what causes the tides

Tides are mainly caused by the Moon’s gravity pulling on Earth’s oceans, with a smaller but important contribution from the Sun’s gravity and the rotation of the Earth.

Basic idea

As the Moon pulls on Earth, the oceans form two bulges: one on the side facing the Moon and one on the opposite side. These bulges move as Earth rotates, so a coastline usually experiences two high tides and two low tides roughly every 24 hours.

Why the Moon matters most

• The Moon is much closer to Earth than the Sun, so its tidal pull is about twice as strong as the Sun’s, even though the Sun is more massive.

• Tides are driven by the difference in gravitational pull across Earth (near side vs center vs far side), and that difference is greater for the Moon.

Two high tides, two low tides

• Water on the side closest to the Moon is pulled slightly more strongly, creating one high-tide bulge toward the Moon.

• Water on the far side is pulled less strongly than Earth’s center, so Earth is pulled slightly away from that water, creating a second bulge.

• Areas under the bulges have high tide; areas between them have low tide.

Role of the Sun: spring and neap tides

• When the Sun, Moon, and Earth line up (new moon and full moon), their pulls combine to make spring tides (extra-high highs and extra-low lows).

• When the Sun and Moon are at right angles (first and third quarter), they partially cancel, giving neap tides with a smaller tidal range.

Why tides differ from place to place

Real tides are not simple, because:

• Continents block the movement of water, changing the pattern of bulges.

• Ocean depth and shape of coastlines alter how the tidal wave propagates and can amplify or weaken the range.

• In some regions, tides rotate around points with almost no vertical change (amphidromic points).

Quick recap

• Main cause: Moon’s gravity, plus the Sun’s gravity.

• Two bulges: one facing the Moon, one on the opposite side.

• Earth’s rotation + these bulges = daily high and low tides.

• Alignment with the Sun gives stronger spring tides; right-angle alignment gives weaker neap tides.

Would you like a simple analogy with diagrams (described in words) to help you visualize the two tidal bulges?