Starry Night Software
This sky map shows the location of the double star Nu Draconis in the constellation Draco in the late evening sky in July.
By
updated 7/5/2012 11:56:30 AM ET 2012-07-05T15:56:30

Astronomers who scan the sky nightly with telescopes have found that about one-third of all the stars are double stars. In general, the two components appear to revolve around their common center of gravity, some very slowly, others rather rapidly. Many stars are multiple, some forming double-double stars or even more complex families. 

With summer now officially here, three of the most interesting double stars are currently available in our night sky, high in the eastern sky between 10 p.m. and midnight. They can be readily viewed with good binoculars or better yet, a small telescope.

The following star pairs are three long-time favorites of mine. You may want to try for them yourself on the next clear night.

Celestial headlights
While most folks are familiar with the Big Dipper and Little Dipper, in the same region of the sky is a long, winding group of stars that portrays the mythological creature of a dragon named Draco, which during late evening hours is riding high above Polaris, the North Star

Draco is a very ancient star grouping. The earliest Sumerians considered these stars to represent the dragon Tiamat. Later, the constellation became one of the creatures that Hercules killed.

One of Draco’s tasks was to guard the garden of Hesperides and its golden apples that Hercules was supposed to retrieve. In the stars, Draco coils around Polaris and we now see Hercules standing (albeit upside down) on Draco’s head. [ 10 Night Sky Observing Misconceptions ]

The Dragon’s head is the most conspicuous part of the constellation Draco: an irregular quadrangle in the night sky not quite half the size of the Big Dipper’s bowl. The brightest star is Eltanin, a second magnitude star, shining with an orange tinge. 

Interestingly, a number of temples in ancient Egypt were oriented toward this star. The faintest of the four stars in the quadrangle however is worth looking for: Nu Draconis, a wonderful double star for very small telescopes. 

The two stars are practically the same brightness, both appearing just a trifle brighter than fifth magnitude and separated by just over one arc minute (or about 1/30th the apparent diameter of a full moon). I first stumbled across Nu as a teenager in the Bronx, using low power on a 4 1/4-inch Newtonian reflecting telescope. I likened Nu to a pair of tiny headlights. Check it out for yourself.   

The "double-double" star
Here is a double star that you could almost call Nu Draconis squared.”

Epsilon Lyrae is better known as the “double-double” star. Seeing this object is a test of good eyesight even more severe than that furnished by Mizar and Alcor (the double star located in the middle of the Big Dipper’s handle ). 

Exceptionally good vision on a clear, dark night will reveal Epsilon as undoubtedly two tiny stars (designated Epsilon 1 and Epsilon 2) that are very close together. The separation is 3.5 arc minutes, which is about one-ninth the apparent diameter of the full moon.

  1. Space news from NBCNews.com
    1. KARE
      Teen's space mission fueled by social media

      Science editor Alan Boyle's blog: "Astronaut Abby" is at the controls of a social-media machine that is launching the 15-year-old from Minnesota to Kazakhstan this month for the liftoff of the International Space Station's next crew.

    2. Buzz Aldrin's vision for journey to Mars
    3. Giant black hole may be cooking up meals
    4. Watch a 'ring of fire' solar eclipse online

This feat is probably right at the limit of perfect vision. Binoculars will make the two stars clearly visible. But if you train a small telescope on them, then each of these two stars are themselves shown to be double stars.

Sir William Herschel (1738-1822) was the first to notice them, in 1779. "A very curious double-double star. At first sight it appears double at some considerable distance, and by attending a little we see that each of the stars is a very delicate double star," he wrote.

So here, in what initially might appear as a single speck of light in the sky, we have a system of four stars, revolving intricately about each other. The two stars that make up Epsilon 1 take at least several hundred years or more to orbit each other. An even longer interval of nearly 1,000 years has been assigned to the two stars that make up Epsilon 2. 

Meanwhile, both pairs of stars appear to be revolving about each other and have a common center of gravity with a period that probably is on the order of a million years or more!

Blue and topaz
Without question, this is one of — if not the most — beautiful double stars in the sky. It is Albireo, located in the constellation of Cygnus, the Swan.  It is the star that supposedly marks the swan’s beak. 

A small telescope or even a pair of steadily held binoculars will readily split Albireo into two tiny points of light of beautiful contrasting colors: the brighter one a rich yellowish-orange, the other a deep azure blue, both placed very close together. 

An absolutely stunning view will come with a telescope magnifying between 18 and 30 power. Albireo is believed by astronomers to be a physical pair, although there has never been evidence of any orbital motion between these two colorful stars.

The projected separation between the two is just over 400 billion miles (643 billion kilometers). At least 55 solar systems could be lined-up edge-to-edge, across the space that separates the components of this famous double star.

By the way, there is an interesting rule about the colors of telescopic double stars. If the stars of the pair are equally bright, they have the same color. If they are unequal in brightness, they have different colors. If the brighter star is the redder of the two, as in the case of Albereo, it is a giant star; if it is the bluer, then it belongs in the main sequence of stars along with our sun.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y.

© 2013 Space.com. All rights reserved. More from Space.com.

Photos: Month in Space: January 2014

loading photos...
  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
  1. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  2. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  3. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  4. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

Discuss:

Discussion comments

,

Most active discussions

  1. votes comments
  2. votes comments
  3. votes comments
  4. votes comments