Draco depicts a dragon, with the creature’s head located just north of the constellation Hercules, and its tail ending between the The Big and Little Dippers in Ursa Major and Ursa Minor respectively. It takes up an area of 1,083 square degrees of the celestial globe, making it the 8th largest constellation in the night sky, and being circumpolar is visible to northern hemisphere observers right through the year. The constellation can also be seen from latitudes as far south as -15 degrees. The brightest star in Draco is an orange giant called Etamin situated 154 light years away and shining with a magnitude of 2.36.
Ursa Major Family of Constellations
Draco is a member of the Ursa Major family of constellations, together with the constellations Coma Berenices, Boötes, Camelopardalis, Canes Venatici, Corona Borealis, Leo Minor, Lynx, Ursa Major and Ursa Minor.
Although Draco has several associated legends, perhaps the most famous is the Greek myth in which it represents Ladon, the dragon tasked by Hera with guarding the golden apples in the Garden of the Hesperides. The apples in the orchard were grown from the wedding gift given to Hera and Zeus by the goddess Gaia, and were said to bestow immortality upon anyone who ate them. For his 11th Labor, Hercales was tasked with stealing three Golden Apples from the fiersome hundred headed dragon that guarded the garden.
Only one meteor shower, the Draconids, is associated with the constellation, and is the result of the Earth travelling through the dust trail left behind by the comet 21 P/ Giacobini-Zinner. The Draconids, which is also sometimes known as the Giacobinids, is active in October, and usually peaks around 7th/8th when 10-20 meteors per hour can be seen. Although this shower is usually described as unspectacular, it does produce the occasional outburst in activity when the Earth passes through the cometary debris stream’s denser regions. In 1933 and 1946, for instance, thousands of meteors per hour were observed, while as recently as 2011 European stargazers witnessed more than 600 meteors per hour.
– Etamin (Gamma Draconis), the constellation’s brightest star, is an orange giant situated 154 light years distant with a visual magnitude of 2.36. It is also referred to as the Zenith star because it lies almost directly overhead as seen from London. Etamin is 72% more massive than the Sun, 471 times more luminous, and may have a red dwarf companion orbitting it at a distance of around 1000 AU. Another notable feature of Etamin is the fact that its proper motion will bring it to within 28 light years of Earth in about 1.5 million years, which will make it as bright as Sirius is today- if we were around to see it. Etamin derives its name from the Arabic for “great serpent”, and can be seen north-north-west of the bright stars Vega in the constellation of Lyra.
– Aldibain (Eta Draconis), the second brightest star in Draco, is a yellow-white giant located 92 light years from our solar system of magnitude 2.73. Aldibain is around 550 million years old, and has about 2.5 times our sun’s mass, but 60 times its luminosity. It is seperated from a physical companion by a distance of 140 AU, which has an orbital period of at least 1,000 years.
– Rastaban (Beta Draconis), the constellation’s third brightest star, is a binary system found 380 light years away with an apparent magnitude of 2.79. Its main component is a yellow supergiant (G2) six times as massive as our sun, 40 times as big, and a spectacular 950 times as bright. The other component is a dwarf star seperated by 450 AU that takes more than 4,000 years to make a complete orbit. Rastaban derives from the Arabic for “the head of the serpent”.
Other notable stars in Dracos includes the blue giants Aldhibah and Kappa Draconis; the white giant Thuban; the yellow giant Altais; the orange giant stars Ed Asich, Grumium and Upsilon Draconis; and the red giant Gianfar. Another interesting star is Kepler-10, which is notable for the fact that it was the first star identified by the Kepler mission as having at least two planets. The first, Kepler-10b, is a small rocky planet that orbits its G-class parent star every 0.8 days, while the second, Kepler-10c, has an orbital period of 42.3 days, placing both planets too close to their parent star to host life. At an estimated age of around 11.9 billion years, Kepler-10 is more than twice as old as the Sun, and at an apparent visual magnitude of 10.69 is invisible without optical aid.
Notable Deep Sky Objects
The most notable deep-sky objects in Draco includes the Cat’s Eye Nebula, and the Tadpole Galaxy, as well as one Messier object called the Spindle Galaxy (M102).
– The Cat’s Eye Nebula (NGC 6543) is a planetary nebula about 3,300 light years distant with an apparent magnitude of 9.8. It is also one of the most complex nebulae ever discovered, with its 11 or more concentric shells of gas and dust having been the subject of intense study over the years. Interestingly, the nebula appears to have formed only in the last thousand years as a result of its central star intermitedly blowing off envelopes of material as it slowly dies. In fact, the powerful solar wind of the central star is blowing off about 20 trillion tons of stellar material per second, which is why the star is now believed to be only a little more massive than the Sun. The star, however, is at least 10,000 times brighter than the Sun.
– Spindle Galaxy (Messier 102, NGC 5866) is a lenticular galaxy found 50 million light-years away that is
70,000 light-years across and contains more than 100 billion stars. When seen edge-on, its shape resembles that of a rod or spindle, hence its name. The actual shape of the galaxy is far from being decided, though, and the presence of a dust ring may suggest it could in fact be a spiral galaxy. It is not certain whether Charles Messier or Pierre Méchain discovered M102 first, but it is certain that William Herschel discovered it independently in 1788.
– Abell 2218 is a galaxy clusters that has the distinction of having being used as a gravitational lens to track down the oldest known object in the universe, a 13-billion year old galaxy that is thought to have formed as soon as 750 million light years after the Big Bang. Abell 2218 is larger than most galactic clusters, and due to its mass of about 10,000 galaxies, the light that passes by it is curved and then refocused in front of it, which is how objects vastly further away become visible. The several arcs in this image is light that was bent by the clusters’ mass, and each arc represents the light from an object behind the cluster, which is only about 2.3 million light years away. The arcs of light in this image, also known as “Einstein Rings”, can be analyzed in the same way that the light from an undistorted image can be analyzed, which is how the oldest known object in the Universe was identified.
– Tadpole Galaxy (Arp 188) is a barred spiral galaxy 400 million light years away wih a magnitude of 14.4. The galaxy contains numerous clusters of young blue stars, and gets its name from the long tail of stars that stretches around 280,000 light years from the main galaxy.