Very nice Flowchart Which Explains It All For You.

(Better to just put a link and boost Wellingtongrey.net's hits than try to reproduce it here since, even if I had RTFM and knew how to do this it would probably be too small to read and everybody would click on the original anyway.)

Consider this your Sunday Science Thread. Comments leaving links to cool Hubble pix, chicken tractors, historical food, historical (VERY historical) globe maps, sustainable energy or other scientifical-related subjects will receive e-lollipops. Enjoy.