Pyxis (the Compass) is a small southern constellation introduced by French astronomer Nicolas-Louis de Lacaille during the 18th century. It represents a mariner’s compass, reflecting the importance of navigation during the Age of Exploration.
Although Pyxis lies near the bright star fields of the Milky Way, its principal stars are relatively faint. Its brightest, Alpha Pyxidis, is a hot blue giant shining at magnitude 3.7. The constellation also contains several interesting deep-sky objects, including the colorful planetary nebula NGC 2818 and a distant globular cluster whose origins remain a subject of research.
Where Is Pyxis and When Can You See It?
Pyxis is the 65th-largest constellation, covering approximately 221 square degrees of the southern sky. It borders Antlia, Hydra, Puppis, and Vela. The constellation is best observed from January through March, when it is well placed in the evening sky. It is particularly easy to observe from the Southern Hemisphere, although it is also visible from many northern locations.
To locate Pyxis, begin with Sirius in Canis Major and look southeast toward Puppis. Pyxis lies beyond the brighter star fields of Puppis, forming a relatively inconspicuous pattern of stars. A detailed star chart is useful because none of its stars is especially prominent.
Who Created the Pyxis Constellation?
Pyxis was introduced by Nicolas-Louis de Lacaille, who cataloged the southern sky while observing from the Cape of Good Hope between 1751 and 1753. He originally named it Pyxis Nautica, meaning the mariner’s compass. The name was subsequently shortened to Pyxis. Its position near the former constellation Argo Navis gives it an interesting historical connection to maritime astronomy.
In Greek mythology, Argo Navis represented the ship used by Jason and the Argonauts in their quest for the Golden Fleece. The enormous ancient constellation was eventually divided into three modern constellations: Carina (the Keel), Puppis (the Stern), and Vela (the Sails). Pyxis occupies a neighboring region associated with the old ship figure, but was introduced by Lacaille as a separate constellation.
Notable Stars in Pyxis
Image Credit: Torsten Bronger Alpha Pyxidis – The constellation’s brightest star, a hot blue giant approximately 880 light-years away, shining at magnitude 3.7. It is considerably more massive and luminous than the Sun and has been classified as a possible Beta Cephei-type variable.
- Beta Pyxidis – A luminous yellow evolved star approximately 420 light-years away, with an apparent magnitude of 4.0. It is much larger than the Sun and lies toward the southern part of the constellation.
- Gamma Pyxidis – An orange giant approximately 210 light-years away, shining at magnitude 4.0. It marks the northern portion of the constellation’s principal star pattern.
- Delta Pyxidis – A multiple-star system whose components can be investigated through observations of their relative positions and motions.
- Kappa Pyxidis – A stellar system containing several visually associated components, making it an interesting target for observers studying double stars.
Notable Deep-Sky Objects in Pyxis
Pyxis contains no Messier objects, but several star clusters, galaxies, and nebulae lie within its boundaries.
NGC 2818 — A Colorful Planetary Nebula
NGC 2818 is a planetary nebula approximately 10,000 light-years away, formed when an aging star expelled its outer layers into space. Its intricate structure includes glowing gas shaped by material flowing outward from the central stellar remnant. Hubble Space Telescope images reveal a complex arrangement of filaments and clouds in different colors. These colors trace emissions from different elements and ionization states within the nebula.
NGC 2818 appears against an open star cluster known as NGC 2818A. Astronomers have investigated whether the nebula and cluster are physically associated, an important question because a confirmed association could help establish the age and original mass of the nebula’s central star.
The Pyxis Globular Cluster
The Pyxis globular cluster is a remote collection of old stars situated approximately 130,000 light-years from Earth.
Globular clusters are densely packed, gravitationally bound systems containing large populations of ancient stars. Many orbit in the outer regions of the Milky Way. The Pyxis cluster is especially interesting because its unusual position and motion have prompted suggestions that it may have originated in a smaller galaxy subsequently affected by the Milky Way’s gravity. Researchers have investigated a possible historical connection with the Large Magellanic Cloud, although its precise origin remains uncertain.
NGC 2627 — An Open Star Cluster
NGC 2627 is an open cluster approximately 8,000 light-years away. It contains a loose grouping of stars formed from the same original cloud of gas and dust. Unlike the much denser globular clusters, open clusters are generally more sparsely populated and can gradually disperse over time.
With an apparent magnitude around 8.4, NGC 2627 is beyond naked-eye visibility but can be observed with amateur telescopes under favorable conditions.
NGC 2613 — An Inclined Spiral Galaxy
NGC 2613 is a large spiral galaxy approximately 60 million light-years away. Viewed at a steep angle from Earth, its disk appears elongated, with a bright central region surrounded by darker lanes of interstellar dust. Its apparent magnitude of approximately 10.6 makes it a target for amateur astronomers with suitable telescopes and dark skies.
The galaxy provides an opportunity to observe the structure of a spiral system from a perspective quite different from the face-on galaxies commonly shown in astronomical photographs.