Some Light Science Reading. The Constellations: Draco

As first appeared in the May 2012 edition of the Syracuse Astronomical Society newsletter The Astronomical Chronicle.


Image generated with Starry Night Pro 6.

We return to our circumpolar constellation discussion begun with the Jan/Feb/March 2012 issue (our first “quarterly” report) by scaling up the Northern Horizon towards Draco the Dragon.

Draco, like all reptiles, is a bit on the dim side. Most of its constituent stars are in the 3 to 4.5 Magnitude range, making it an easy target in dark skies but a bit of a hunt near larger cities. If you’ve never looked for it before, it rivals Ursa Minor (the Little Dipper) in terms of “meh” apparent brightness in the sky (so it is far less pronounced than the Big Dipper or Cassiopeia, the two most prominent Constellations in this part of the sky).

Your best bet for identifying the stars in Draco may be to start right at the head and work your way down (and around, then over, then up, then way over the other way). One of my recent discoveries is that the head of Draco is, itself, a noted asterism (or noteworthy arrangement of stars that are not of the proper 88 Constellations) referred to as “The Lozenge” (“1” in the image above). I had been subconsciously thinking of Monty Python references to throw into this article and realized that saying “The Lozenge” several in a low John Cleese voice a la “The Larch” just about does it. The head of Draco is made from the brightest stars in the Constellation and does make for a reasonably easy target, as it sits between the two bright stars of the Little Dipper’s bowl (“2” In the image at right) and Vega (“3”), the ridiculously bright star making its triumphant return to Spring skies (if you’re at Darling Hill near sunset, you will see Vega as one of the first stars to appear above the Eastern Horizon well before it gets really dark). For those of you familiar with the Keystone (another famed asterism) that makes up the torso of Hercules (“4” in the image above), simply drive your eyes to the left-ish during the early night.

The historical origins of Draco as a lizard of any kind are localized to the Mediterranean, and these origins go back far enough that Draco is one of the Almagest’s Original 48. The Greeks, and so the Romans, saw Draco as a Dragon (or, at least, lizard) of generally ill repute. Draco was seen by the Greeks as a guard of Hesperides’ golden apples and/or a guard (or target, depending on how you read the sentence) of Jason’s mythical golden fleece. The Romans saw Draco as the remains of the dragon killed by their goddess Minerva. It is perhaps fitting that, if you imagine Ursa Minor (the Little Dipper) as an ax on a questionably straight handle, then Draco is precariously on the celestial chopping block preparing to be cleft in twain.

The body of Draco is a healthy mix of single and double stars. In the boring single star category are Giausar, Thuban, and Nodus I. The double star list includes Edasich, Aldhibain, Altais, Rastaban (“eh mahn!”), Eltanin, and Grumium.

Thuban is one star in Draco to spend a bit of time on. In fact, it’s one to spend several thousand years on. As late as 2700 B.C.E., Thuban held the place of Polaris as our North Star. The Earth may seem reasonably unchanging with respect to the seemingly unchanging arrangement of stars of our 100-year-ish lifetimes, but on the geological or cosmological timescales our Earth is as dynamic and fast-moving as that famed clay dreidel. The 26,000-year cycle we know as the precession of the equinoxes (shown above) is one of those processes that requires nearly the entire history of what we know as civilization to mark significant timespans for, but it is reported in several places that Thuban was of significance to the Egyptians in their building of the pyramids over 5 millennia ago (I would be happy to report that Thuban was the North Star that the main shaft of the great pyramid of Cheops was aligned to, but I’ve found conflicting reports online from otherwise reputable locations, so will simply report that the Egyptians very likely knew that this star appeared to move far less over the course of the night than any other and, therefore, held it with great regard).

For those observing at Darling Hill or anywhere south of Syracuse, Draco is a tough reptile to sustain one’s astronomical appetite on. At least two comets are currently passing through Draco at the moment. One, LINEAR (C/2011 F1), is just off the Spindle Galaxy M102 (we’ll come back to that) and, at 3 a.u. and closing, may improve beyond its apparent magnitude of 12.5. Draco also hosts Garradd (C/2008 P1) far beyond its tail star. At an apparent magnitude of 21.30, you have absolutely NO chance of seeing this comet from Darling Hill.

Draco is regrettably light on deep sky objects as well. The local color (at about 3400 light year) is provided by NGC 6543, known as the Cat’s Eye Nebula (above). This is regarded as one of the most structurally complex nebulae in the Night Sky, although this complexity is only revealed through astrophotographic studies. NGC 5866 (below), also known as the Spindle Galaxy (which is very likely Messier 102, although some debate exists), is one of the great photographic sights in astronomy to my eyes. This edge-on galaxy view produces amazing density of material and spindly, fibrous clouds of dust and stars along the plane of the galaxy and a bright glow of stars all around this dense, dark line.

Now, the long curving body of Draco and its positions near the North Star does afford it one benefit in the Northern Horizon. Satellites! There are many bright (brighter than magnitude 4.0) satellites that follow paths over the Earth’s poles, meaning those Constellations near the North and South poles are constantly getting pierced by manmade weather, communications, and “other” satellites. Simply letting my copy of Starry Night Pro go at high-speed with Draco at the center reveals over a dozen of these satellites over the course of just a few hours.

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