as·tral /ˈastrÉ™l/ Adjective Of, connected with, or resembling the stars: "astral navigation". Of or relating to a supposed nonphysical realm of existence in which the physical human body is said to have a counterpart.
This library implements some of Jean Meeus's algorithms in Javascript. The implementation follows the one of PyCalCal which itself takes inspiration from the colossal work of Reingold and Dershowitz.
Jean Meeus "Astronomical Algorithms" Willmann-Bell, Inc.; 2nd edition (1998 with corrections as of June 15, 2005); ISBN: 0-943396-61-1
Nachum Dershowitz, Edward M. Reingold "Calendrical Calculations" Cambridge University Press; 3rd edition (December 10, 2007); Paperback; ISBN-13: 9780521702386