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Mission 4: The Big Dipper

August 22, 2009

Mission Objectives: Constellation, Bright Stars, Multiple Stars

Equipment: Naked eye, Binoculars

Required Time: 3 minutes

Instructions: Get to a place with a clear northern horizon, look to the northwest, and find the Big Dipper. Seriously, it’s just that easy. Here, you can practice with this:

The view to the northwest right after sunset in the southern US, in Stellarium.

The view to the northwest right after sunset in the southern US, in Stellarium.

Note the little red W and N in the corners of the picture; at this time of year, the Dipper is exactly halfway between those cardinal points. If you can’t find it, make sure that it’s just after dark, see that your view isn’t blocked by clouds, trees, or mountains, and double check that you are, in fact, in the Northern Hemisphere.

The Big Dipper as a guidepost to the northern sky.

The Big Dipper as a guidepost to the northern sky.

If you can find the Dipper, you can find at least two more bright stars and have an edge on identifying their constellations. The path that is most widely known is that the two stars that make up the front end of the “pan” point unfailingly to Polaris, the North Star, around which everything else in the heavens appears to rotate. Also, you can follow the handle of the Dipper and arc to Arcturus, the brightest star in the constellation Bootes.

Like Lyra, Ursa Major has a double star treat for naked eyes and binoculars. The middle star in the handle is in fact two, Mizar and Alcor, the horse and rider. Your eyes don’t have to be particularly sharp to see that the brighter of the two, Mizar, has a dim companion. This is also a dead easy split with binoculars. A telescope working at even low magnifications of 40-50x will reveal that Mizar has another, even fainter companion, called Mizar B. Mizar was probably the first telescopic binary discovered, possibly as early as 1617, less than a decade after Galileo first aimed a telescope at the heavens. As if all of that weren’t enough, Mizar A and B are themselves both binary, although the components are too close to be separated by telescopes and can only be detected through spectroscopy.  So Mizar is a four-star system, another “double double”, all by itself.

The Big Dipper is just the rear end and oddly long tail of the constellation Ursa Major, the Great Bear. Polaris is at the end of the tail of Ursa Minor, the Little Bear. There are lots of stories about how these bears came to have such long tails–see what you can find. Because Ursa Major is so close to the celestial North Pole,  it is visible for most of the year and only dips below the horizon briefly at mid-northern latitudes. If you go far enough north, the Great Bear is visible all the time. The Greek word for bear is ‘arctos’. And so we call those far northern regions, under the eternal reign of the bear, the ‘arctic’.

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6 comments

  1. Excellent series, Matt! Say, as long as you’re “Arcing to Arcturus”, don’t forget to “Spike to Spica” while you’re at it! 😀

    Tim “Treehopper”
    Faint Fuzzy Weblog


  2. […] Way–only two can be seen easily by most people right now. Those are Ursa Major (including the Big Dipper), which looks good pretty much all the time from the northern latitudes where the BBC offices are, […]


  3. […] emitted at the star’s surface is shifted toward the red. The star has become a red giant. Arcturus in the constellation Bootes and Aldebaran in Taurus are familiar examples, respectively the third […]


  4. […] tried repeatedly through the observing run to bag M51, a spiral galaxy just below the handle of the Big Dipper, but it was too far north, lost in the light dome over Salt Lake City. The big score was picking […]


  5. Really informative, well written and easy to follow. It’s sometimes difficult to share this knowledge in an understandable manner. Could it also be the case that the constellation is in a different position depending on the season and the hemisphere?


  6. Yes – like all of the constellations it circles the celestial pole, and it will appear closer or farther from the horizon depending on latitude, season, and time of night. The best way to understand its motion is to use a planisphere, like this one.



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