Yǔ Jìcái 庾季才
Native of Xīnyě 新野 (Hénán). Active under the Northern Zhōu and early Sui; flourished c. 540–600. Birth and death years not securely recorded.
The principal Northern-Zhōu / early-Sui imperial astronomer-and-astrologer. Held the office of Tàishǐ Zhōng dàfū 太史中大夫 (Senior Grand Master of the Bureau of Astronomy) under the Northern Zhōu. The Suíshū Jīngjí zhì records his works in 115 juàn; the Zhōushū (Northern-Zhōu History) lists 110 juàn. The principal surviving work is the Língtái mìyuàn 靈臺祕苑 (KR3g0017), originally in 110-or-115 juàn but reduced to 15 juàn by Northern-Sòng imperial-decree-revision under Wáng Ānlǐ 王安禮 (Wáng Ānshí’s brother) and the Bureau of Astronomy staff.
The work is a major imperial-court astronomical-and-divinatory compendium: stellar identifications and computations (bùtiān gē and diagrams), region-allotment (fēnyě tǔguī — astrological-geographical correspondences), wind-thunder-cloud-pneumatic divination, and topical divination by sun, moon, planets, and the three-walls / 28-mansions. Through the Northern-Sòng revision, the work became one of the principal late-imperial divinatory-astronomical references.