The Apus Constellation

The Apus Constellation.

Apus is a small constellation in the southern sky. It represents a Bird of Paradise, and its name means “without feet” in Greek because the bird of paradise was once wrongly believed to lack feet. First depicted on a celestial globe by Petrus Plancius in 1598, it was charted on a star atlas by Johann Bayer in his 1603 Uranometria. The French explorer and astronomer Nicolas Louis de Lacaille charted and gave the brighter stars their Bayer designations in 1756.

Covering 206.3 square degrees and hence 0.5002% of the sky, Apus ranks 67th of the 88 modern constellations by area. Its position in the Southern Celestial Hemisphere means that the whole constellation is visible to observers south of 7°N. It is bordered by Ara, Triangulum Australe and Circinus to the north, Musca and Chamaeleon to the west, Octans to the south, and Pavo to the east. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is ‘Aps.’ The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of six segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 13h 49.5m and 18h 27.3m, while the declination coordinates are between −67.48° and −83.12°. Best visible in the month of July at around 9.00pm.

NGC 6101

The number of stars that have been catalogued as part of the Hipparcos Star Catalogue from Apus is 701. The nearest star to Earth is HIP 76362 which is roughly about 42.69 Light Years from the Earth. The nearest star to the Earth with an exoplanet is HD 134606 which is about 86.42 Light Years. The furthest star that can be located in the constellation is HIP 73871 which is located about 54360.6 Light Years away from the Sun. Within the constellation’s borders, there are 39 stars brighter than or equal to apparent magnitude 6.5. The five brightest stars are all reddish in hue. Alpha Apodis is an orange giant of spectral type K3III located 447 ± 8 light years away from Earth, with an apparent magnitude of 3.8. It spent much of its life as a blue-white (B-type) main sequence star before expanding, cooling and brightening as it used up its core hydrogen. It has swollen to 48 times the Sun’s diameter, and shines with a luminosity approximately 928 times that of the Sun, with a surface temperature of 4312 K. Beta Apodis is an orange giant 157 ± 2 light years away, with a magnitude of 4.2. It is around 1.84 times as massive as the Sun, with a surface temperature of 4677 K. Gamma Apodis is a yellow giant of spectral type G8III located 156 ± 1 light-years away, with a magnitude of 3.87. It is approximately 63 times as luminous the Sun, with a surface temperature of 5279 K. Delta Apodis is a double star, the two components of which are 103 arcseconds apart and visible through binoculars. Delta is a red giant star of spectral type M4III located 760 ± 30 light years away. It is a semi-regular variable that varies from magnitude +4.66 to +4.87, with pulsations of multiple periods of 68.0, 94.9 and 101.7 days. Delta is an orange giant star of spectral type K3III, located 610 ± 30 light years away, with a magnitude of 5.3.

IC 4499

Two star systems have had exoplanets discovered by doppler spectroscopy, and the substellar companion of a third star system—the sunlike star HD 131664—has since been found to be a brown dwarf with a calculated mass of the companion to 23 times that of Jupiter (minimum of 18 and maximum of 49 Jovian masses). HD 134606 is a yellow sunlike star of spectral type G6IV that has begun expanding and cooling off the main sequence. Three planets orbit it with periods of 12, 59.5 and 459 days, successively larger as they are further away from the star. HD 137388 is another star—of spectral type K2IV—that is cooler than the Sun and has begun cooling off the main sequence. Around 47% as luminous and 88% as massive as the Sun, with 85% of its diameter, it is thought to be around 7.4 ± 3.9 billion years old. It has a planet that is 79 times as massive as the Earth and orbits its sun every 330 days at an average distance of 0.89 astronomical units.

There are no deep space objects that were identified by Charles Messier in this constellation. The Milky Way covers much of the constellation’s area. Of the deep-sky objects in Apus, there are two prominent globular clusters—NGC 6101 and IC 4499—and a large faint nebula that covers several degrees east of Beta and Gamma Apodis. NGC 6101 is a globular cluster of apparent magnitude 9.2 located around 50,000 light-years distant from Earth, which is around 160 light-years across. Around 13 billion years old, it contains a high concentration of massive bright stars known as blue stragglers, thought to be the result of two stars merging. IC 4499 is a loose globular cluster in the medium-far galactic halo; its apparent magnitude is 10.6. The galaxies in the constellation are faint. IC 4633 is a very faint spiral galaxy surrounded by a vast amount of Milky Way line-of-sight integrated flux nebulae—large faint clouds thought to be lit by large numbers of stars. Credits: Constellation Guide, Universe Guide, Wikipedia.

IC 4633 (Right)