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Right on!! You now have an understanding of what angular
size is, that an object's angular size decreases as it gets further
away, and how you can find the angular size if you know an object's
physical size and its distance.
Of course, you can go the other way and find an object's physical size if
you can measure its angular size and you know its distance. This is often
done in astronomy, since it is straightforward to measure angular sizes by
comparing to objects in the sky whose sizes are known (such as the
Moon...). An object's actual distance is harder to calculate with
certainty, but can often be well-constrained as well. Of course, in
astronomy, we use different units (usually parsecs for distance, arcseconds
for angular size or parallax, and AU for physical size).
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