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North Galactic Pole

April 12, 2014

Our home galaxy, the Milky Way, is shaped like a giant pancake. On dark nights, away from city lights, you can see the outline of that disk as the hazy band of light known as the Milky Way. Tonight, with the help of a bright star, you can gaze straight up and out of the disk — deep into intergalactic space.

One of the two points where we look perpendicular to the Milky Way's starry disk is called the north galactic pole. It has nothing to do with the North Star, which is above Earth's north pole, marking the north celestial pole.

Unfortunately, no bright star marks the galactic pole, which is in the faint constellation Coma Berenices. But you can still find the galactic pole’s rough position thanks to the bright orange star Arcturus.

Arcturus is the fourth-brightest star in the night sky. Look for it in the east as night falls. If you need help finding it, just look for the Big Dipper. Follow the curve of the dipper’s handle away from the bowl, and you’ll “arc to Arcturus.”

Now, to find the north galactic pole, look just a little to the west of Arcturus. There, you’ll be gazing nearly straight out of the Milky Way’s disk of stars, into a universe of galaxies. In fact, the two best-known galaxy clusters — the Virgo cluster and the Coma cluster — lie quite close to the galactic pole, so this part of the sky often attracts astronomers who study galaxies beyond our own.

Tomorrow: getting ready for a lunar eclipse.


Script by Ken Croswell, Copyright 2014

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