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Why do astronomers use astronomical units to measure distances in our solar system?
Answer 1:

An astronomical unit is like any other unit: completely arbitrary, but useful. Why do we use a foot? Or a meter? Or an inch? Or a gallon? It's just a useful way of thinking of the sizes of things. So, we have units at all different sizes. It wouldn't make much sense to measure the distance from here to Europe in inches (so we use miles), in the same way it wouldn't be useful to measure the size of an atom using inches (we use a unit called Angstroms Angstroms , which are 0.0000000001 meters). Astronomical units are just a useful way to think about the solar system relative to the distance from Earth to the Sun, because it's easy to use.

For an example of how easy it is, you could either say:
- The Earth is 93000000 miles from the sun, Saturn is 890700000 miles from the sun.
- The Earth is 1AU from the sun, Saturn is 9.6AU from the sun.

When you use AU, it is easier to understand the relative distances, and that Saturn is about ten times farther from the sun.

Answer 2:

The solar system is enormous, and interstellar space is even bigger. One astronomical unit is equal to 150 million kilometers. This makes it much easier to count the distances if they're in counts of Astronomic Units instead of having to count everything in millions or billions of kilometers.


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