Ever felt the walk to your local grocery store or even the dining hall was too long ? Have you ever thought it takes a long time just to visit Boston from Colby ? All these distances and travel times are extremely small when compared to the scale of the universe. The observable universe as we know it stands at roughly 93 billion light years(light years are a measure of the distance light travels in a year) in diameter, but how did we come to this conclusion ?
To answer this it is vital to understand that the universe is expanding. We can observe distant galaxies moving away from earth in all directions. However an important distinction to make is that earth is not at the centre of the universe and all galaxies are moving apart from each other, therefore suggesting an expanding universe. A good visualisation of this is if you take an uninflated balloon and draw dots around the surface of the balloon, after inflating the balloon all the dots are further away from each other. Despite a uniform expansion, dots separated further away from each other travel at a greater speed, this same phenomenon is observed in our universe. 
Picture used from: http://frigg.physastro.mnsu.edu/~eskridge/astr101/kauf28_1.JPG
Using the distance of the galaxies and the expansion rate we have been able to figure out that the universe is roughly 14 billion years old. Due to the expansion of the universe, the universe has expanded over its 14 billion year old life to a current state of roughly 46.5 billion light years in radius or the 93 billion light years in diameter.
The size of the universe can exists on such large scales that it is often hard to comprehend. Take our own solar system: if we shrink the solar system by a factor of 10 billion to 1 then our sun would be the size of a grapefruit, and the earth would only be the tip of a ballpoint pen, furthermore the distance between the sun and the earth would still be over 15 metres and lastly the nearest star object similar to the sun would be all the way in California if the sun was placed here at Colby College. Even after shrinking our very own solar system by a factor of 10 billion the vastness of space is hard to fully comprehend. Even after creating a scale model of 10 billion to one it is not possible to understand the magnitude between galaxies. Thus to grasp the separations that exist in space we can reduce the scale by another factor of 1 billion(scale of 1 to 10^19). At this scale every light year becomes just 1 millimeter and the Milky Way galaxy gets shrunk to roughly 100 metres or approximately the length of a football pitch. Now the distance to our neighbour Alpha Centauri becomes less than the width of your finger and millions of stars would be within the reach of your arms.
Picture taken from: http://i.ebayimg.com/images/g/xeUAAOSw3ydVkUp3/s-l300.jpg
You can follow the link to find out more about the process of figuring out the size of our universe : http://www.bbc.com/earth/story/20160610-it-took-centuries-but-we-now-know-the-size-of-the-universe
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