From Websters:

"know: to perceive directly
: to have direct cognition of
: to have understanding of (importance of knowing oneself)
: to recognize the nature of
: DISCERN : to be acquainted or familiar with
: to have experience of
: to be aware of the truth OR [heads up! this is an very important OR!] factuality of
: to have a practical understanding of
: to have sexual intercourse with (archaic)
: to have knowledge
: to be or become cogniznat -- sometimes used interjectionally with you especially as a filler in informal speech

So just to clarify for the pedants here, when I say "I know" (not 'believe' but 'know') the little I do about about astrology, I mean ALL of the above -- except the last one AND the archaic definition (although I confess I've spent quite a bit of quality time between the sheets with my astrology books over the years, in the soft sweet glow of my reading lamp ....   :-)