1. Introduction

Aquila, a constellation of the northern celestial hemisphere, commands attention with its prominent depiction of an eagle in flight. Situated in the Milky Way, Aquila spans a region of the sky that has fascinated astronomers and stargazers for centuries. Its celestial coordinates lie approximately between right ascension 18h 00m to 20h 30m and declination +0° to +20°, placing it within the realm of the celestial equator (Figure 1).

Figure 1. IAU chart of Aquila. Source: https://www.iau.org/static/archives/images/screen/aql.jpg. Credit: IAU and Sky & Telescope. Reproduced under CC BY 4.0 license.

The name "Aquila" derives from Latin, signifying "eagle," a creature of both symbolic and mythological significance across various cultures throughout history. In Greek mythology, Aquila is associated with the eagle that served as the thunderbolt carrier for Zeus, the king of the gods. The constellation's distinctive shape, resembling an eagle with outstretched wings, has made it a recognizable feature in the night sky and a subject of fascination for astronomers and storytellers alike.

Aquila's celestial prominence extends beyond its mythological associations to its significance in the field of astronomy. Within its boundaries lie numerous notable celestial objects, including stars, star clusters, and nebulae, that contribute to our understanding of the cosmos. Its position along the Milky Way offers astronomers a window into the densest regions of our galaxy, where stars are born, evolve, and interact in dynamic cosmic processes.

Aquila's celestial coordinates also place it in close proximity to other notable constellations, such as Sagittarius, Scorpius, and Cygnus, enriching the tapestry of the northern celestial hemisphere. Its inclusion in the list of 88 modern constellations designated by the International Astronomical Union (IAU) underscores its significance as a celestial landmark and a subject of scientific inquiry.

2. Historical Background

Aquila, the celestial eagle, holds a prominent place in the annals of ancient mythology and cultural lore. Its depiction in the night sky dates back to antiquity, where it played significant roles in the mythologies of diverse civilizations across the globe.

In ancient Mesopotamia, the eagle was associated with the god Enlil, the chief deity of the Sumerian pantheon. Enlil was often depicted as a powerful figure riding on the back of an eagle, symbolizing divine authority and sovereignty over the heavens. The eagle's presence in the celestial sphere likely influenced its subsequent portrayal in other cultures and mythologies.

In Greek mythology, Aquila is closely linked with the figure of Zeus, the king of the gods. According to myth, Zeus transformed into an eagle to abduct the handsome youth Ganymede, whom he desired as his cupbearer on Mount Olympus. The eagle became a symbol of Zeus's power and dominion over the skies, serving as his messenger and companion. The constellation Aquila, with its distinctive shape resembling an eagle in flight, is believed to represent this mythological creature, immortalizing its role in ancient Greek cosmology.

In ancient Egypt, Aquila may have been associated with the deity Horus, often depicted with the head of a falcon or hawk. Horus was revered as a sky god and protector of the pharaoh, embodying the qualities of strength, vigilance, and divine authority. The eagle's presence in the night sky would have been seen as a manifestation of Horus's watchful gaze over the earth, guiding and protecting humanity on its journey through life.

Throughout history, Aquila's depiction as an eagle has resonated with cultures around the world, symbolizing power, freedom, and transcendence. Its position in the celestial hierarchy, soaring high above the terrestrial realm, evokes a sense of awe and wonder in observers, reminding them of humanity's enduring fascination with the heavens and the mysteries they hold.

Today, Aquila remains a prominent feature in the night sky, captivating astronomers and stargazers with its majestic presence and rich mythological heritage. As we gaze upon the constellation's celestial eagle, we are reminded of the enduring legacy of ancient civilizations and their profound connections to the cosmos.

3. Notable Stars in Aquila

3.1. Altair (Alpha Aquilae)

Altair, also known as Alpha Aquilae, is the brightest star in the constellation and one of the brightest stars in the night sky. Classified as a type A7V main-sequence star, Altair shines with a luminosity approximately 10.6 times that of the Sun and lies approximately 16.7 light-years away from Earth. Its name, derived from Arabic, means "the flying eagle," reflecting its prominent position in the constellation and its association with Aquila's mythological imagery.

3.2. Tarazed (Gamma Aquilae)

Tarazed, designated Gamma Aquilae, is another notable star in Aquila. Classified as a red giant, Tarazed exhibits a luminosity approximately 345 times that of the Sun and lies approximately 460 light-years away from our solar system. Its name, derived from Persian, means "the loosed," perhaps alluding to its position as the second-brightest star in the constellation and its role in shaping Aquila's celestial profile.

3.3. Alshain (Beta Aquilae)

Alshain, also known as Beta Aquilae, is a third-magnitude star located in Aquila. Classified as a type A7IV-V subgiant, Alshain shines with a luminosity approximately 18 times that of the Sun and lies approximately 45 light-years away from Earth. Its name, derived from Arabic, means "the falcon," underscoring its association with the celestial eagle and its role in Aquila's mythological narrative.

3.4. Eta Aquilae

Eta Aquilae is a binary star system located in the constellation Aquila. The primary star is a type F8V main-sequence star, while the companion star is a fainter dwarf star. Eta Aquilae shines with a combined luminosity approximately 14 times that of the Sun and lies approximately 128 light-years away from our solar system. Its status as a binary system adds to its astronomical interest and scientific significance.

4. Deep-Sky Objects in Aquila

4.1. NGC 6755

NGC 6755 is a globular cluster located in the constellation Aquila. This spherical congregation of stars contains thousands of individual stars gravitationally bound together. While not as prominent as some other globular clusters, NGC 6755 presents an intriguing sight for observers, particularly those equipped with telescopes capable of resolving its stellar members.

4.2. NGC 6709

NGC 6709 is an open star cluster containing roughly 40 stars, which range in magnitude from 9 to 11. It is about 3000 light-years from Earth. This relatively young cluster consists of dozens of stars of varying brightness and spectral types. 

4.3. NGC 6781

NGC 6781 is a planetary nebula located in Aquila. This glowing shell of gas and dust is the remnant of a dying star shedding its outer layers. NGC 6781's intricate structure and unique morphology make it a fascinating target for astronomers studying the late stages of stellar evolution and the dynamics of planetary nebulae.