Geophysics to every area of the Earth sciences. To provide a clearer idea of what constitutes geophysics, this section describes phenomena that are studied in physics and how they relate to the Earth and its surroundings. The gravitational pull of the Moon and Sun give rise to two high tides and two low tides every lunar day, or every 24 hours and 50 minutes. Therefore, there is a gap of 12 hours and 25 minutes between every high tide and between every low tide. Gravitational forces make rocks press down on deeper rocks, increasing their density as the depth increases. Measurements
Sun and Moon (Middle-earth) Sun and Moon (Middle-earth) The fantasy author J. R. R. Tolkien of Middle-earth fame included Earth's sun and moon for the cosmology of his myths of Arda. These astronomical bodies appear in various versions of "The Silmarillion", a history of a world, called Middle-earth populated by Elves and other fantastic creatures as well as Men. A version of "The Silmarillion", edited by the author's son and literary executor Christopher Tolkien, was posthumously published in 1977. However the Sun and Moon already appear in the author's writings dating from the 1920s. The sun and moon in Tolkien's legendarium were described in