Aquila (constellation)

Aquila (the Eagle) is one of the 48 constellations listed by Ptolemy, also mentioned by Eudoxus of Cnidos (century IV BC) and Aratos (III century BC), and currently one of the 88 constellations recognized by the IAU. Ptolemy cataloged nineteen stars together in this constellation and in that of Antinous, the latter arose during the reign of Hadrian (117-138 AD) and which occupied the southern part of the current constellation of Aquila until the beginning of the century XIX, when it was dropped.

Notable features

Aquila constellation

Altair (α Aquilae), the brightest star in the constellation, is a white star of spectral type A7Vn located 16.8 light years away, whose rotation speed at the equator —approximately 286 km/s— is 140 times higher than that of the Sun. This causes it to have a perceptible flattened shape —with a smaller diameter at the poles than at the equator—, the latter having a lower temperature and brightness, a phenomenon known as “gravitational dimming”.

Aquila's second brightest star has very different characteristics, Tarazed (γ Aquilae), a luminous orange giant of type K3II whose diameter is about a hundred times greater than that of the Sun. With almost six times the solar mass, radiates 2500 times more energy than the Sun.

Next in brightness is ζ Aquilae —called Okab—, a white star of the main sequence 83 light-years from Earth; it rotates on itself at high speed -around 320 km/s-, which means that it does not retain its spherical shape either and that it is noticeably flattened at its poles. The fourth brightest star is θ Aquilae, occasionally known by its Chinese name Tseen Foo, a spectroscopic binary with a period of 17.1 days. The two components are a subgiant and a main sequence star whose joint spectral type is B9.5. β Aquilae, named after Alshain, is only the seventh brightest star in Aquila; is a binary composed of a yellow subgiant of type G8IV and a red dwarf, separated by at least 147 au, located 44.7 light-years from Earth.

ξ Aquilae, officially called Libertas, is a yellow giant with an exoplanet. This planet completes an orbit every 136.75 days and is, among the planets discovered in evolved stars, the one with the shortest orbital period. Its mass is at least 2.8 times the mass of Jupiter. Phoenicia, known as HD 192263, is an orange dwarf around which a planet orbits at a distance of 0.15 AU. A planet in orbit around Gliese 752 A, a red dwarf 19 light years away that is part of a binary star system, has also been discovered.

This constellation also contains ZTF J1901+1458, the most massive white dwarf found to date (2021), with 1.35 times the mass of the Sun and a size equal to that of the Moon.

Aquila has several variables of interest, among which η Aquilae stands out, one of the brightest classical Cepheids in the night sky: its magnitude oscillates between 3.48 and 4.39 over a period of 7.1766 days. On the other hand, R Aquilae and W Aquilae are Mira variables: the second is a technetium-rich S-type star whose brightness fluctuates by 7 magnitudes over a period of 490.43 days. 10 Aquilae is a complex variable classified as a fast oscillating Ap (roAp) star, being one of the brightest within this group. Another constellation variable, V605 Aquilae, is the central star of the planetary nebula Abell 50. It is in the final stages of its stellar evolution and is believed to have recently undergone the "final helium flash", spewing recently processed material into the center of the nebula. It currently has a Wolf-Rayet spectral type.

Several important novae have appeared on Aquila. One of them, Nova Aquilae 1918, reached magnitude -0.5, outshining all the stars except Sirius and Canopus.

NGC 6751 planetary nebula (Hubble telescope image)

Aquila contains several planetary nebulae, most notably NGC 6751, in which wind and stellar radiation have created its characteristic ribbon-like features. It is located at an estimated distance of 6,500 light years. By contrast, NGC 6790 is a fairly uniform nebula, both in the visible spectrum and in radio frequencies; its central star is a white dwarf with a temperature of about 73,500 K and a mass equivalent to 0.6 solar masses. A third planetary nebula of interest is NGC 6741, also known as the Ghost Line Nebula, discovered in 1882 by Edward Charles Pickering. It is in a phase of deep recombination that began about 200 years ago. Its central star has a temperature of almost 170,000 K.

Westerhout 43, also known as W43, is a star-forming region in this constellation. Distant 6,000 parsecs, it is considered the most active star-forming region in the Milky Way. Its center contains a dense and massive star cluster with several O-type stars and Wolf-Rayet stars, having been compared to NGC 3603 as well as R136.

W50 is a nebula and possibly a supernova remnant in Aquila. It houses the SS 433 microquasar inside. It is a unique object in that the nebula interacts with the "jets" of the microquasar, located in its geometric center; It is shaped like a spherical shell with two elongated structures called "wings"- W44, another supernova remnant, is one of the few proven cases of interaction between a supernova remnant and a molecular cloud.

Main Stars

Tarazed position (signed in the image) in relation to Altair (in the center)

• α Aquilae (Altair), the twentieth star in brightness with magnitude 0.76 is a white star of the main sequence located at 16.8 light years. Along with Deneb (α Cygni) and Vega (α Lyrae) forms the summer or summer triangle.
• β Aquilae (Alshain), of magnitude 3.71, slightly variable yellow subgigante.
• γ Aquilae (Tarazed or Reda), located 2° north of Altair and second brightest star of constellation with magnitude 2.72.
• δ Aquilae, of magnitude 3,36, double or triple star system whose visible star is a white-yellow subgigante.
• ε Aquilae, star system whose main component is a giant orange star.
• ج Aquilae (Okab or Deneb el Okab), with magnitude 2,99 is the third brightest star of the constellation.
• MIL Aquilae, variable star, one of the most brilliant classic cefeidas, whose magnitude changes from 3.6 to 4.6 in a period of 7,1766 days.
• θ Aquilae, close binary star of magnitude 3,24 whose components are barely separated 0,25 UA.
• ι Aquilae (Al Thalimain Posterior), blue star of magnitude 4,35 distant 307 light years.
• κ Aquilae, a blue giant of magnitude 4.96.
• λ Aquilae (Al Thalimain Prior), 3,42 white-smoothed star located 125 light years.
• μ Aquilae, orange giant of magnitude 4.45.
• Aquilae, a distant supergiant of magnitude 4,69.
• Aquilae (Libertas), a yellow giant with an extrasolar planet orbiting 0.68 AU from it.
• π Aquilae, sixth-scale double star located 3° north of Altair.
• σ Aquilae, eclipsing variable whose shine fluctuates 0.2 magnitudes in 47 hours.
• χ Aquilae, binaria whose components are separated 0.4 seconds of arc.
• ω Aquilae is a Bayer denomination that names two different stars: ω1 Aquilae and ω2 Aquilae, of respective magnitudes 5,28 and 6,02.

Image of W Aquilae with a possible companion obtained with the Hubble telescope

• 10 Aquilae, a complex variable star, one of the most bright Ap stars (roAp).
• 12 Aquilae (i Aquilae), an orange giant of magnitude 4,03.
• 15 Aquilae, a double star; its magnitude 5,40 and 7 components can be solved with a small telescope.
• 19 Aquilae, giant or white-yellow subgiant of magnitude 5.23.
• 31 Aquilae, yellow subgiant of magnitude 5,16 with a high metallicity.
• 35 Aquilae, star Lambda Bootis that is surrounded by a circum-stellar disk of dust.
• 51 Aquilae, white-yellow star of magnitude 5.39.
• 70 Aquilae, bright orange giant of magnitude 4,90.
• Aquilae, variable Mira whose brightness ranges between magnitude 5.5 and 12 over a cycle of 284 days.
• U Aquilae, cefeida whose brightness fluctuates between magnitude 6.08 and 6.86 over a period of 7.0239 days.
• V Aquilae, carbon star and semi-regular variable whose brightness varies between magnitude 6.6 and 8.4.
• W Aquilae, variable Mira whose brightness fluctuates between magnitude 7,3 and 14,3 in a period of 490,43 days.

Animation of images obtained with the Hale telescope over nine years that show the very movement of the two Wolf 1055 components.

• FF Aquilae, a strained variable whose brightness varies between magnitude 5,18 and 5.68 in a period of 4,4709 days.
• OO Aquilae, binaria eclipsante of maximum magnitude 9,20.
• V605 Aquilae (Nova Aquilae 1919), central star of a faint planetary nebula.
• V805 Aquilae, binaria eclipsante of maximum magnitude 7.58.
• V1285 Aquilae (Gliese 735), spectroscopic binary composed of two red dwarfs.
• V1291 Aquilae, variable Alpha2 Canum Venaticorum of average magnitude 5.63.
• V1302 Aquilae, yellow hypergigante star surrounded by several layers of expelled material.
• V1402 Aquilae, hypergigante star and also Be star.
• V1427 Aquilae, another possible yellow hypergigante star, although it can also be a planetary protonebulous.
• V1654 Aquilae (Gliese 775), orange dwarf nearby and variable BY Draconis.
• HD 186104, solar analog of magnitude +7.64.
• Wolf 1055 (Gliese 752), a 19-year-old light binary star composed of two red dwarfs, one of them, known as Van Biesbroeck Star, is one of the faintest known.

Deep Sky Objects

Image of NGC 6741 obtained with the Hubble telescope

• NGC 6709. AR: 18h 51m 30.0s Dec: +10°21'00" (Epoca 2000). Open cluster of about forty stars. Located at 5° of γ Aquilae.
• NGC 6741 or Ghost Blade Nebula, distant planetary nebula about 7000 light years.
• NGC 6751, planetary nebula whose central star has an effective temperature of 140 000 K.
• NGC 6781. AR: 19h 18m 24.0s Dec: +06°33'00" (Epoca 2000). Planetary Nebula 8° southwest of Altair (α Aquilae).
• NGC 6790, planetary nebula that visually presents a uniform look.
• NGC 6803. AR: 19h 31m 18.0s Dec: +10°03'00" (Epoca 2000). Planetary nebula, it looks like a weak disk.
• NGC 6804. AR: 19h 31m 36.0s Dec: +09°13'00" (Epoch 2000) Planetary nebula near the previous one.
• B143, visible dark nebula with large and medium telescopes.
• W43, considered by some authors as the largest star formation region in the Milky Way.
• W49, one of the largest star formation regions in our galaxy, invisible to the optical; W49B is a nebula probably originated by a supernova that exploded over 2900 years ago.
• W44, W50, 3C 391, 3C 397, Kesteven 75, Kesteven 78 and Kesteven 79, supernova remains. W50, distant 5500 paras, houses the SS 433 microquasar, and Kesteven 75 contains the youngest prayer in our galaxy.

Mythology

The constellations of Aquila and Antínoo, the latter not recognized today.

In Greek mythology, the constellation represented the eagle, the only animal capable of flying facing the sun's rays. She was sent by Zeus to take the beautiful young mortal Ganymede to Mount Olympus to serve as a cupbearer to the gods. According to other versions, it was Zeus himself who was transformed into an eagle.

In Hinduism, the constellation Aquila is identified with the half-eagle, half-human deity of Garuda.

Text references

General references

• _ Catasterism (Καταστερισμο).
  • 30: Eagle (;ετός; Aquwin): the eagle who kidnapped Ganimedes, or the one who showed Zeus when he celebrated this a sacrifice before the Titanomaquia, or the eagle in general for having touched Zeus in the casting of birds among the gods.
    • Latin text in Google Books; electronic facsimile.
      • Greek text on the Internet Archive; electronic facsimile.
• HIGINO: Poetry astronomy (Astronomica).
  • 16: Eagle.
    • Italian text.
    • English text on Mary Grant's Theoi site; 1960 trad.