Tides are caused primarily by the gravity of which celestial body?

• A. The Sun
• B. The Moon
• C. The Earth
• D. The Wind

Answer: (B)

Tides arise from the gravitational pull of bodies outside Earth acting on its oceans. The Moon is much closer to us, so its gravity creates the strongest tidal effects: the near side of Earth is pulled a bit more than the far side, producing the bulges that become high tides as the planet rotates beneath them. The Sun also exerts gravity, but it’s much farther away, so its tidal influence is weaker—about half as strong as the Moon’s. That’s why the Moon is the primary driver of tides. When the Sun and Moon line up, their effects add and tides become higher (spring tides); when they’re at right angles, tides are reduced (neap tides).