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	Frequently Asked Questions Send to a friend  Printable version  En Español Keywords Gravity  Tides  Sun  Earth's Moon  Earth  Resources FAQs about Earth, Moon, and the Sun Astronomy Gift Shop 2009 Sky Almanac McDonald Observatory logo cap What causes tides?  Ocean tides are caused by the gravitational tug Earth feels from the Moon and Sun. For the most part, the rise and fall of the tides is caused by the gravitational influence of the Moon. The Moon's gravity pulls the ocean surface upward, creating a bulge in the water -- high tide. Locations on Earth perpendicular to the Earth-Moon line experience low tide. That's not the end of the story, however. The Sun also tugs on Earth's oceans, though to a lesser extent. When both Sun and Moon are lined up with Earth, as occurs during the full and new moons, their combined effects yield higher tides than normal, called spring tides. Conversely, when the Sun is at right angles to Earth and Moon, as at the first- and last-quarter phase, the Sun's gravitational influence works against the Moon, and we experience an unusually low, or neap tide. Other FAQs Select FAQ category Earth, Moon, and the Sun The Solar System Space Probes and Human Exploration Stars and Nebulae Astronomers and Observatories Galaxies and Cosmology Stargazing and Star Lore » FAQs about StarDate Online Earth, Moon, and the Sun Links NASA Eclipse Home Page Exploring the Moon Earth Observatory Earth Science Picture of the Day Solar Dynamics Observatory Near-Earth Asteroid Tracking Home Page SpaceWatch Lincoln Near Earth Asteroid Research (LINEAR) Lowell Observatory Near-Earth-Object Search (LONEOS) Common Holidays in Relation to Equinoxes, Solstices & Cross-Quarter Days Earth and Moon Viewer Fireball Data Center Meteorite Central NASA Solar Data Analysis Center (SOHO) North American Meteor Network The Aurora Page Virtual Reality Moon Phase Pictures
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