What happens when you flip your rearview mirror and how does it work to cut the glare?

Who's asking: Tod Goldberg, La Quinta, CA

Did you ever notice that your car's rear-view mirror isn't just a flat piece of glass, but a whole capsule with glass at the front? The glass you see at the front of the rear-view mirror is just that -- clear glass, not really a mirror. The mirror is behind the glass you see, and when you flip the rearview mirror up or down, you adjust the angle of the reflecting surface behind the glass.

If I knew how to draw online, I could show this more easily than words can express it. When the rear-view mirror is in its daytime position, the image of whatever's behind your car bounces directly off the reflecting surface at the back of your rear-view mirror, into your field of vision. When you flip the switch, the reflecting surface tilts so that it's looking at your car's ceiling. Light comes in your back window and passes through the front glass of the rearview mirror, bouncing off the angled reflecting surface at the back of the mirror and then back into your eye -- so the headlights you "see" in the mirror are actually reflections of a reflection, and much dimmer than if you were getting a head-on view or a single reflection.

Aren't optics cool? One of my favorite places in Santa Monica is the Camera Obscura in Palisades Park -- it is open to the public and free, just a big dark room where you can see the outside world reflected on a circular white table in the center of the room.

This is my very first post as a brand-new Mac user -- yes, it's happened, and I am now the proud owner of a gorgeous new MacBook. I feel a little like a newly-shaven Hare Krishna. I promise not to proselytize.