Moon clouds. The illuminated area of the visible sphere (degree of illumination) is given by formula_3, where formula_4 is the elongation (i.e., the angle between Moon, the observer (on Earth) and the Sun). The gravitational attraction that masses have for one another decreases inversely with the square of the distance of those masses from each other. As a result, the slightly greater attraction that the Moon has for the side of Earth closest to the Moon, as compared to the part of the Earth opposite the Moon, results in tidal forces. Tidal forces affect both the Earth's crust and oceans. The
Union of the Sun and Moon be assured a rebirth in a natural nirmanakaya realm during the bardo of becoming and there reveal buddhahood without further rebirths." Namkha'i and Shane (1986, 1999: p. 91) open the discourse of the 'Song of the Vajra' (Wylie: rdo rje'i glu zhig) an excerpt of the "Union of the Sun and Moon" into the English language and render it thus: <poem> Union of the Sun and Moon The Union of the Sun and Moon () is one of the Seventeen tantras of the esoteric instruction cycle () which are a suite of tantras known variously as: Nyingtik, Upadesha or Menngagde