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Constellations: Draco 'the Dragon'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
Camelopardalis | Cancer | Canes Venatici | Canis Major | Canis Minor | Capricornus | Carina | Cassiopeia | Centaurus
Cepheus | Cetus | Chamæleon | Circinus | Columba | Coma Berenices | Corona Australis | Corona Borealis | Corvus
Crater | Crux | Cygnus | Delphinus | Dorado | Draco | Equuleus | Eridanus | Fornax | Gemini | Grus | Hercules | Horologium
Hydra | Hydrus | Indus | Lacerta | Leo | Leo Minor | Lepus | Libra | Lupus | Lynx | Lyra | Mensa | Microscopium | Monoceros
Musca | Norma | Octans | Ophiuchus | Orion | Pavo | Pegasus | Perseus | Phoenix | Pictor | Pisces | Piscis Austrinus
Puppis | Pyxis | Reticulum | Sagitta | Sagittarius | Scorpius | Sculptor | Scutum | Serpens | Sextans | Taurus
Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula
Draco the dragon, and Ursa Minor.
The dragon wing of night o'erspreads the Earth.
– Achilles – having just killed Hector, sensing impending doom as well as the approaching darkness: Act V, Scene VIII, Troilus and Cressida, by William Shakespeare

The Dragon Constellation

Name:Draco (Latin: 'dragon')
Genitive:Draconis
Short form:Dra
Area:1,083 sq deg
Co-ordinates1:Right Ascension 17h, Declination +65°
Origin:Ancient

Draco 'the dragon' is a Northern Hemisphere constellation which you have to imagine is coiled around the North Pole; you can trace it above the constellations of Ursa Major, Boötes, Hercules, Lyra and Cygnus. It's right next to Cepheus and also shares borders with Ursa Minor and Camelopardalis. Objects of interest include the famous Cat's Eye planetary nebula, the Draco Dwarf Spheroidal galaxy (a satellite of the Milky Way) and the magnificent edge-on Spindle Galaxy.

Mythology

The constellation Draco2 honours the dragon Ladon, who guarded a wedding present from Mother Earth to the goddess Hera and her husband, the great god Zeus. The gift was an apple tree which grew on Mount Atlas and bore golden fruit. One of the 12 labours of Hercules (Herakles) was to steal three of the treasured apples. The only way this could be achieved was by killing the dragon, which Hercules did by firing an arrow over a wall. Hera rewarded the faithful Ladon by placing his image in the sky, marked out with stars.

Dragons

Dragons are mythical creatures who exhale fire. They have been portrayed as friends or a fearsome foe. In the East, they are a symbol of fertility, associated with water and the heavens. Some dragons can be ridden, provided you choose a friendly one, of course. Famous dragon-riders in literature are Atreyu3 and Sparrowhawk4. Famous people other than Hercules who fought with dragons include Harry Potter5, Turin Turambar6, and St George, the Patron Saint of England.

Stars

The scientific star names are simple to understand (if you know your Greek alphabet). For example: 'alpha Draconis' means that it is the brightest star in the constellation Draco. The next brightest is designated 'beta', etc. Combined with the genitive name, this is known as the 'Bayer designation'. Some stars have proper names as well, for example, alpha Draconis is Thuban. Others are known by their catalogue number. With the constellation Draco though, things didn't quite go according to the Greek letter plan, and the brightest star is the orange giant designated gamma, Eltanin, also known as the Zenith Star.

Thuban (alpha Draconis) is the sometime 'pole star' thanks to the wobble of the Earth on its axis, which is known as precession. This is caused by the combined gravitational influences of the Sun and the Moon. When the ancient Egyptians were constructing the Great Pyramid at Giza over 46 centuries ago, they incorporated a small shaft that extended from the King's Chamber to the outside of the pyramid, pointing toward Thuban, which was the pole star of the day.

Star Table

StarDesignationName or
catalogue number
MagnitudeDistance
(light years7)
Spectral classification
and/or comments
α Draalpha DraThuban
(Dragon's tail)
+3.65309White giant
β Drabeta DraAlwaid+2.79360Yellow giant
γ Dragamma DraEltanin+2.23148Orange giant
δ Dradelta DraAltaïs+3.07100Yellow giant
ε Draepsilon DraTyl+3.84147Binary star system
ζ Drazeta DraAldhibah+3.17340Blue-white giant
η Draeta DraAldhibain+2.7488Yellow giant
θ Dratheta Dra13 Dra+4.0168Yellow-white giant
ι Draiota DraEdasich+3.3102Orange giant
κ Drakappa DraKetu+3.85498Blue giant
λ Dralambda DraGianfar+3.82334Red giant
μ Dramu DraArrakis+4.9188Binary star system
ν Dranu DraKuma+4.9899Double star system
ξ Draxi DraGrumium+3.73110Orange giant
σ Drasigma DraAlsafi+4.6818.8Orange dwarf
φ Draphi DraBatentaban Australis+4.22289White giant
χ Drachi DraBatentaban Borealis+3.5526Binary star system
ψ Drapsi DraDziban+4.5772Binary star system

New General Catalogue

The New General Catalogue (NGC) was compiled by John Louis Emil Dreyer (the director of the Armagh Observatory from 1882 to 1916).

Cat's Eye Nebula (NGC 6543)

NGC 6543 was the first planetary nebula to be observed with a spectroscope8. Commonly known as the Cat's Eye Nebula, it has other names such as the Sunflower Nebula and the Snail Nebula. It is awesome to view; through a telescope you'll see a blue-green blob, 3,300 light years distant. There are some spectacular Hubble images - the ones taken in 1994, 1997, 2000, and 2002 can be compared to show just how rapidly the nebula is expanding.

Galaxies

There are several galaxies on view in Draco, of varying types, shapes and sizes. The Spindle Galaxy (NGC 5866) is a spectacular edge-on, which means we view it like we see the rings of Saturn, from the side. The trail surrounding the Knife Edge Galaxy (NGC 5907) was more than likely left by a smaller dwarf galaxy which was eventually absorbed by the larger spiral billions of years ago. The Tadpole Galaxy (UGC 10214) is a distorted spiral whose 'tail' is 280,000 light years long. Lenticular galaxies, (like NGC 5866), are a cross between spirals and ellipticals, with lots of stellar dust giving a 'halo' effect.

Galaxy Table

CatalogueNameTypeMagnitudeDistance
(light years)
Remarks
NGC 4121PGC 38508Elliptical galaxy+14.2UnknownDwarf galaxy
NGC 4125UGC 07118Elliptical galaxy+9.878 millionRecent merger
NGC 4236UGC 07306Spiral galaxy+9.711 millionMember of the M81 group
NGC 5866The Spindle GalaxyLenticular galaxy+9.944 millionEdge-on; Possibly Messier 102
NGC 5907Knife Edge GalaxySpiral galaxy+10.440 millionEdge-on; post merger
UGC 10214The Tadpole GalaxyDistorted spiral+14420 millionOngoing merger
UGC 10822Draco DwarfDwarf galaxy+10.9260,000Discovered in 1954 by Albert Wilson of Lowell Observatory

Extrasolar Planets

There have been many extrasolar planetary systems found in the constellation Draco; the first was discovered in 2001. Figures given in the table below are the length of the planet's orbital period around its parent star, which we know as a year. The mass of the extrasolar planet is compared to that of Jupiter, our Solar System's largest planet, known by astronomers as the 'Jovian scale'.

Extrasolar Planets Table

Star name or
catalogue number
Planet
catalogue number
Planet mass
(Jovian scale)
Orbital period
(Earth days)
Year of discoveryComments
Iota DraIota Draconis b8.95112001First planet discovered orbiting a giant star
TrES-2TrES-2 b1.252.472006Hot gas giant
HD 167042HD 167042 b1.64162007Low eccentricity orbit
42 Dra42 Draconis b3.94802009Gas giant/habitable zone
HD 139357HD 139357 b9.761,1252009Superjovian
Qatar-1Qatar-1 b1.091.422010Hot gas giant
Kepler-4Kepler-4 b0.0773.22010Hot gas giant
Kepler-10Kepler-10 b0.0140.832011Rocky
Kepler-10Kepler-10 c0.06345.32011'Super Earth'
HAT-P-30/WASP-51HAT-P-30/WASP-51 b0.712.812011Hot gas giant
HAT-P-37HAT-P-37 b1.172.82012Hot gas giant

The planet KOI-351 (Kepler-90) has seven planets in orbit, all of which are within Earth-Sun distance.

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (-) for southern ones.2There is no connection with the Athenian lawmaker Draco (from whom we get the word draconian) who believed that misdemeanours such as urinating in public and laziness should be punishable by death.3In The Never-Ending Story.4In The Farthest Shore.5In Harry Potter and the Goblet of Fire.6In The Silmarillion and The Children of Hurin.7A light year is the distance light travels in one year, roughly 5.88 trillion miles or 9.46 trillion km.8A spectroscope is an optical instrument for breaking up light from any source into a spectrum so that it can be studied.

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