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

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Fig. 51
the moments when the Sun is at L and when he reaches
the meridian. is called Nata. In modern astronomy this
Nata is known as the hour angle h and unnata = H - h
where H is the rising hour angle. The time measured by
the arc ME is called Chara. Thus unnata-chara = EN
and H sin EN H sin (90 - h) = H cos h is called Sutra
which is BN shown in fig. 52 representing the Equator.
The corresponding line bn in fig. 53 which represents the
diurnal circle, is known as Kalā. Thus Sūtra = H cos h (26)
and Kalā = (H cos h × H cos δ) / R (27).
When the Sun is in the Southern hemisphere, unnata
is measured by the arc SL or MN ie. (H - h) where H is