Galaxy cluster Abell 1689, each patch of light is an entire galaxy containing billions, or hundreds of billions of stars.
The Scale of the universe is difficult to comprehend, it is so colossal that the numbers involved are impossible to even imagine. The vast mind boggling distances make the Earth equivalent to a tiny speck of dust in a desert. When you look up at the night sky, that is just a tiny fraction of what is out there.
Most of us go about our daily lives travelling to work, shopping, watching tv, picking the kids up from school, worrying about money, and our minds don’t venture far from the normal day to day routines. Outer space for a lot of people is what’s out there millions of miles away in “space”, but we are actually IN space ourselves on a planet with a very thin protective atmosphere, going around a star, in a Galaxy…in deep space. We are connected to and part of something vast.
We live on a rocky planet orbiting a fairly ordinary star, located on the inside edge of a spiral arm, of an average to large sized galaxy. But in reality our Galaxy the Milky Way is huge, so big in fact that if you stood at one edge of it and shot a laser beam across it, (travelling at light speed…186,000 miles per second), it would take one hundred thousand years to cross it and reach the other side. On a clear night sometimes the Milky Way can be seen as a faint band of light stretching across the sky. This is part of one of the spiral arms, thick with stars, and probably thick with solar systems too. We are looking at it in profile like you would look at a dinner plate edge on. If you could see it face on from interstellar space it would be a spiral, it has 200 billion to 400 billion stars in it. From our view of the night sky we can only ever see 0.000003% of the Milky Way Galaxy.
Our planet orbits our single star among the billions of others. Our single star orbits the Milky Way Galaxy 24,000 to 26,000 light years from the centre, at a speed of 251 kilometres per second. To go round once takes 225 million years (a galactic year), our star has done 20 orbits in it’s lifetime, and 1/250th of an orbit since the evolution of humans.
The Milky Way, an artist's impression
But our Galaxy is not alone, there are countless billions of other galaxies out there, some a lot bigger than the Milky Way. Galaxies group together to form clusters due to the influence of gravity, these clusters can then group together further to form giant galactic super clusters stretching across billions of light years…the largest structures known to mankind in the universe.
So our Sun is just one among billions in our Galaxy, and our Galaxy is just one among billions in the observable universe.
The cosmos is outside mankind, the cosmos doesn’t need the human race. Galaxies have formed, galaxies merge, galaxies get ripped apart, stars are born and stars die, and at this moment other solar systems are in the process of evolving. The winds blow and the sun shines on probably billions of other worlds, and alien flora and fauna could be evolving and thriving in billions of other solar systems. The universe doesn’t need any input from us, it just gets on with it. Beyond our extremely small piece of cosmic real estate in our tiny corner of the universe we have no influence on it whatsoever. In the huge scale of things we are nothing special.
We have been to the Moon and put satellites up around the Earth, we have sent robot landers to the nearby planets, and by now the Voyager Spacecrafts are heading towards intergalactic space. These are all amazing and fantastic achievements, but they are mere baby steps if you look at them from the enormity of our Galaxy and the universe. The Milky Way is one hundred thousand light years from one side to the other, the closest star to the Sun is Alpha Centauri at 4.37 light years away. So if we could build a rocket ship that could travel at 186,000 miles per second (light speed) it would take nearly four and a half years to get there. If the Sun was the size of a full stop on a page, Alpha Centauri would be 10 miles away.
Nearby star systems
If we wanted to travel to the nearest major galaxy that is next to us in intergalactic space, a one way trip would take 2.5 million years travelling at light speed, to get to the Andromeda Galaxy. Light speed is equivalent to a cosmic speed limit and of course radio, tv, mobile phone communications, travel at the same speed. This means we have an expanding bubble of chatter, pictures, music, and data that surrounds the Earth and travels out from us at light speed. So at the very outside we have maybe 80 or 90 years of broadcasts, there are really not that many star systems within 90 light years of us. So when the subject of intelligent alien civilisations comes up, people often say “Well if they exist, where are they and why haven’t they visited us?”. The universe could be literally teaming with life but any intelligent aliens may not even be able to detect us yet, and the distances involved could make travel impossible.
