Seeing stars

Astronomy and neuroscience are two of the most blogged-about sciences—and the American Museum of Natural History bridged the gap between the disciplines at an event on Tuesday about astronomy and vision.

As Emily Rice, a postdoctoral researcher in the museum’s astrophysics department, explained, when we look at the night sky (especially in areas without serious light pollution), we instantly recognize constellations. The brain is primed to recognize patterns, from the belt of Orion to a friend’s face. Astronomical patterns can be used to navigate the night sky; we can use stars in Ursa Major, for example, to find the North Star.

When we see things we don’t expect to see—like when a New York City resident leaves the bright lights and sees the Milky Way—we come up with more familiar explanations for what we are looking at, maybe thinking at first glance that the Milky Way is a cloud. Our brains are rational, making predictions based on previous experiences about what we will see and testing the predictions against the sensory input.

Every star in the sky—and there are more than 9,000 of them visible to the naked eye at a given time in the clearest conditions—has a color. Unaided, our eyes can make out the colors of only the brightest stars thanks to the workings of our two types of photoreceptors, rods and cones. Rods perceive brightness while cones make out colors, which is difficult in dim light. Our eyes evolved to perceive the relatively small range of wavelengths emitted by the sun. The same is true in the case of other animals, to interesting effect: As red light does not penetrate water, fish can only see blue light.

There are things in the night sky, like the Andromeda galaxy—a galaxy two times larger than the Milky Way and 2.5 million light years away—that are almost imperceptible to the naked eye. But if you use averted vision—looking to the side of the object rather than right at it—the light comes into clearer focus, as the rods are concentrated at the edge of our field of vision.

So when the night is clear and the stars are out, head outside, look up, and put your rods and cones to work.

–Johanna Goldberg

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