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Finding "Up" in our Universe

3-25-11 Milky Way ESO-S. Brunier
The Milky Way Galaxy: Which end is up? Credit: ESO/S. Brunier

The idea of which way is up is very subjective. Depending on where you are on Earth, the stars that you see overhead are going to be different, and not only for your location but also depending on when you are looking.

For Earth, the notion of "up" has come to mean the point above the North Pole, which is where Polaris, the north star, is found. This point is also called the North Celestial Pole. When the Earth spins, it seems like all the stars are circling around this spot in the sky.

Earth and the solar system are not aligned in the same plane. Earth is tilted about 23 degrees from the plane of the solar system, and this is why we have seasons. But this also means that the solar system's "north pole" is not the same as ours. The North Ecliptic Pole is the point in space above the sun about which the rest of the solar system rotates. The North Ecliptic Pole is in the constellation Draco, not far from Polaris and the North Celestial Pole. As you might guess, they are about 23 degrees apart. The constellation of Draco is shaped like a dragon and curls around the bowl of the Little Dipper. The North Ecliptic Pole is found within the first bend between the dragon's head and body.

The Milky Way Galaxy, of which we are also a part, has yet another "north pole" about which the entire galaxy rotates. Just as Earth is not perfectly aligned in the same plane as the solar system, so too are Earth and the solar system not aligned in the same plane as our galaxy. The difference between the galaxy's orientation and our orientation is much larger than that between us and the solar system. To find the point in space that is above the center of the Milky Way Galaxy, you must look below the handle of the Big Dipper. This weekend, look for the Big Dipper in the northeast after sunset. If you make a triangle between the last star in the Big Dipper's handle, the bright star rising above the eastern horizon (Arcturus – remember to arc to Arcturus from the Big Dipper) and the tail star of Leo the Lion (Denebola), the spot in the middle of this triangle is the North Galactic Pole. (Ignore the two bright points of light in the east-southeast –- Saturn and the star Spica below. They are not used in the triangle.) The North Galactic Pole is in the constellation Coma Berenices, just east of the Coma Star Cluster (Melotte 111). As you may have noticed, this point is very close to the Zodiacal constellations of Leo and Virgo. This means that the North Galactic Pole is nearly on the ecliptic, and about 60 degrees from both the North Ecliptic Pole and the North Celestial Pole. Therefore, as you imagine the solar system spinning along inside the arms of the galaxy about the galactic core, you must picture us nearly on our side as we orbit.

-- Kelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She is currently the Feature Writer for Astronomy and Space at Suite101.com. You can follow her on Twitter at twitter.com/Astronomommy.

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