The Astronomical Observatories of Jai Singh c6.s1.t1.7

c6.s1.t1.7

¹ *Let ABCD* (Plate V) represent the tropic of Capricorn and *CA* the meridian, and let the arc *AF* measure the obliquity of the ecliptic, then the point *S* on the intersection of *BF* and *AC* is on the equator and *SENW* represents the equator, *E* being the eastern point. Similarly by drawing *Os* parallel to *OF* we get *s*, the southern point of the tropic of Cancer and *Cs* the diameter of the ecliptic. The angles *SL* and *WL* measure the latitude (φ) of the place, and by joining *LE* and *L*₁*E* we get *Z*, the zenith, and *H*, the meridian point on the horizon. The opposite point on the horizon is *H*₁ where *El*₁ (=φ) meets the meridian line *NS* produced. To obtain a circle (almucantarat) for altitude *a*, mark off angles (φ±*a* 90°) from *S*, the south point of the equator, (positive direction *S W*) and join both these points to *E*, the east point on the equator: the distance between the points intersepted on the meridian line *NS* is the diameter of the circle of altitude *a*.