The numbers are usually assigned in the order of increasing right ascension within each constellation. However, because of the effects of precession, they are now slightly out of order in some parts. This method first appeared in John Flamsteed's Historia Coelestis Britannica, a book that was published by Edmond Halley and Isaac Newton together in 1712.
- "Naming Astronomical Objects". International Astronomical Union (IAU). Retrieved 2009-01-30.
- "Naming Stars". Students for the Exploration and Development of Space (SEDS). Archived from the original on 2010-05-31. Retrieved 2009-01-30.