Beyond Big Dipper, a view outside the galaxy

  • Mike Lynch, Columnist
  • Friday, July 10, 2009 11:46am
  • Life

The Big Dipper is by far the most recognizable pattern in the sky. While it’s not officially one of the 88 constellations we see from Earth, it is the brightest part of a very large constellation known by its Latin name; Ursa Major, which translates into English as the Big Bear.

The Big Dipper is the rear end and tail of the bear. The pot section outlines his derriere and the three handle stars outline his stretched out tail. How his tail got stretched out is part of the tale I’ll tell you in an upcoming Skywatch column.

Every single star in the northwest Washington night sky is part of our home Milky Way Galaxy that is made up of at least a half-trillion stars. The stars we see at a glance are all really close by in a galaxy that’s kind of shaped like a flying saucer with a diameter of 100,000 light-years. Just one light-year equals almost 6 trillion miles.

When we look in the direction of the Big Dipper we’re looking from the thickest plane of our galaxy and more toward the thinner polar regions. That allows us to see outside our galaxy and get a good look at more distant galaxies well beyond the Milky Way.

NASA took advantage of this celestial geography and aimed the Hubble telescope in that direction in space in the very first Hubble Ultra Deep View back in 1995. For 10 consecutive days the Hubble took nearly 350 exposures of that part of the sky. The resulting mosaic photograph showed hundreds of galaxies crammed into a very tiny area of the sky.

In fact if you held a grain of sand at arm’s length that sand grain would cover about the same tiny section of space. Some of the galaxies seen are more than 10 billion light-years away.

With even a moderate backyard telescope you can see at least a handful of galaxies beyond our home stellar turf in and around the Big Dipper. The easiest ones to see are the Bodes Galaxy and the Cigar Galaxy, parked right next to each other above the pot of the Big Dipper.

Both are fairly bright for galaxies and both are about 12 million light-years away, which isn’t all that far on a galactic scale.

The galactic pair is fairly easy to find. Draw a line from the star Phecda on the lower inside corner of the Big Dipper’s pot section to Dubhe on the upper outside corner and extend that line beyond Dubhe about 10 degrees, which is about the distance in the sky between Phecda and Dubhe.

Use lower magnification that will give you a wide field of view and scan that area and you will see two ghostly white puffs. You may even be able to see these galaxies with a good pair of binoculars. Center them in your scope and put in a high magnification eyepiece to see a little more detail.

Bode’s Galaxy, known astronomically as M81, is larger and more circular. It’s a spiral galaxy similar to the Milky Way, but a lot smaller with a diameter of about 35,000 light-years. It’s a lot denser and more crowded than the Milky Way.

The Cigar Galaxy is aptly named since that’s really what it looks like. It’s what astronomers call an irregular galaxy without much organized structure. That’s because the more massive Bode’s Galaxy, just about 150,000 light-years away, has been gravitationally beating up on the Cigar Galaxy for billions of years, leaving it lopsided.

There are two more galaxies to search for near the end of the handle of the Big Dipper. These are the Whirlpool Galaxy, known as M51, and the Pinwheel Galaxy, or M101. These are both larger spiral galaxies. If your telescope is powerful enough you may even see some of the individual spiral arms, but it really has to be a clear sky and you must be away from city lights.

Just below the end of the Big Dipper’s handle is the Whirlpool Galaxy, about 30 million light-years away with a diameter of 75,000 to 100,000 light-years. We have a face-on view of M51 from Earth and that makes the chance of seeing some of the spiral arms a little better. You may also see a little patch of light on one side of the Whirlpool. This is a small companion galaxy known by astronomers as NGC 5195.

A little above the Dipper’s handle, as you can see in the diagram, is the Pinwheel Galaxy or M101. It’s a giant spiral galaxy almost 170,000 light-years in diameter, which is nearly twice the girth of our Milky Way.

Just like the Whirlpool Galaxy we get a face-on look at it which may allow you to faintly see some of the spiral arms.

The Pinwheel Galaxy is more than 27 million light-years distant. If you traveled to M101 in a commercial jetliner at an average speed of 400 mph it would only take you 45 trillion years to get there.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO radio in Minneapolis and is author of the book, “Washington Starwatch,” available at bookstores and at his Web site www.lynchandthestars.com.

The Everett Astronomical Society welcomes new members at www.everettastro.org/.

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