You might remember learning about rods and cones in school. They're two types of light-sensitive cells in your eyes. But what your teachers probably didn't tell you is that, in the shade of night, your eyes lie. Rods and cones evolved through activity in daylight, when we're most active. At night, our eyes slack off and tell us to move along, there's nothing to see out there.

Rod cells are sensitive to dim light levels (�scotopic� vision), but they don�t see color. On the other hand, cone cells see colors but they only work in bright light (�photopic� vision). When it comes to seeing in the dark, this combination is like putting eye-poking Curly and Moe in charge of safety. Between the two numbskulls, a brilliant sky filled with colorful stars looks like a dark ceiling with a handful of dim specks. To see in the dark, you need to take control of your inner stooge.

Step outside at night in Whitefish (a small town near Glacier), and you�ll be lucky to count a dozen stars overhead. Stand around in the shadows for 20 minutes and � if a curious cop doesn�t show up first � a couple dozen stars will eventually appear. Glance at your bright cell phone before looking up again, and suddenly you�re back to less than a dozen stars. The same thing happens when you drive into Glacier at night with your headlights on, which I strongly recommend. Wait for 20 minutes in Glacier�s darkness, and you�ll discover at least 3,000 glimmering stars waiting.

This is our ancient night vision � a forgotten skill. Rods and cones use chemicals to convert photons into electrical messages that the brain can understand. But bright light uses up these chemicals faster than our cones can replenish them. We need 20�60 minutes of darkness to refuel our eyes for night viewing. Astronomers and the odd photographer wear red headlamps, not white, because red light doesn�t deplete these eye chemicals or dim our night vision. Red headlamps also have the added feature of making techno-geeks look really, really cool.

We know lots of cool things about rods and cones. But like Larry, the serious stooge, we know a lot less about our third eye.

In addition to rods and cones, we have a third type of light-sensitive cell in our eyes, in our retinas, called retinal ganglion cells (RGC). These microscopic cells have a huge effect when humans and light meet. RGCs regulate the production of melatonin by sending signals to our pineal gland, perched near the middle of our brains like some mysterious portal between two lumpy hemispheres. Our pineal gland, skin and eyes are the only organs that are light sensitive.

-from the tenth chapter, "Night Visions"