Mission 4: The Big DipperAugust 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:
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.
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’.