http://www.ast.cam.ac.uk/public/ask/2445 University of Cambridge – Institute of Astronomy – Ask an Astronomer [NB: questionable source as its sources refer back to Wikipedia]
T. Van Flandern & K. Pulkkinen (1980). “Low precision formulae for planetary positions”. Astrophysical Journal, Supplement Series. 31 (3). Bibcode:1979ApJS...41..391V.Quản lý CS1: sử dụng tham số tác giả (liên kết)
Van Flandern, T.; K. Pulkkinen (1980). “Low precision formulae for planetary positions”. Astrophysical Journal Supplement Series. 31 (3). Bibcode:1979ApJS...41..391V. doi:10.1086/190623.
