Constellations: Aquila 'the Eagle' Content from the guide to life, the universe and everything

Constellations: Aquila 'the Eagle'

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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
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Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula
Name:Aquila (Latin: 'eagle')
Genitive:Aquilae
Short form:Aql
Area:652 sq deg
Co-ordinates1:Right Ascension 20h, Declination +05°
Origin:Ancient

Aquila, the Eagle, is surrounded by no fewer than nine other constellations that touch its borders. Most prominent are Sagitta that bounds most of its northern flank and Sagittarius its southern. Aquarius is to its east and Serpens Cauda to the west. Aquila is at its most prominent to northern hemisphere observers during midsummer months when its brightest star, Altair forms the southernmost corner of the Summer Triangle with Deneb in Cygnus and Vega in Lyra. The Milky Way is rich in this area of the sky, running diagonally through Aquila. With good viewing conditions, the starfields are a magnificent sight in binoculars or a small telescope on low magnification.

Mythology

Through the ages Aquila has been associated with an eagle in most cultures. In Greek mythology it was the eagle sent by Zeus to retrieve his thunderbolts and to bring the youth Ganymede to Olympus to act as wine bearer for the gods. Aquila's southern stars formerly constituted a separate constellation 'Antinous', named by the Emperor Hadrian in the year 132 AD. Antinous was a favourite servant of the Emperor, who drowned himself in the mistaken belief that to do so would extend his master's life. Hadrian named the constellation after him but it has now fallen into disuse. Another association has been drawn linking Aquila, Cygnus and another defunct constellation, 'Vulcan Cadens', now known as Lyra, with the Stymphalian birds hunted by Hercules in his sixth labour.

Principal Stars

Alpha Aquilae, Altair, is named from the Arabic for the constellation and translates to 'Flying Eagle' or 'The Flying One'. It is the 12th brightest star in the sky at a magnitude of -0.77 and has a very rapid axial spin completing one revolution every 6.5 hours. This causes it to deform into an oblate sphere and distorts its spectral line signature. It is also relatively close to us, at only 17 light-years distance.

Altair is straddled by beta Aquilae, Alshain, and gamma Aquilae, Tarazed, which present a line spanning about five degrees from south-east to north-west portraying the upper body of the eagle. Alshain is 'the Falcon' and Tarazed 'the Plundering Falcon' from parts of the Persian name for the constellation. Together they are occasionally known as 'the Family of Aquila'. Two stars, epsilon and zeta Aquilae, mark the eagle's tail and both have the same name Deneb al Okab, which translates to that part of the bird's anatomy.

Stars

StarDesignationNameMagnitudeDistance (light-years)Remarks
α Aqlalpha AqlAltair (Flying one)-0.771712th brightest star
β Aqlbeta AqlAlshain (Falcon)+3.7149Double star. Red dwarf companion
γ Aqlgamma AqlTarazed (Plundering Falcon)+2.72267Orange giant
η Aqleta AqlBazak (Lightning)+4.1 to +5.31,400Cepheid variable

Clusters and Nebulae

Within Aquila, approximately five degrees south-west of zeta Aquilae, lies a compact, open star cluster NGC 6709. It is some 2,500 light-years distant and contains about 40 stars. Another cluster, NGC 6755, of approximately 100 stars at magnitude +7.5 lies near delta Aquilae. Both clusters are easy objects to find with small instruments.

Contrasting with the starfields of the Milky Way are the dark nebulae of B142 and B143. When viewing conditions are good, they can be seen just over a degree west of gamma Aquilae with binoculars or small telescopes, as dark patches obscuring the stars. B142 has the same angular displacement as that of a full moon and is shaped rather like the Greek letter Epsilon, hence its name the 'E Nebula'.

Clusters and Nebulae

Catalogue NoNameTypeMagnitudeDistance (light-years)Notes
NGC 6709 Open cluster+6.72,50040+ stars
NGC 6751The Glowing Eye NebulaPlanetary nebula+126,500 
NGC 6755 Open cluster+7.56,500100+ stars
NGC 6756 Open cluster+10.716,00020+ stars
B142E NebulaDark NebulaN/A2,000 
B143 Dark NebulaN/A2,000 

Meteor Showers

Two meteor showers occur which have their radiants within Aquila. Evidence of both showers were discovered by radar, which shows the existence of the June Aquilids, occurring between 2 June and 2 July with an hourly rate of between 13 and 35, and the Epsilon Aquilids, during mid-May. Neither shower is prominent.

Novae

On 8 June, 1918, the brightest nova of the 20th Century occurred within Aquila, peaking at magnitude -1.4 near delta Aquilae. It remained visible to the naked eye for some five months afterwards. A second nova2 was recorded on 10 December, 1999, which flared to magnitude 4 but had faded some ten days later.

Extrasolar Planets

It was announced in April 2007 that the hunt for extrasolar planets had found one 2.5 times the mass of our own Jupiter, orbiting a star (HD 192699) in the system's habitable zone. The star is magnitude 6.4 and is at a distance of 220 light years from Earth. The planet orbits its sun in 351.5 Earth days at a distance of approximately 0.78 AU3.

Other extrasolar planet discoveries, including a brown dwarf (failed star), are listed in the table below.

Extrasolar Planets Table

Star name or
catalogue number
Planet
catalogue number
Planet mass
(Jovian scale)
Orbital period
(Earth days)
Year of discoveryComments
HD 192699HD 192699 b2.5351.52007Superjovian
HD 183263HD 183263 b3.69634.232004Superjovian
HD 183263HD 183263 c3.822,9502008Superjovian
HD 192263HD 192263 b0.7224.351999Hot gas giant
HD 179079HD 179079 b0.0814.482009Hot Neptune
VB 10VB 10 b6.4271.52009Superjovian
ksi Aqlksi Aql b2.8136.752008Superjovian
CoRoT-2CoRoT-2 b3.31.742007Hot superjovian
CoRoT-3CoRoT-3 b4.2521.662008Brown dwarf
CoRoT-6CoRoT-6 b3.38.892009Hot superjovian
WASP-80WASP-80 b0.553.072013Hot gas giant

In the Eagle's Talons

Aquila the Eagle has been depicted through the ages with various objects clutched in its talons. Its connections with Zeus have shown it clutching arrows, bows or thunderbolts. One of the later depictions, and probably the most familiar, shows it holding the youth Ganymede4 as he is transported to Mount Olympus.

In July 1969, Apollo 11's Lunar Module, named 'Eagle', dropped out of orbit around the moon and landed on the Mare Tranquillitatis5. The mission badge for Apollo 11 shows an American Bald Eagle, clutching an olive branch in its talons, flying in to a landing on the lunar surface. The badge had been designed by Mike Collins, the third crew-member and the mission's Command Module Pilot. The design had originally shown the eagle carrying the olive branch in its beak and with its legs and claws extended ready for alighting. NASA management rejected that design as appearing to be too hostile and warlike. Collins redrew it with the olive branch in its talons, and this was accepted. Collins commented: 'I hope it drops the olive branch before landing'.

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.2Nova V1494 Aquilae.3AU=Astronomical Unit. One AU is the mean distance that the Earth is from the Sun.4After whom one of the Galilean Moons of Jupiter is named.5The Sea of Tranquillity.

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