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The line the sunlight hits squarely

What Is the Equator?

The equator is an imaginary line, and almost everything about the world's climate is arranged around it.

The whole planet The line halfwaybetween the poles
Nothing is drawn there. Everything depends on it.

  1. Step 1 of 5

    It is simply the widest way round.

    Two poles, where thespin axis comes outOne circle exactlybetween themThe longest way roundEverything elsemeasured from it

    Spin a ball and there is one circle exactly halfway between the two spinning points. On Earth that circle is the equator, and it is the longest way round the planet.

  2. Step 2 of 5

    Sunlight lands squarely there.

    At the equator Light concentrated ona small patchNear the pole The same light spreadthin

    Near the equator the sun is almost overhead, so its light lands concentrated on a small patch. Near the poles the same beam is smeared across a much larger area.

  3. Step 3 of 5

    Which is why the tropics are hot.

    Energy at the equatorConcentrated,year roundEnergy at the poleSpread thin, andgone in winter

    More energy per square metre, all year, with no real winter. That single geometric fact sets up nearly every large pattern in the world's climate.

  4. Step 4 of 5

    Days there stay the same length.

    At the equator Twelve hours oflight, all yearFar north Endless summer light,dark winters

    The equator gets close to twelve hours of daylight every single day of the year. There is no long summer evening and no dark winter afternoon.

  5. Step 5 of 5

    The heat drives the world's winds.

    Air heated and rising Rain falls asit rises andcools Dry air spreads toward the poles It sinks, andmakes deserts

    Hot equatorial air rises, spreads toward the poles, sinks where it cools, and returns. That loop sets where the rainforests are, and where the deserts are.

    Because the Earth bulges at the middle, a mountain top near the equator is the furthest point on the surface from the centre of the planet.

The short version

The equator is the circle halfway between the poles, where sunlight lands most directly, and that fact drives the world's climate.

Try it yourself

Shine a torch straight at a ball, then at its edge. The bright spot and the smeared one are the tropics and the poles.

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