- Why are there two tidal bulges? I thought gravity only pulled water toward the Moon.
- The bulge on the Moon-facing side is indeed due to the Moon's gravity pulling water toward it. The bulge on the far side is caused because the Moon's gravity pulls the solid Earth more strongly than it pulls the water on the far side. This effectively leaves the water behind, creating a second bulge. It's the difference in gravitational force, not just the direction of pull, that creates both bulges.
- If the bulges are aligned with the Moon, why are high tides about 12.4 hours apart and not exactly 12?
- The Earth rotates 360 degrees in about 24 hours. However, in that time, the Moon has also moved a small distance along its orbit. Therefore, a point on Earth must rotate a little more than 360 degrees to catch up to the same position relative to the Moon. This extra rotation takes about 50 minutes, making the tidal cycle—from one high tide to the next—approximately 12 hours and 25 minutes, or 12.4 hours.
- Does this simulator show real tide heights and times?
- No, this simulator uses the simplified 'equilibrium theory' of tides, which assumes a perfectly water-covered Earth that responds instantly to gravitational forces. Real tides are much more complex due to continents, varying ocean depths, and the inertia of water, which cause delays, amplifications, and distortions of the tidal bulges. This model explains the fundamental cause, but local tide predictions require detailed hydrodynamic models.
- Where does the Sun fit into this model?
- The Sun also creates tidal bulges on Earth, but they are about 46% as strong as the lunar bulges due to the Sun's greater distance. The simulator often focuses on the Moon for clarity. When the Sun and Moon align (new and full moon), their tidal forces combine to create higher 'spring tides.' When they are at right angles (first and third quarter), their forces partially cancel, creating lower 'neap tides.'