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Moon, Pleiades from midnight until dawn September 13-14


Tonight for September 13, 2014

Barbara wrote: “Is there a constellation called the Pleiades? I heard about a winking star in the Pleiades.”

There is a Pleiades, but it isn’t a constellation. Instead, it’s a cluster of stars. Also called the Seven Sisters, this little cluster is part of the constellation Taurus the Bull. It looks like a tiny misty dipper in the night sky. It’s much more dipper-like than the actual Little Dipper in the northern sky.

You can find the Pleiades star cluster easily just by looking for it. No other pattern in the sky is so little and yet so clearly shaped like a dipper. On this September evening, the waning gibbous moon and this star cluster are up in the east late evening or around midnight, or high in the south at or near dawn. (From temperate latitudes south of the equator, the moon and Pleiades rise after midnight and are found in the northern sky around dawn.)

The three medium-bright stars of Orion’s Belt point to reddish Aldebaran. Image Credit: SolarEmpireUK

Before bedtime tonight, or tomorrow before dawn, the moon can guide your eye to the Pleiades. Because of the moonlight glare, however, you might need binoculars to view this cluster tonight. On nights when the moon is out of the sky, you can use Orion’s Belt to find this cluster near the star Aldebaran, the brightest star in the constellation Taurus the Bull.

Pleiades: Famous Seven Sisters

As for the winking … all faint stars are likely to wink out when you look directly at them. The reason is that the light sensitive rods in your eye are found mostly in the outer part of the retina of the eye. That’s in contrast to the color-sensitive cones, which are found mostly in the center of the retina. So when we look directly at something (as we do most of the time), we’re using the part of our eye that is most sensitive to color. But when we look at something indirectly, looking to one side of it rather than directly at it, we’re using the part of our eye that’s most sensitive to faint light.

September 2014 guide to the five visible planets

It’s an old trick in astronomy never to look directly at faint objects. If you look to one side, you can see faint objects better. Astronomers call this trick using your averted vision. Yes, you can see the waning gibbous moon and the Pleiades star cluster (though you might need binoculars) before bedtime this Monday night until Tuesday dawn.

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