Compass (constellation)

Pyxis or the Compass is a constellation in the southern celestial hemisphere. It was introduced in the 18th century by Nicolas-Louis de Lacaille under the name of Pyxis Nautica and is counted among the eighty-eight modern constellations. It is located near the ancient constellation of Argo Navis; in the 19th century John Herschel suggested renaming it Malus, the Mast, but the suggestion fell through. The Compass is fully visible at latitudes further south than 53 degrees North, with February and March being the months with the best visibility.

This constellation is crossed by the Milky Way. Its three brightest stars, Alpha, Beta, and Gamma Pyxidis, are arranged roughly in a line. With a luminosity 22,000 times that of the Sun and 3.68 visual magnitude, Alpha Pyxidis is a blue-white star, the brightest in the constellation. Near Alpha is T Pyxidis, a recurring nova that brightens to magnitude 7 every few decades. Three stars have planetary systems, all of them discovered by Doppler spectroscopy. The Pyxis globular cluster is located about 130,000 light-years away in the galactic halo. This region was not thought to contain globular clusters. The possibility has been raised that this object may have escaped from the Large Magellanic Cloud.

History

In Ancient China the stars Alpha, Beta, and Gamma Pyxidis, along with stars from neighboring Antlia, were part of Tianmiao, a celestial temple in honor of the emperor's ancestors.

The French astronomer Lacaille first described the constellation as La Boussole (the Compass) in 1752, after having observed and cataloged nearly 10,000 stars in the southern skies during his stay in the Cape of Good Hope. He devised fourteen new constellations in the unexplored regions of the southern celestial hemisphere that are not visible from Europe and named them after scientific instruments symbolizing the Enlightenment. Lacaille Latinized the name as Pixis (sic) Nautica in the charts he published in 1763. The ancient Greeks had identified the four main stars of the Compass as the mast of the ship Argos.

The German astronomer Johann Bode established the constellation Lochium Funis (the Log) in 1801 around the constellation of the Compass, but the description did not pan out. In 1844, John Herschel tried to resurrect the classical configuration of Argo Navis by renaming it Malus, the Neck, a suggestion followed by Francis Baily. Later Benjamin Gould restored Lacaille's nomenclature.

Description

The Compass occupies position 65 by covering 220.8 square degrees of night sky (0.535%). Given its position in the southern celestial hemisphere, the entire constellation is visible as far as 52° N latitude, although parts can be seen as far as 72° N. It is bounded on the north by Hydra, on the west by Popa, on the south by Sails, and on the east by the Pneumatic Pump. The three-letter abbreviation adopted by the International Astronomical Union in 1922 is "Pyx". The official boundaries were established by Eugène Delporte in 1930 and delimit an eight-sided polygon. In the celestial coordinate system, right ascensions are between 8h 27.7m and 9h 27.6m, while limiting declinations are −17.41° and −37.29°.

Stars

Main Stars

• α Pyxidis, blue giant of magnitude 3.68, the brightest star of the constellation.
• γ Pyxidis, orange giant of magnitude 4,03.
• XY Pyxidis (HR 3343), 5,74.

Stars with a Bayer name

• β Pyx 3.97; δ Pyx 4.87; ε Pyx 5.59; γ Pyx 4.86; θ Pyx 4.71; θ Pyx 5.24; κ Pyx 4.62; λ Pyx 4.71

Other stars

• Gliese 317, red dwarf containing an extrasolar planet.
• HD 73256 (CS Pyxidis), variable BY Draconis with a "Hot Jupiter" type planet.
• HD 73267, yellow dwarf with an extrasolate planet.
• HD 77361, orange giant "super-rica in lithium".
• HR 3384 (Gliese 309), orange dwarf at some less than 40 light years away.
• Gliese 318, binary white dwarf at about 28 light years.

Planetary systems

Pyxis is home to three stars with confirmed planetary systems, all discovered by Doppler spectroscopy. A hot Jupiter, HD 73256 b, which orbits HD 73256 every 2.55 days, was discovered using the CORALIE spectrograph in 2003. The host star is a yellow G9V-type star that is 69% as luminous as our Sun, the 89% of its diameter and 105% of its mass. About 119 light-years distant, it shines with an apparent magnitude of 8.08 and is about a billion years old. HD 73267 b was discovered with the High-Accuracy Radial Velocity Planet Searcher (HARPS) in 2008. Orbit HD 73267 every 1,260 days, a 7 billion-year-old star of spectral type G5V that is about 89% the mass of the Sun. A red dwarf of spectral type M2.5V that is about 42% of the mass of the Sun. Sun, Gliese 317 is orbited by two gas giant planets. About 50 light-years distant from Earth, it is a good candidate for future searches for more rocky terrestrial planets.

Deep Sky Objects

• NGC 2613, spiral galaxy.
• Open cluster NGC 2627.
• NGC 2818, planetary nebula located near the limit with Sail.