| Arc units in astronomy???
Arc unit refers to the mesurement of length of an arc on the celestial sphere.The one you will hear about most is "arcsecond" or 1/3600 of a degree. If an object exhibits a "parallax shift" of 1 arcsecond, that object is said to be 1 "Parsec" distant, or about 3.26 light years... See link if you want to read more.UPDATE: Saw your additional question. See the link for an in-depth explanation... If you want to see this effect for yourself, do this. Hold you thumb out at arms length in front of your face. Close one eye. Rapidly close one eye and then the other, keeping only one eye open at any one time. You will see your thumb appear to "shift" with relation to distant objects. This is a parallax shift. Since your eyes are a few inches apart, you are viewing your thumb from a slightly different angle from each eye with relation to the background. Hope that helps...
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