Understandable Units? You Decide!


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Although it appears small in the sky, the sun is by far the largest object in the solar system. It is also located at an immense distance from the earth- 93 million miles. Can you imagine how long it would take to drive 93 million miles? If you drove at 70 mph and never stopped for food, gas, or rest, it would take 150 years!

Although the sun is a long distance from the earth, most stars are so far away that we cannot measure the vast distances in everyday units. Even though 93 million miles seems like a long distance, the sun is actually very close to the earth compared to some other stars. Such stars as Betelgeuse, Sirius, and Proxima Centauri are so far away that it is difficult to imagine the vast gulf separating us from them.

It would be awkward to express the enormous distance to the stars in miles (But I will). The closest star to us besides out sun is Proxima Centauri, and it is about 25 trillion miles away! But even this mind-boggling distance is only a smidgen of the distance across our galaxy- an outstanding 590,000,000,000,000,000 miles across!!!

These huge distances are easier to understand if measured in units much larger than a mile. One unit that can be used for this job is the light year- the distance light travels in one year. Light travels at a speed of more than 186,000 miles per second- which makes one light year approximately 5.9 trillion miles. Thus the distance across the Milky Way is 100,000 light years, instead of 590 quadrillion miles.

Another way to picture such enormous distances is to compare them with everyday objects. For example, pretend that the period at the end of this sentence was the earth. On this scale, the sun would be reduced to the size of a tennis ball, 19 feet away from the “earth.” The speed of light is now 1/2 an inch per second.

At this scale, we have shrunk the entire solar system down to the size of a baseball stadium or a large parking lot (Still pretty big, right?). How far away do you think the stars would be? You might be surprised to learn that even Proxima Centauri is still a whopping 1,000 miles away! 

But can we apply this size comparison to galaxies? Yes, but the sizes and distances are so large that they are difficult to grasp. Using the same comparison, the Andromeda galaxy (the closest large galaxy to us), would be around 50 million miles across and almost 600 million miles away!

Please comment below with any thoughts or questions.

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