Does a Conductor have to know how to play all the instruments in the orchestra/band? Does someone who writes a symphony have to know how to play ALL the instruments for which he writes the music?

Orchestra conductors have always been a mystery to me, Rosie. All they do is wave a baton in the air and then all the musicians inexplicably respond to such an apparently aimless movement by playing a piece of music so perfectly. How do they do it?

 I haven't a clue NP. It looks simple. I mean you and I could get up there and wave a  baton to and fro and I don't think the orchestra would know the difference. They read the music, they play their instruments and what's the conductor doing to facilitate any of that? Maybe keep them together? Maybe they look to him for timing? I'm   hoping someone who knows will respond. Same thing with a composer.  Does he have to know how to play all the instruments for which he writes the music? I mean that's strings and percussion and woodwinds and harps and so forth. When do you learn how to do that? It boggles the mind. Thank you for your reply NP! :)

 Some of the best obstetricians in the world never had the experience of having a baby. I don't know how they managed without all that first hand knowledge.