What is "nastulus"

Muḥammad ibn ʿAbd Allāh Nasṭūlus (or Basṭūlus) was a notable 10th-century astronomer and astrolabist. He is known for making the oldest surviving astrolabe, dated 927/928 AD. Another partially preserved astrolabe that bears his signature, "Made by Nasṭūlus in the year 315" of hijra (925 AD), contains the earliest known geographical list on an instrument.

Very little is known about his life. His full name, based on a testimony given by a contemporary astronomer Abu Sa'id al-Sijzi, indicates that he was a Muslim. But some modern historians have suggested that his foreign last name may indicate that he was Greek or Nestorian.