What is the daily rise and fall of sea level caused by the Moon's gravity called?

• A. Eclipses
• B. Waves
• C. Tides
• D. Currents

Answer: (C)

Tides are the daily rise and fall of sea level caused by the Moon's gravity. The Moon's gravity pulls more strongly on the side of Earth that's closest to it, drawing the nearby ocean water upward and creating a bulge. On the opposite side, the pull is weaker and inertia causes another bulge as the Earth is pulled away from that water. As the planet rotates, each location moves through these bulges, producing high tides when a bulge passes overhead (or far from it) and low tides in between. Typically you’ll see two high tides and two low tides each day, roughly every 12 hours and 25 minutes. The Sun also affects tides, sometimes amplifying them (stronger during alignment) or reducing them (when at right angles). All of this specific, regular rise-and-fall process is what we call tides.