Observed on Thursday, August 18, approximately 11:00 CDT
This is the third and final post about my first night of urban skywatching (here are parts one and two). Aside from the M of Cassiopeia and the three stars of the Little Dipper, there was nothing in that particular section of the northern sky that was familiar to me. Yes, there were some very bright stars directly overhead and slightly behind me, but I knew what these were (the Summer Triangle, perhaps the subject of a future post) and I wanted to challenge myself. What could I see in this sparsely populated patch of sky?
I waited a few more minutes in order for my eyes to become even more sensitive to the night. The first pattern I could pick out was a group of four stars (two somewhat bright and two rather faint) forming a little trapezoid far above and to the left of Polaris. Surely, these were all part of a single constellation, but I did not know which one.
Skywatching tip: If you are trying to observe something very faint, don’t look at it straight on. Avert your eyes a bit. This is because your peripheral vision is more sensitive to faint light. So, if something looks faint, look away, and you will see it a little more clearly.
At this point, I was really straining my eyes to find stars. The patch of sky wasn’t completely empty, after all. After waiting and scanning the area again, I counted nine stars between the trapezoid and the Little Dipper. I mentally grouped them into three groups of three and sketched them as best as I could so I could match them up to a star chart later.
I had just about decided to train my eyes upward to the bright stars overhead when—click—our other neighbor’s motion-sensor-activated flood light turned on. Suddenly, it was like closing time at a bar—the silent shame and temporary blindness—and my star show was over.
Later, I discovered that I had found stars in the constellations Draco (the dragon) and Cepheus (mythological king of Ethiopia and husband to Cassiopeia). The little trapezoid of four stars represents Draco’s head. The brightest of the four is Gamma Draconis, or Eltanin; it’s at the top corner of the trapezoid. Moving counterclockwise from Eltanin, the other three stars are Beta Draconis (or Rastaban), Nu Draconis (or Kuma), and Xi Draconis (or Grumium—that’s a fun name). Rastaban is from the Arabic for “head of the serpent,” and it is almost as bright as Eltanin.
See the Log for more information about these stars.
The faintest of the four is Nu Draconis, or Kuma, and it is probably the most interesting. Nu Draconis is a double star, which is what it sounds like: although it appears to be a single point of light to the eye, with binoculars or a telescope, you can actually see that it is two stars. What’s more, astronomers have determined that one of the two stars is also a pair of stars (known as a spectroscopic binary, it can’t be resolved into two stars but we can infer that it is a pair based on the way the light changes). So Nu Draconis is actually three stars in one.
The stars which I had grouped into three groups of three are, according to the star charts, actually a group of five and a group of four. The five stars to the left are also part of Draco. Moving from lower left to upper right, they are Iota Draconis (or Edasich), Eta Draconis (Aldibain), Zeta Draconis (Aldhibah), Chi Draconis, and Delta Draconis (Altais). Aldibain and Aldhibah (Eta and Zeta Draconis) are named for two hyenas or wolves lying in wait in an Arabic story.
The other four stars belong to the constellation of Cepheus. The star at the center of the group, Alpha Cephei or Alderamin, is the brightest. Below Alderamin is Beta Cephei or Alfirk. Above and to the left of Alderamin is Eta Cephei or Al Kidr, and to the right is Zeta Cephei. About 5500 years from now, Alderamin will end up being close enough to the North Pole (due to the precession of Earth’s axis) to serve as the North Star. Beta Cephei, it turns out, is a triple star.
Aside from the trapezoid of Draco’s head, none of these stars really stood out visually for me. Many of these are quite faint; if there are a few clouds in the sky, or you are in a brighter part of the city, they might all disappear. Glimpsing them again will be a challenge, but I imagine it’s a bit like birding. Now that I know where to look, I can spot them again, even though I can never be sure that conditions will be right. Nonetheless, I will certainly look for Draco’s head again and am excited to get my binoculars out on another night and see the two individual stars that make up the Nu Draconis double star.