Al-Sufi made several observations on the obliquity of the ecliptic and the motion of the sun (or the length of the solar year). He also made observations and descriptions of the stars, setting out his results constellation by constellation, discussing the stars positions, their magnitudes and their colour, and for each constellation providing two drawings from the outside of a celestial globe, and from the inside. Al-Sufi also wrote on the astrolabe and its thousand or so uses.
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by: FSTC Limited, Mon 16 July, 2007