite clear. He, however, found that it was very risky to see such a small eclipse with the naked eye, for the eye-sight is likely to be very much impaired.