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ELI5 Yahaaa

The tides are not the big one

What If We Had No Moon?

Losing the Moon would cost us a steady lean — a far stranger loss than losing the tide.

With the Moon A steady lean, bigtides, lit nightsWithout it A wandering lean,small tides, blacknights
Only one of these differences would actually matter.

  1. Step 1 of 5

    The tides would shrink, not stop.

    Tide todayMoon plus SunTide with no Moonthe Sun alone
    Smaller, more regular, and still there.

    The Sun raises tides too — about a third as strong as the Moon's. Take the Moon away and the sea still rises and falls twice a day, just far less, and always in step with the Sun instead.

  2. Step 2 of 5

    The nights would go genuinely dark.

    Full MoonBright enoughto cast shadowsHalf MoonEnough to walkbyStarlight onlyShapes, andlittle else
    Lions hunt best on dark nights — attacks on people peak just after a full moon.

    A full Moon is bright enough to read large print by and to cast a shadow. Without it, every night everywhere is as dark as a moonless night is now — which is dark enough that many animals could not hunt.

  3. Step 3 of 5

    The days would be much shorter.

    1 Early Earth:a 6-hour day2 The Moondrags on thetides3 Eachcentury, thespin slows4 Today: 24hours

    The Moon has been braking Earth's spin for four billion years by dragging our tides around. Without that brake, a day would still be somewhere around six to eight hours long, as it was when Earth was young.

  4. Step 4 of 5

    And Earth's lean would wander — this is the real one.

    Earth, held by the Moon Tilt stays near 23°for billions of yearsMars, effectively alone Tilt has swung from0° to over 60°
    A wandering tilt means a climate that never settles.

    Our 23-degree tilt is what makes seasons, and the Moon holds it steady. Alone, Earth would tip and roll over tens of thousands of years, swinging its tilt wildly. Mars, with only two tiny moons, does exactly this.

  5. Step 5 of 5

    So the Moon is a stabiliser, not decoration.

    One large moon A steady lean,for billions ofyears

    The tides are the obvious loss and the smallest one. The thing worth having is four billion years of a climate that stayed roughly put — long enough for something complicated to grow in it.

    How the tide itself works — two bulges, and Earth turning through both — is its own page.

The short version

Without the Moon we would lose small tides and dark nights, but the serious loss is a stable tilt, and therefore stable seasons.

Try it yourself

Spin a top on its own and it wobbles over. Steady it with one finger and it holds its lean. The Moon is the finger.

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