North Pole

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North Pole

The sky offers two north poles. One is the celestial pole. It’s marked by Polaris, the North Star. Earth’s axis aims toward Polaris, so all the stars appear to rotate around it. And the star is in the same position in the sky all day and night — marking due north.

The north galactic pole moves around the sky. It stays in the same constellation, but the constellation turns around Polaris, so the pole moves, too.

This pole is based on the alignment of our home galaxy, the Milky Way.

Astronomers have devised a set of galactic coordinates. The “east-west” line is marked by the plane of the galaxy’s disk. You can get a rough idea of the plane by looking at the hazy band of light that outlines the Milky Way. A lane down the middle of that band generally looks darker than the rest of it — a pretty good marker of the galactic plane.

The east-west coordinates are centered on the heart of the galaxy, in Sagittarius — a galactic longitude of zero. That’s also the starting point for galactic latitude — the position north or south of the plane. The point 90 degrees north marks the north pole. It’s in Coma Berenices. Right now, it’s high in the southeast at nightfall, above the bright yellow-orange star Arcturus.

Since we’re looking away from the Milky Way’s disk, that region offers an unobstructed view beyond the Milky Way. In fact, it’s home to one of the most impressive galaxy clusters around — spreading out near the north galactic pole.

Script by Damond Benningfield

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