Draco
Written by Tammy Plotner
Located north of the ecliptic plane and a circumpolar constellation for most observers, Draco was one of the original 48 constellations charted by Ptolemy and was later adopted as one of the 88 modern constellations by the International Astronomical Union. This sprawling constellation covers 1083 square degrees of sky, yet only possesses 3 bright stars. The asterism of the "Dragon" is made of up 14 main stars and 75 Bayer/Flamsteed stellar designations reside within Draco's confines. It is bordered by the constellations of Boötes
Hercules, Lyra, Cygnus, Cepheus, Ursa Minor, Camelopardalis and Ursa Major. Draco is easily visible to viewers at latitudes between +90° and ?15° and is best seen at culmination during the month of July.
There are three annual meteor showers associated with Draco – starting with the Delta Draconids. Each year between March 28 and April 7, the Earth begins to pass into the meteoroid stream, and bright streaks will seem to emanate from the sky at a point near the Cepheus border. This meteor shower activity peaks on or near the date of April 7 and the fall rate averages about 5 per hour at maximum. These are known to be very slow meteors, so observe when the constellation is at its highest and watch for long trails! One June 20th, the Delta Draconid meteor shower peaks. These are the offspring of Comet Pons-Winnecke. This time the radiant is more near the handle of the Big Dipper and the fall rate can be anywhere from 10 to 100 meteors per hour on the average. October 9 marks the peak of the annual Draconid meteor shower, the progeny of Comet Giacobinni-Zinner. At times, when this comet has passed near Earth, the fall rate can be spectacular with rates up to 1000 per hour! Its radiant is near Hercules and it is not uncommon even during an "off" year to spot up to 200 meteors per hour during a dark night.
In mythology, Draco the Dragon is well known. To the Egyptians it was a protective goddess whose body was a composite of crocodile, human, lioness, and hippopotamus parts. Perhaps the most famous myth of all depicts Draco as Ladon, the hundred-headed dragon who guarded the golden apples of the Hesperides and one of the labors of Hercules. He lured the dragon to sleep with music so he could steal his apples and Hera place Ladon in the sky as stars in pity. Perhaps Draco is the dragon killed by Cadmus before founding the city of Thebes, Greece – or maybe it's the dragon that guarded the Golden Fleece and was killed by Jason. There's even a Roman legend where Draco was killed by the goddess Minerva and tossed into the sky upon his defeat – as well as the wonderful movie "Dragonslayer" which gave us its own interpretation. No matter which you choose to use, the Dragon is certainly wonderful!
First let's start with binoculars and the brightest star, Alpha, the "a" symbol on our map. Alpha Draconis name is Thuban and this 300 light year distant star has played an important role in our history. At one time, Thuban was a north pole star. Due to the precession of the equinoxes, it moved on… But by 10000 AD, Thuban will gradually move back toward the north celestial pole. In 20346 AD, it will again be the pole star. Of itself, Thuban is a binary star, much too close to be split. It is also a white giant star, more than 250 times more powerful than our Sun.
Turn your attention towards Beta Draconis, the "B" symbol on our map. It's name is Rastaban, which literally means "head of the serpent". Rastaban is a is a G-type supergiant star, and it is also a binary star. It is located about 360 light years from our solar system and if you use a telescope you just might be about to spot the 11.5 magnitude dwarf star companion to this disparate double star!
Now let's take a look at Gamma Draconis – the "Y" shape on our map. Its name is Eltanin, which pretty much means dragon, or serpent. Despite its Bayer designation of "gamma," it is actually the brightest star in Draco, outshining Rastaban by nearly half a stellar magnitude. Right now Eltanin is 148 light years away from us, but the orange giant star won't stay there long. In 1.5 million years, Eltanin will pass within 28 light years of Earth and will become the brightest star in the night sky. I don't think we'll wait up though… It will be awhile.
Off to Psi 1 Draconis – it's the designation that looks like a pitchfork with a 1 beside it. Here we have a great double star! Its traditional name Dziban and the primary of this pair has a nice, slight yellow coloration befitting of it's F-spectral class and it can easily be split with binoculars. Last stop? Omicron… The big "O" on the map. Omicron supergiant star that also has a gravitationally bound companion that can be picked off with small optics. Look for a orange colored primary star and a fainter blue companion. Then you can brag your binoculars were seeing something that was 323 light years away!
Now for the telescope…
One of the best – Best 50, in fact – things to do is planetary nebula NGC 6543 (RA 17h 58.6m Dec. +66 38') – also known as the "Cat's Eye Nebula". This tiny, but bright, planetary is easily seen in a small telescope, but not quite so easily found because of its size and requires high magnification to begin to reveal details and nature. Structurally, it is one of the most complex nebulae known, with high-resolution Hubble Space Telescope observations revealing remarkable structures such as knots, jets and sinewy arc-like features. It was discovered by William Herschel on February 15, 1786, and was the first planetary nebula whose spectrum was investigated by the English amateur astronomer William Huggins in 1864.
Next, try NGC 6503 (RA 17:49.4 Dec +70:09). At around magnitude 10, this spiral galaxy is still suited to fairly small telescopes, even though it could be as far away as 17 million light years. The really cool part about this particular dwarf galaxy is the fact that it is located on the edge of the "Great Void" – a 33 million light year expanse of nothingness between the Hercules, Coma and Local Galaxy Clusters. While it is not completely empty, the void certainly lacks for galaxy clusters and NGC 6503 is one lone customer!
How about looking up NGC 5907 (RA 15h 15m 53.8s Dec +56 19 44)? It was discovered in 1788 by William Herschel and is a member of the NGC 5866 Galaxy Group. This spiral galaxy located approximately 39 million light years away and has a really low metallicity. There are a few detectable giant stars, but it seems to be composed almost entirely of dwarf stars!
Now for NGC 4236 (RA 12h 16m 42.1s Dec +69 27 45). This highly inclined barred spiral galaxy is part of the M81/82 Galaxy Group. Even though it is a low surface brightness, 11th magnitude galaxy, it is not unheard of to be spotted in larger binoculars and small telescopes!
There are many, many more objects in Draco to enjoy, so be sure to get a good star chart and be a "Dragonslayer"!
Charts Courtesy of Your Sky.
Filed under: Astronomy
