↑p. 394, The Universal Book of Astronomy, from the Andromeda Galaxy to the Zone of Avoidance, David J. Dsrling, Hoboken, New Jersey: Wiley, 2004. ISBN 0471265691.
↑p. 314, Collins Dictionary of Astronomy, Valerie Illingworth, London: Collins, 2000. ISBN 0-00-710297-6.