moontide

Moontide refers to the regular rise and fall of the Earth's oceans produced primarily by the gravitational pull of the Moon, with the Sun contributing a significant secondary effect. The term appears in oceanography, coastal science, and nautical contexts to describe tides that are driven by the Moon’s gravity in concert with the Sun.

The mechanism involves the Moon’s gravity creating bulges in the ocean on the side of Earth that is closest to the Moon and on the opposite side. The Sun also exerts a gravitational force, and the two bodies interact. When the Sun, Moon, and Earth are aligned during new moon and full moon phases, their gravities reinforce each other, producing higher high tides and lower low tides, known as spring tides. When the Moon is at first and third quarter, the Sun and Moon are at right angles relative to Earth, causing lower high tides and higher low tides, known as neap tides. The actual tidal range varies with coastline geometry, seafloor topography, water depth, and weather conditions.

Along a coast, tides often follow a semi-diurnal pattern (two high tides per day) or a mixed pattern, with the exact timing shifting roughly 50 minutes later each day due to the Moon’s orbit. The resulting rise and fall of water levels influence coastal ecosystems, navigation, anchorage conditions, and tidal energy potential. While the term moontide emphasizes the Moon’s role, the tides are a combined effect of celestial mechanics and local geography.