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Our future, our universe, and other weighty topics


Thursday, July 25, 2013

Visualizing Your Place in the Universe

Visualizing Your Place in the Universe

A few days ago the Cassini space probe orbiting Saturn took an astonishing photograph showing the Earth as a tiny blue dot underneath the rings of Saturn. The photo is shown below.


Photo: NASA/JPL-Caltech/Space Science Institute

Some people have remarked that the image really helps us to keep our little planet in perspective, as it shows Saturn as very large, and our planet as very small. But to get a much better perspective, we must travel much further out in space.

Let's imagine how it would look if you were on a spaceship traveling far, far away from Earth. Let's imagine you are some type of immortal being on a spaceship capable of traveling at 80% of the speed of light.

After twenty or thirty years of travel, you would look out the window of your spacecraft and see something like the image below, assuming you were not looking at the plane of our galaxy. 



You would know that one of those stars was Earth's sun, but you would not be able to detect which star was our sun without checking a computer or an astronomical reference. Our sun would look just like any star in the sky.

The view out your window would look the same way for many hundreds of years. But after thousands of years of travel away from the plane of the Milky Way galaxy, you would eventually be able to see some of the outline of one of the galactic arms of our galaxy. 


Photo: NASA

After finally traveling for tens of thousands of years, you would be able to see our spiral galaxy the Milky Way in all its glory. You might for a moment think of trying to find our sun amidst all of the stars in the Milky Way, but would quickly realize that there was no chance of doing such a thing. Because the galaxy you would see would consist of hundreds of billions of stars, the Sun would be far too small to pick out, as hard as picking out a grain of sand from a giant sand box. 

spiral galaxy
 Photo: NASA

As your lonely voyage reached a length of millions of years, you would be able to see about 54 other galaxies, each a collection of billions or hundreds of millions of stars. These would be the galaxies in the Local Group of galaxies. As you looked out the window, you would see two other spiral galaxies, in addition to the Milky Way: the Andromeda Galaxy and the Triangulum Galaxy. The Andromeda Galaxy would look larger than our Milky Way.

Photo: NASA

Eventually millions of years later the entire Local Group of 54 galaxies would take up only a small part of what you would see in your window. You would also be able to see many other groups of galaxies. 

As your spaceship kept traveling for many millions of years, your ship would pass through countless other clusters of galaxies. You might try to keep track of where your home galaxy the Milky Way was in the sky, but eventually it would become a speck too small to see.

As the length of time of your journey stretched on to hundreds of millions of years, you would wonder: when will I stop seeing galaxy after galaxy? You would remember your own galaxy as the first of millions of galaxies you saw from your window.

Having taken this imaginary trip into space, you may have a clearer idea of how small and microscopic our planet is in the grand cosmic scheme. Our planet Earth is like a mere drop of water in a vast ocean. You and I and the rest of the human race are like bacteria swimming around in that drop of water.

Therefore in all of your thinking, be very, very humble.