Thompson, Robert Bruce; Thompson, Barbara Fritchman (2005-06-24). Astronomy Hacks. "O'Reilly Media, Inc.". p. 34. ISBN9780596100605. Archived from the original on 2022-04-19. Retrieved 2009-11-03.
Thompson, Robert Bruce; Thompson, Barbara Fritchman (2005-06-24). Astronomy Hacks. "O'Reilly Media, Inc.". p. 34. ISBN9780596100605. Archived from the original on 2022-04-19. Retrieved 2009-11-03.