Models to visualize size and distance in the universe

# JOB 0: Get Started with scales and models

The problem: If each star were represented by a grain of fine sand, How many buckets of sand would it take to represent all the stars of an average galaxy (such as our own Milky Way galaxy)?

 This can be done intuitively The reasoning is this: There must be as many grains of sand as there are stars in the galaxy. Call this number N. Its value is 100 billion. How many times the number of grains of sand in a bucketful is this number? Let the number of grains of sand in a bucketful be called 'n'. The value of 'n' is 1.25 billion. The number of bucketfuls of sand needed is then N/n N/n = [100 billion] / [1.25 billion]    or 80         {Notice that the 'billions' are like units. Only because both the numerator and the denominator are in billions can the 'billions' be cancelled in the ratio.}

 The answer to the question is: 80 bucketfuls of sand have as many grains of sand as the average galaxy has stars.

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