A coincidence of units makes interstellar distances easy to visualize. One light-year is ≈63,240 AU. One mile is 63,360 inches. So if Earth was an inch from Sol

A coincidence of units makes interstellar distances easy to visualize. One light-year is ≈63,240 AU. One mile is 63,360 inches. So if Earth was an inch from Sol, Alpha Centauri would be four miles away. Voyager probes would be 100-ish inches away, traveling about 3 inches per year. This also gives you some idea of how tiny parallax[1] is. Parallax to Alpha Centauri is equivalent to looking at something four miles away and moving your head two inches. This is where the parsec comes from. If moving 1 AU causes an object to have an arc-second of parallax, that means it's 3.26 light-years away. An arc-second is a tiny angle. There are 360 degrees in a circle, 60 arc-minutes in a degree, and 60 arc-seconds in an arc-minute. To give you another point of reference, an arc-minute would be about an inch separation at 100 yards. Current instruments can use parallax to measure distances up to 300 light-years. The Gaia mission should be able to measure angles as small as 20 millionths of an arc-second.[2] 1. https://en.wikipedia.org/wiki/Stellar_parallax https://en.wikipedia.org/wiki/Stellar_parallax 2. https://en.wikipedia.org/wiki/Gaia_(spacecraft) https://en.wikipedia.org/wiki/Gaia_(spacecraft)