ब्राह्मस्फुटसिद्धान्त (ब्रह्मगुप्त - शून्य, कुट्टक, बीजगणित एवं सम्पूर्ण २१ अध्याय सान्वय सटीक)

ARABS ON MOTIONS OF FIXED STARS 45
Here we finish our review of ancient astronomy. We have
omitted as not coming within our province several valuable
contributions to science which did not deal with cosmology or
planetary theory. But even with this limitation enough has
been said to show that when Europeans again began to occupy
themselves with science they found astronomy practically in the
same state in which Ptolemy had left it in the second century.
But the Arabs had put a powerful tool into their hands by alter-
ing the calculus of chords of Ptolemy into the calculus of sines or
trigonometry, and hereby they influenced the advancement of
astronomy in a most important manner.
References

1. Peter Doig : A Concise History of Astronomy London
3. J.L.E. Dreyer : A History of Astronomy from Thales to
   Kepler Dover publications, 1953 (chapter
   XI reproduced).
4. Satya Prakash : Founders of Sciences in Ancient India,
   Delhi, 1965.