To measure astronomical distances, we use a unit of distance called a light year, which is the distance light goes in one year. Light can travel a distance equal to the earth’s circumference in a seventh of a second. The size of the universe is 13.7 billion light years according to recent observations and calculations.

 

When I said this to one of my young daughters, she said she does not know what a billion is. If we use logarithms, it is easier to understand. The logarithm is the number of zeros to write the number. For example, the logarithm of 100 is 2. The logarithm of a billion is 9. The only thing hard about logarithms is that it is a big word! Since we easily understand the number 9, we can understand a billion.

 

The American Museum of Natural History in New York City has a demonstration of planets and other large and small objects, where each object is 10 times as large as the previous object. This demonstration helps understanding the large size of the universe.

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