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This rock, hurtling through space

August 17, 2011

Perseid meteor showerImage by Darren Kirby, used via CC license.

We’re nearing the end of the annual Perseid meteor shower, which peaked this past weekend. I caught a few glimpses of it on Saturday night, soaking in my friends’ hot tub after an all-day trail run – but the viewing this year wasn’t as good as usual, on account of the nearly full moon brightening the sky.

Meteor showers are really meaningful to me. It is really easy in our day-to-day life, driving around or sitting in front of our computers, to forget that we are miraculously stuck onto a whirling piece of rock that spins around a giant star in an expanding galaxy, all within a universe that we cannot even begin to understand. Meteor showers are a visible reminder of that connection.

Imagine that you are out in space, somewhere very very far away – so far away that you can view the Earth and the Sun, and all of the inner planets: Mercury and Venus, and on the outside of our planet’s orbit, Mars. Now look at the Earth spinning. You know that the Sun rises in the east and sets in the west – so, in your mental picture, you can visualize which direction the Earth must spin*.

Remember that one complete revolution of the Earth is less than 24 hours (it is actually 23 hours, 56 minutes). This is because the Earth is revolving around the Sun. By the time the Earth has completed one rotation, it has also moved partway along its orbit. Stop and visualize it for a moment: even if the Earth did not rotate on its axis at all, by the time it had revolved around the Sun once (one real year) one “day” (defined as one sunrise and one sunset) still would have occurred. So, the fact that the Earth must spin an extra four minutes to make up what looks to us down here as a full day, means that the direction that the Earth revolves around the Sun must be the same as the direction that it rotates on its axis**.

It takes a bit of effort to wrap your head around this. But I think it’s pretty cool, once you can do that: shift your point of view, look down at yourself and your home planet from outer space, and get a picture of what’s really going on.

And this is what I love about meteor showers. Now that you can think of that connection, of where we are, standing on the surface of this rocky planet that is both spinning on its axis and revolving around the Sun… you can start to see where the meteors, which are simply little pieces of debris from a comet that are drifting in a region of our planet’s orbit, come from. They zoom in from the northeast – just like other celestial bodies, the Sun and the Moon and the stars, which all appear from the east because of how our planet spins.

Meteors are more prevalent in the pre-dawn hours; also because our planet happens to rotate and revolve in the same direction (counter-clockwise). The side of the planet that is turning towards the sun (morning) encounters more meteors than the side that is moving away from the sun (evening). You really need to get that outer-space view going in your head to see that!

I had an experience once that I will never forget – a moment where I literally could feel the planet rotating under me. It was back in the days when I was still working as a geologist. I had been working alone in the Australian outback, doing geological mapping, for several days. I knocked off work for the day and set up camp (which, in the Outback, means parking the Landcruiser at some notable point such as a dried up shrub in the middle of the red dirt). After the sun set, I lay down on the ground under the dead branches of my mulga shrub, my little landmark in the midst of such a huge and flat landscape. The ground was still hot on my back, and somehow that made me feel very connected to the earth, to Planet Earth. The sky was bright over in the west, where the Sun had just set, and as I watched the light fade, I noticed one bright star above me tracking past the mulga branches. And over in the east, a white glow in the sky heralded the rising Moon.

And suddenly I could feel the planet spinning under me, part of me, or me a part of it. I could feel the movement, not of the sky passing above me, but of me and the planet, flying through the sky, through space, me and the planet spinning away from the Sun and towards the Moon. I could almost feel the drag of the atmosphere, almost hear the roar of a planetary wind above me as I spun through space, no longer any separation between Earth and sky, just me and the heat on my back, stuck to this rock and a part of it as we hurtled through space.

So go and enjoy the meteors. Look up to our night sky, and to the Sun and the Moon and the stars and, yes, the meteors. Try to feel how the Earth moves.


*Since the Sun rises in the East, the Earth must spin counter-clockwise (viewed from “above” i.e. the North Pole).
**So the Earth rotates about the Sun in a counter-clockwise direction.

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