The Earth's strange path through space

Photo of a hurricane from outer space by NASA.
PHOTO: Reuters

The ground we stand on is not as steady as it seems. There are a host of factors that cause the entire Earth to judder and topple

The Earth beneath our feet seems reassuringly solid and unchanging most of the time. But this is an illusion, born of our limited perspective.

Our planet rotates on its axis once every 23 hours, 56 minutes and 4 seconds.

It also orbits the Sun, while our Solar System dashes around the centre of the Milky Way, which is itself hurtling across the Universe towards a region of space called the Great Attractor.

The speeds involved are frankly dizzying.

Even if you ignore all that, the Earth is far from stable. Beneath us, enormous chunks of rock are constantly grinding past each other to make valleys, pushing together to form mountains, or dragging apart to create rivers and oceans.

The ground under us is forever shifting, stretching and wobbling.

Most of the time, this is nothing to worry about. However, our growing understanding of these phenomena is driving a better understanding of the inner workings of our planet.

It is also handy for anyone trying to track and land spacecraft. Here, then, are seven things that make the Earth move for us.

Under pressure

A desktop globe is a perfect sphere, so it spins smoothly around a fixed axis. However, the Earth is not spherical, and the mass within it is both unevenly distributed and prone to moving around.

As a result, the axis around which Earth spins, and the north and south rotational poles at each end of the axis, move about.

What's more, because the rotation axis is different to the figure axis around which its mass is balanced, the Earth wobbles as it spins.

This wobble was predicted by scientists as far back as Isaac Newton. To be more precise, it is made up of a number of distinct wobbles.

Read the full story here

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