Pyxis
“The Compass” · Southern · best around March evenings
Real star positions and magnitudes (HYG database via D3-Celestial, BSD-3). Lines are the conventional stick figure; north is up.
The story
Lacaille's magnetic compass, set beside the old ship's hull. T Pyxidis, a recurrent nova, erupts here every few decades.
How to find it
East of Puppis.
✦ What lives inside it
- T Pyxidis recurrent nova
The deep dive
Researched for the Atlas from Wikipedia — Pyxis (12,018 characters read) · updated Sep 20, 2026
01 A Compass Born from a Cape of Good Hope
Nicolas-Louis de Lacaille didn't invent Pyxis from an armchair in Paris. He earned it by spending two years at the Cape of Good Hope, where he personally observed and catalogued nearly 10,000 southern stars — a staggering feat for an 18th-century astronomer working by eye and candlelight. From that data he devised fourteen new constellations in the uncharted southern sky, filling gaps invisible from Europe. He first described the constellation in French as la Boussole, meaning simply "the Marine Compass," in 1752. By 1763 his published chart Latinised the name to Pixis Nautica — the misspelling of Pyxis is preserved in the historical record. Thirteen of his fourteen new constellations honoured instruments of the Age of Enlightenment: telescopes, microscopes, furnaces, and the like. Pyxis fits that theme perfectly, representing the magnetic compass a ship's navigator would have used to steer by. The choice was deliberate: Lacaille placed his compass near the stars of the old ship Argo Navis, so a mariner's tool sat alongside the most famous ship in classical mythology.
02 The Mast That Almost Replaced the Compass
Pyxis has worn more than one name. The Ancient Greeks had already looked at its four main stars and seen not a compass but the mast of Jason's ship, Argo Navis. When John Herschel revisited the region in 1844 he tried to revive that classical reading, proposing to rename the constellation Malus, the Latin word for a ship's mast, as part of a broader attempt to resurrect the classical configuration of Argo Navis. Francis Baily followed Herschel's suggestion, and for a time the name had real currency: old catalogs of the United States Naval Observatory list Alpha Pyxidis as α Mali, star 3766 on page 97. But Benjamin Gould stepped in and restored Lacaille's nomenclature, and the International Astronomical Union's 1922 adoption of "Pyx" as the official three-letter abbreviation settled the matter permanently. Earlier still, German astronomer Johann Bode had tried something different, defining a constellation called Lochium Funis — the Log and Line, a nautical device once used for measuring a ship's speed and distance at sea — around the same stars in his 1801 atlas. That depiction never caught on either.
03 Ancestors of the Emperor, Written in Stars
Long before Lacaille pointed his instruments southward, astronomers in China had already woven these stars into their own celestial architecture. In ancient Chinese astronomy, Alpha, Beta, and Gamma Pyxidis were grouped together with stars from the neighbouring constellation Antlia to form an asterism called Tianmiao — a celestial temple dedicated to honouring the ancestors of the emperor. The name carries deep ceremonial weight: ancestor veneration was central to Chinese court culture, and projecting a sacred temple into the sky elevated that practice into the cosmic order. This stands in sharp contrast to the Western tradition, which saw the same stars as navigational hardware — first a mast, then a compass. Neither reading is more correct than the other; they simply reflect the priorities of the societies that made them. The Chinese asterism is a reminder that faint, easily overlooked constellations like Pyxis still carried cultural meaning across many traditions, even when they contained no spectacular first-magnitude beacons to draw the eye.
04 Alpha Pyxidis: Dimmed by Dust Deeper
At magnitude 3.68, Alpha Pyxidis is the constellation's brightest star, but it is being shortchanged by the universe. Interstellar dust along the line of sight dims its light by 30 percent; without that obscuration it would shine at magnitude 3.31. It is a blue-white giant of spectral type B1.5III located 880 ± 30 light-years from Earth, and it pours out around 22,000 times the Sun's luminosity — roughly the combined output of twenty-two thousand suns stacked together. Its diameter is 9.4 ± 0.7 times that of the Sun, and it began life about 15 million years ago with a starting mass of 12.1 ± 0.6 solar masses. That birth mass matters: stars much heavier than about eight solar masses are destined to end as supernovae, and at 12 solar masses Alpha Pyxidis sits well into that territory. Beta Pyxidis, the second brightest at magnitude 3.97, tells a very different story: a yellow bright giant or supergiant of spectral type G7Ib-II, it lies only 420 ± 10 light-years away and shines at around 435 solar luminosities, with a faint magnitude-12.5 companion separated by 9 arcseconds.
05 T Pyxidis: A Star That Explodes on Schedule
About 4 degrees northeast of Alpha Pyxidis lurks one of the sky's most reliably dramatic variables. T Pyxidis is a recurrent nova — a binary system in which a white dwarf of about 0.8 solar masses and a red dwarf companion orbit each other every 1.8 hours, a pace so fast the pair completes a full orbit in roughly the time it takes to watch two films. The white dwarf steadily accretes material from its companion until the accumulated hydrogen ignites in a thermonuclear runaway on its surface. The result is a violent brightening: T Pyxidis has surged from its baseline of around 14th magnitude up to 7th magnitude — becoming roughly 630 times brighter — in the years 1890, 1902, 1920, 1944, 1966, and most recently 2011. That is six recorded outbursts across little more than a century. The system lies approximately 15,500 light-years from Earth, meaning each explosion we observe actually happened thousands of years before we detect it. As recurrent novae go, T Pyxidis is unusually well-documented, making it a favourite target for researchers tracking how such systems evolve between eruptions.
06 A Globular Cluster Far Outside Its Expected Home Deeper
Discovered in 1995, the Pyxis globular cluster sits roughly 130,000 light-years from Earth and about 133,000 light-years from the galactic centre — placing it deep in the galactic halo, a region not previously thought to harbour globular clusters. Its age has been measured at 13.3 ± 1.3 billion years, making it nearly as old as the universe itself. What makes it scientifically provocative is its location and orientation: it lies on the same plane as the Large Magellanic Cloud, a satellite galaxy of the Milky Way roughly 160,000 light-years away. This geometric coincidence has led researchers to raise the possibility that the Pyxis cluster is an escaped object — a globular cluster that once belonged to the Large Magellanic Cloud and was stripped away, wandering into the Milky Way's halo. If confirmed, it would join a small but growing catalogue of objects whose apparent membership in our galaxy masks a history of capture from elsewhere. The question remains open, and the cluster continues to attract attention precisely because it challenges simple assumptions about where such ancient stellar cities can form and survive.
07 Theta Pyxidis: A Giant Still Growing Deeper
Among the more unusual stars in Pyxis is Theta Pyxidis, a red giant of spectral type M1III that has expanded to approximately 54 times the diameter of the Sun. To put that in perspective, if placed at the centre of our solar system it would engulf Mercury and approach Venus. It is a semi-regular variable, meaning its brightness fluctuates without keeping strict time: researchers have measured two distinct periods of 13 and 98.3 days, suggesting that multiple pulsation modes are operating simultaneously within the star's outer layers. Its average magnitude sits at 4.71, placing it at the edge of naked-eye visibility under good conditions. Kappa Pyxidis offers a useful comparison: another orange giant, spectral type K4/K5III, it shines at magnitude 4.62 from a distance of 560 ± 50 light-years and carries a luminosity of approximately 965 solar luminosities. Kappa was catalogued by Lacaille but initially denied a Bayer Greek-letter designation; it was Benjamin Gould who later judged it bright enough to deserve one. It has a magnitude-10 companion separated by 2.1 arcseconds, a challenging split even for a moderate telescope.
08 Binary Stars That Stretch, Pulse, and X-Ray the Sky Deeper
Pyxis turns out to be unusually rich in interacting binary systems. TY Pyxidis is an eclipsing binary whose two nearly identical G5IV stars — each 2.2 times the Sun's diameter and 1.2 times its mass — orbit each other every 3.2 days, producing magnitude swings between 6.85 and 7.5. Classified as an RS Canum Venaticorum variable, the system is notable for prominent starspot activity and emits detectable X-rays; analysing how that X-ray emission varies over time led researchers to conclude that a loop of material physically arcs between the two stars, 184 ± 5 light-years from Earth. XX Pyxidis adds another layer of complexity: its primary is a white main-sequence A4V star of 1.85 ± 0.05 solar masses, a Delta Scuti pulsating variable studied as a tool for astroseismology. Its companion, probably an M3V red dwarf of about 0.3 solar masses, orbits so close that the gap between them may be only three times the Sun's diameter — the gravitational tide deforms the brighter star into an egg shape. That deformation was itself a clue that helped astronomers make sense of what had seemed like irregular pulsations in an otherwise well-behaved class of variable star.
09 Henize 2-10: A Dwarf Galaxy With a Heavyweight Core
Thirty million light-years away in the direction of Pyxis lies Henize 2-10, a dwarf galaxy that punches well above its size class. At its centre sits a black hole of around one million solar masses — a million times the mass of the Sun compressed into a region smaller than our solar system. The galaxy is classified as a starburst galaxy because it forms new stars at an exceptionally high rate, and that vigorous star formation gives Henize 2-10 a distinctly bluish colour: the sky is packed with massive, hot, young stars that radiate intensely in blue and ultraviolet light. Dwarf starburst galaxies like this one are of particular interest to cosmologists because they may resemble the small, furiously star-forming galaxies that were common in the early universe, contributing to the build-up of stellar mass across cosmic time. The presence of a million-solar-mass black hole in such a small system also raises questions about how central black holes and their host galaxies influence each other's growth — a relationship researchers are still working to untangle.
10 Three Planetary Systems Found by Wobble
Every confirmed exoplanet in Pyxis was found the same way: Doppler spectroscopy, sometimes called the radial-velocity or wobble method, which detects the tiny back-and-forth motion a planet induces in its host star's light. HD 73256 b was the first, found in 2003 using the CORALIE spectrograph. It is a hot Jupiter that sweeps around its host — a G9V yellow star of magnitude 8.08 about 119 light-years away — in just 2.55 days. HD 73267 b followed in 2008, discovered with the High Accuracy Radial Velocity Planet Searcher (HARPS); it takes 1,260 days to complete one orbit around a 7-billion-year-old G5V star. The third planetary host is Gliese 317, a red dwarf of spectral type M2.5V with about 42 percent of the Sun's mass, roughly 50 light-years from Earth. It is orbited by two gas giant planets and has been singled out as a good candidate for future searches for smaller, rocky, terrestrial-type planets. All three discoveries illustrate how the wobble method tends to favour planets that are either very massive or orbit very close to their stars, or both — selection biases that researchers continue to correct for as instrumentation improves.
11 The Closest Star in Pyxis Is Already Dead
The nearest star within Pyxis's borders is not a glowing nuclear furnace but a cooling ember. Gliese 318 is a white dwarf of spectral class DA5, the burned-out remnant of a once-living star, located approximately 26 to 28.7 ± 0.5 light-years from Earth — the two distance estimates appear in the article, reflecting some measurement uncertainty. It carries about 45 percent of the Sun's mass yet shines with only 0.15 percent of the Sun's luminosity, making it far too faint to see without a telescope: its magnitude is 11.85. White dwarfs like Gliese 318 are the final stage for the vast majority of stars in the Milky Way, including our own Sun roughly five billion years from now. At the opposite extreme of detectability sits WISEPC J083641.12-185947.2, a brown dwarf of spectral type T8p discovered through infrared astronomy in 2011. Located around 72 light-years away, it has a magnitude of 18.79 — thousands of times too faint to see unaided — and was only revealed because modern infrared surveys can detect the feeble heat glow of objects too small to ever ignite as true stars.
12 NGC 2818: A Nebula Inside a Cluster
Among Pyxis's deep-sky showpieces, NGC 2818 stands out for an unusual reason: it is a planetary nebula that appears to lie within a dim open star cluster of magnitude 8.2, a combination that makes for a visually striking and scientifically interesting target. A planetary nebula is the glowing shell of gas expelled by a dying star in its final stages — unrelated to actual planets, the name dates to the 18th century when such objects looked planet-like through early telescopes. Whether the nebula and the cluster are physically associated or merely aligned along the same line of sight is a question the article addresses by noting that NGC 2818A is an open cluster that lies on the line of sight with it, implying the association may be a projection effect. Nearby, K 1-2 is another planetary nebula whose central star is a spectroscopic binary — two stars in close orbit — with jets emanating from the system. The surface temperature of one component has been estimated as high as 85,000 K, hot enough to flood its surroundings with ionising ultraviolet radiation that lights up the surrounding nebula. NGC 2627, an open cluster of magnitude 8.4, is accessible even in binoculars.