The Moon Holds the Axis Steady
Cosmology · · 6 min read · By No Design Editorial
Our tilt gives us seasons. Without a large moon anchoring it, that tilt would wander, and Mars shows what happens to a world when it does.
Earth's axis leans by roughly twenty-three and a half degrees. That tilt is why you get seasons rather than a uniform year, and why the climate at a given latitude stays within a range life can plan around.
The tilt does not hold itself steady. The astronomer Jacques Laskar and colleagues showed through long-term simulations that a large moon anchors it. Without that anchoring, the tilt would wander chaotically over millions of years.
Mars is the demonstration, and it is a useful one because it is not hypothetical. Mars has no large moon, and its axis swings widely enough to drive climate instability that no stable biosphere could ride out.
There is a related point about the tides that is often stated loosely. Tidal force does not fall off with the square of distance, as gravity does, but with the cube. That is why the moon, small and near, raises larger tides than the sun, which is vastly more massive but far away. The arithmetic runs on cubes, and it is worth getting right.
One caution belongs here, because it is the discipline this chapter is built on. Explaining the mechanism is not the same as explaining the setting. Showing how a moon stabilises an axis tells you how the system behaves. It does not tell you why the value sits where a biosphere needs it. Mechanism is not calibration.
From Chapter 10: The Nearer Sky.
Tags: Moon, Tides, Climate, Quran