Question

the periodic rise and fall of the level of water in the ocean caused by the moons gravity

tide
solstice
ellipse

Explanation:

• Tide: Tides are the periodic rise and fall of sea levels caused by the gravitational forces exerted by the Moon (and to a lesser extent, the Sun) on the Earth's oceans.
• Solstice: A solstice is an astronomical event that occurs twice a year when the Sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days. It has nothing to do with ocean - water level changes due to lunar gravity.
• Ellipse: An ellipse is a geometric shape, a type of conic section. It is not related to the described ocean - water level phenomenon.

Answer:

tide