Treatise on the Sun

7. At the precise moment of the full moon pūrṇimānta; the end of the 15th lunar day, the Sun and the Moon are equal in degrees and minutes, separated by six signs original: "bhārddha-bhāga"; exactly 180 degrees. 8. Having calculated the elapsed time in nadis units of 24 minutes from the moment of alignment, and applying the necessary corrections, the two bodies are brought to the same minute of longitude. The position of the node pāta; the ascending or descending node of the Moon at that time must also be calculated.

9. In an eclipse of the Sun, the Moon acts as the obscurer chādaka; being positioned below the Sun, it blocks the light like a cloud. 10. In a lunar eclipse, the Earth's shadow becomes the obscurer. Moving eastward, the Moon enters the shadow of the Earth; thus, a lunar eclipse occurs. 10.

To determine the magnitude of the eclipse, take the latitude of the Moon vikiṣepa; the angular distance of the Moon from the ecliptic at that moment. Calculate half the sum of the diameters māna; measure of the eclipsed body and the obscuring body. Subtract the latitude from this half-sum; the remainder is called the obscured portion channa. 11.

If this remainder is greater than the diameter of the eclipsed body, the eclipse is total sakala; otherwise, it is partial. If the Moon's latitude is greater than the half-sum of the diameters, no eclipse is possible original: "grāsa-sambhava"; the possibility of a "bite" or seizure. 12.

Take half the sum and half the difference of the diameters of the eclipsed and obscuring bodies separately. Square each and subtract the square of the Moon's latitude; the square roots of these two results are the bases pada. 13.

Multiply these by sixty and divide by the difference between the daily motions bhukti of the Sun and Moon. The results provide the half-duration stityardha of the eclipse and the half-duration of totality vimardārdha in nadis and smaller units. 14.

The motions of the planets, multiplied by the half-duration and divided by sixty, should be subtracted from or added to the planetary positions. This process must be repeated until the positions are exact. 15. Through these two values, the half-duration and half-totality are repeatedly refined; otherwise, the results for the minutes of the node pāta would be inaccurate. 15.

16. At the end of the true lunar day sphuṭa-tithi, one should declare the middle of the eclipse madhya-grahaṇa. By subtracting and adding the half-duration, the times of first contact grāsa and last contact mokṣa; release are determined. 17. Similarly, by subtracting and adding the half-duration of totality, the moments of immersion nimīlana; the start of totality and emergence unmīlana; the end of totality are found in the case of a total eclipse. 17.

18. Now, for the eclipse at any desired time: Subtract the desired time from the half-duration. Multiply this by the difference in the daily motions of the Sun and Moon, and divide by sixty. This gives the perpendicular minutes koṭi-liptā. 18. 19. In a solar eclipse, these perpendicular minutes must be corrected for parallax. These are known as the true perpendicular minutes sphuṭa-koṭi-kalā. 19.

20. The Moon’s latitude is the base bhuja. The square root of the sum of the squares of the base and the perpendicular is the hypotenuse shrava; the distance between the centers of the two bodies. Subtracting this from the half-sum of the diameters gives the instantaneous obscured portion tatkālika-grāsa. 20. One should subtract the desired time from the middle of the eclipse...