Models of the Sky - Celestial Sphere We're going to divert for a moment from the discussion of the celestial sphere and all that to talk about angles, sizes and distances. I mentioned that your thumb held at arm's length is about 2° wide. Why did I have to say "held at arm's length"? What happens if you move your thumb really close to your eyes? If you are pretty normal, you'll notice that your thumb looks really big. Does that mean it has a larger angular size? Yes; your thumb's angular size is now larger. What does that actually mean? It means that it covers a larger region of your field of view - it appears bigger. If you could move your thumb further away, it would look smaller - it would have a smaller angular size (basically be less than 2° in size). Is your thumb actually changing its size? No, of course not - not unless you hit it with a hammer during this process. This is all rather cute and silly, but what does this have to do with science and all? Actually, there is a relation between the size of an object, the distance the object is from you and its angular size. The relation between these things is
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.