पञ्चसिद्धान्तिका (आचार्य वराहमिहिर - सूर्य, रोमक, पौलिश, वासिष्ठ एवं पितामह सिद्धान्त)

126 PAÑCASIDDHĀNTIKĀ IV. 54
[छायातः दिक्साधनम्]
छायाऽर्कवर्गयोगा (त्पदेन) भाज्यार्कसंगुणा त्रिज्या |
विषुवज्जीवागुणिता (लम्बक) भक्ता तु सूर्याग्रा || ५२ ||
का (ष्ठ) घ्रयार्क्रमौर्व्या लम्बकहृतया वि (हीन) संयुक्ता |
सूर्याग्रा (ऽज) तुलादौ कर्णघ्नी त्रिज्ययाऽपहृता || ५३ ||
लब्धाङ्गुलानि (को) टिस्ट (च्छा) यावर्गविवरमूलं [यत्] |
स च (बाहुर्दिग्ग्र) हणे सममि (तिः) को (ट्या) तु देयमृजु || ५४ ||
Directions from shadow
52. Twelve times the radius (i.e. 1440) is to be divided by the 'Shadow-
hypotenuse', i.e. the root of the sum of the squares of the shadow and 12. This
multiplied by sine latitude and divided by sin co-latitude and divided by sin
co-latitude is called Sūryāgrā (otherwise well-known as Śaṅkvagram or Śaṅ-
kutalam).
53. From this Sūryāgrā, the sine of the Sun's declination divided by the sine
of co-latitude (which is otherwise called Agrā) should be deducted or added,
according as the Sun is in the six signs beginning with Aries, or the six signs
beginning with Libra, (i.e. according as the declination is north or south). The
result is to be multiplied by the 'Shadow-hypotenuse' and divided by the
radius, (i.e. by 120).
54. What is obtained are termed Koṭi, (or 'Perpendicular'), measured in
digits. The root of the square of the Koṭi deducted from the square of the
shadow is called Bāhu (or 'Base'.) and the Koṭi is to be so constructed as to be
perpendicular to the 'Base', (whose extension both ways is the prime vertical).
Thus the directions are got.
The following are the steps in the work:
(i) Shadow hypotenuse = √(shadow² + 144)
(ii) Sūryāgrā 12 × 120 × sin latitude ÷ (shadow hypotenuse × sin colat.)
(iii) Agrā or Amplitude = sin max. dec. of Sun × sin Sun's long. ÷ sin colat. = sin dec. of Sun ×
120 ÷ sin colat. (The declination is north if the Sun is in the six signs from Aries, and south otherwise)
52a-b. A.C.D. योगा (C.D. योगात्) पदे विभाज्यार्क      c. A. °ग्रा च तुलादौ
  b. D. संगु(णिता] त्रिज्या |