Galactic beauty in the Big Dipper
On clear, dry nights - the kind we often see at this time of year in Maryland - it's nice to look up and see familiar constellations. One of the most familiar, of course, is the Big Dipper. The big rectanglular bowl and long, curved handle are easy to pick out in the northern sky at any time of year.
The Big Dipper constellation is also known as Ursa Major, the "Big Bear." The Greeks saw a bear in the pattern, and so did some native North American tribes. The Dipper also has much to offer backyard stargazers.
For example, the star at the bend of the dipper's handle - Mizar - is actually a double star. Its companion is Alcor. They're sometimes used as a test of visual acuity. People with the sharpest eyesight may be able to see two stars there without magnification. For the rest of us, binoculars can easily separate the pair.
The two stars on the side of the bowl farthest from the handle point to the North Star - Polaris - which stands five dipper-heights from the top of the bowl.
You can also use the dipper's handle to find the bright star Arcturus. As the old memory aid says, just "follow the arc [of the handle outward] to Arcturus." Let your eyes trace the handle's arc, continuing beyond the end to the first bright star you come to. That's Arcturus, the third-brightest star in the night sky.
But there's lots we can't see. And there's a striking new image out from astronomers using the Hubble Space Telescope to prove the point. It's a photo of a beautiful spiral galaxy, called NGC 3982. The galaxy is in Ursa Major, 68 million light-years from Earth.
About a third the size of our own Milky Way galaxy, NGC 3982 is 30,000 light-years across, which means it takes 30,000 Earth years for light to travel from one side of the spiral to the other. NGC 3982 is located in a cluster of galaxies, called the M109 Group, located on the lefthand corner of the dipper base.
Here's more on the new Hubble image.
(PHOTOS: Top: NASA. Bottom: NASA/ESA/Hubble Heritage Team/STScI/AURA)