Posts Tagged The Milky Way

Where do we live?

The answer to that question quite obviously relies on the reader, I’m in London for example. You could be in a town nearby, or across the country or for all I know thousands of miles away. But we can group together where we live, if you are reading this in Brighton or Dunstable then we could say we both live in the south of England. If you’re reading this in York or Leicester we could stretch it and say we both live in England. We can play this game for a little while before we inevitably come to the conclusion “we all live on Earth”, but where exactly is that?

Everyone you've ever known is somewhere down there

Our pale blue dot is flinging itself around the campfire we call the Sun at around 30km per second (London to New York in 3 minutes). We share this Sun with seven other planets; Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune along with five dwarf planets; Ceres, Pluto, Haumea, Makemake, and Eris. Along with a few score moons, a couple of asteroid belts and a sprinkling of comets we all make up the solar system together. It’s hard to get round just how big the solar system is, there isn’t even a definitive boundary with clouds of asteroids extending for trillions of kilometres around our Sun. But that number “trillions of kilometres” is meaningless, let’s face it, I could have said billions or zillions for all the connection it has with our lives. In light of this I’d like to share an analogy I often use…

Imagine the distance between the Earth and the Sun (some 150 million kilometres) and shrink it right down to just one metre. At this scale the Earth is just 80 millionths of a metre wide (about the size of ten red blood cells side by side). The Sun is little bigger than a marble at 9 thousandths of a metre. 40cm from the Sun we find Mercury and just 30cm beyond that we have Venus. Within our metre sized orbit the Moon is nearly 2mm from our bacteria sized Earth, about the size of two grains of sand. This is the furthest mankind has ever gone in our universe. It took years for thousands of geniuses and billions of dollars to take us just 2mm on our scale. With the solar system shrunk down like this Neptune, the furthest planet, is just 30 metres away from our marble sized Sun. Eris, the furthest dwarf planet doubles that distance at 62 metres. Taking this orbit as the boundary of our system on our scale a football pitch would fit within our entire solar system with a few metres either side to spare. This is our solar system, over 120 metres wide and the furthest we have travelled is just two measly millimetres. But our home doesn’t stop there.

Our Galaxy viewed from Earth

Our solar system is just one of hundreds of billions inside the galaxy we call the Milky Way. If you live in a place with low light pollution you can look up at night and see the disk of our galaxy cutting straight across the dark. Our spiral galaxy is so large that we have to measure it in lightyears, that’s the distance that light (the fastest possible thing, it travels at 299,792.4 kilometres every second) travels in an entire year! In kilometres that’s 9,450,000,000,000,000! In our scale one lightyear is 61km, nearly twice the length of the English channel at it’s smallest width. The nearest star system to us is four times that again! On our little scale where the Sun is a marble and the Earth just a collection of cells wide the Milky Way is 6 million kilometres wide. Even with our horrendously shrunk down scale the length of the Milky Way is equivalent to circling the equator 200 times. This is our home; our town, our country, Earth, every planet we’ve ever seen all of them are there in this galaxy. But if we are being honest, it’s not really our home. Oh no, we’ve barely begun to talk about that…to be continued.

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