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

264
Comm. Evident.
Verse 45. Definition of Dikjyā H sin (azimuth). The
angle between any vertical and the Prime-Vertical
measured on the horizon is what is called Digamsa and its
H́ sine is known as Dik-jyā either in the Eastern hemi-
sphere or the Western.
Comm. In modern astronomy azimuth is measured
along the horizon from the north point towards the east
point round the horizon. In Hindu Astronomy however,
the azimuth is measured from the East point on either
side and from the West point also on either side specifying
whether it is north or south.
Verse 46 and first half of 47. To obtain the
gnomonic shadow in any arbitrary direction.
Assume Rs / (H sin a) as the equinoctial shadow and
obtain the H sine of the corresponding latitude L. Then
the product of that H sin L and H sin δ divided by
H sin ϕ will give H sin D where D is a hypothetical decli-
nation. With the new L and this D, as the hypothetical
latitude and declination, obtain the meridian zenith
distance by the formula Z + D = ϕ, and through this
m.z d. obtain the shadow, which will be the shadow in the
required direction namely 12 tan (ϕ ± D).
Comm. Let gL be the gnomonic shadow on the
equinoctial day in a given direction given by a°
Digamsa (the Hindu azimuth) and let gN be the shadow in
the same direction on any day. (fig. 45) We know that the
extremity of the gnomonic shadow on the equinoctial day
traces a straight line parallel to the East-West line Eω
at a distance of the equinoctial shadow s because the
Equatorial plane passing through the foot of the gnomon