== References ==* Robin M. Green, "Spherical Astronomy", 1985, Cambridge University Press, ISBN 0-521-31779-7* William M. Smart, edited by Robin M. Green, "Textbook on Spherical Astronomy", 1977, Cambridge University Press, ISBN 0-521-29180-1.
* Чичен-Ица* Стоунхендж* Аспект (астрология)* Небесная механика* Эпоха* Robin M. Green, "Spherical Astronomy", 1985, Cambridge University Press, ISBN 0-521-31779-7* William M. Smart, edited by Robin M. Green, "Textbook on Spherical Astronomy", 1977, Cambridge University Press, ISBN 0-521-29180-1.