The instrument is a building
Ulugh Beg’s observatory in Samarkand is not a small tube. A great sextant is set in a trench, a meridian arc of brick and marble, tall enough that a star’s altitude can be read with a precision the hand-held instruments of the court cannot match. Work begins around 1420. The tables, the Zij-i Sultani, are issued in 1437.
A school stands with him: Qāḍīzāda al-Rūmī, Jamshīd al-Kāshī, ʿAlī Qushjī. This is not a lone watcher. It is a household of calculation.
The catalogue
About a thousand stars, positions measured again, not merely copied from the Almagest. Later Europe will take a long time to match the care. The book is Persian. The lamps are the same lamps Al-Sufi drew twice. The office is measure, not a new sky.
Question
What kind of instrument is a building you can walk into?