Antlia
“The Air Pump” · Southern · best around April evenings
Real star positions and magnitudes (HYG database via D3-Celestial, BSD-3). Lines are the conventional stick figure; north is up.
The story
One of the 14 southern constellations named by Lacaille in the 1750s for scientific instruments — here, the vacuum pump. Faint and quiet, it holds the Antlia Dwarf galaxy and a giant, nearly edge-on spiral, NGC 2997.
How to find it
South of Hydra's long body on southern autumn evenings.
✦ What lives inside it
- NGC 2997 spiral galaxy
The deep dive
Researched for the Atlas from Wikipedia — Antlia (10,570 characters read) · updated Sep 20, 2026
01 A constellation born in a laboratory
When Nicolas-Louis de Lacaille sailed to the Cape of Good Hope for a two-year observing campaign, he catalogued nearly 10,000 southern stars and invented fourteen new constellations to fill the uncharted sky. Almost every one of those constellations honoured a scientific instrument, deliberately celebrating the Age of Enlightenment rather than gods or heroes. Antlia was his tribute to the air pump — specifically, the single-cylinder vacuum pump used by the French physicist Denis Papin in his earliest experiments. Lacaille first described it in French as la Machine Pneumatique in 1751–52, then Latinised the name to Antlia pneumatica on his 1763 chart. Interestingly, the German astronomer Johann Bode depicted a more advanced double-cylinder version of the same pump, showing how even a single constellation could carry different technological meanings depending on who was drawing the map. The scientific community ultimately settled on the simpler machine Lacaille originally had in mind.
02 How a long name became one word
For decades the constellation carried the cumbersome double-word label Antlia pneumatica. In 1844 the English astronomer John Herschel proposed cutting it to a single word, pointing out that Lacaille himself had sometimes abbreviated his own constellation names that way. The suggestion was embraced almost immediately across the astronomical community, and when the International Astronomical Union formally codified the list of 88 modern constellations in 1922, the stripped-down name Antlia was the one enshrined. The official three-letter abbreviation is simply "Ant." The constellation's borders were then geometrically fixed by the Belgian astronomer Eugène Delporte in 1930, defined by a polygon whose east–west right-ascension limits run from 09h 26.5m to 11h 05.6m and whose declination range spans −24.54° to −40.42°. During that same 1930 boundary-drawing exercise, two stars that Lacaille had originally labelled Beta and Gamma Antliae were found to fall inside the neighbouring constellation Hydra, and they were reassigned accordingly — an early reminder that constellation borders are administrative decisions, not physical ones.
03 Stars too faint for ancient sky-watchers
The patch of sky now called Antlia was perfectly visible to ancient Greek observers, yet its stars were simply too dim to inspire a figurative shape or earn a name. The historian Ridpath notes explicitly that the stars of Antlia did not make up any part of the classical depiction of Argo Navis, the great ship of the Argonauts that dominated that region of the southern sky for centuries. Argo Navis itself was an enormous ancient constellation — so enormous that Lacaille split it into hull (Puppis), poop deck, and sails (Vela) in 1763. Antlia sits just north of the stars that form those sails. Chinese astronomers, observing from more northerly latitudes, could see the area and did give its stars meaning: stars in the southern part of Antlia were incorporated into "Dong'ou," representing a region of southern China, while Epsilon, Eta, and Theta Antliae were woven into a celestial temple shared with stars from the neighbouring constellation Pyxis. These are the only named cultural traditions the historical record preserves for this sky region.
04 Alpha Antliae and what aging means for a star Deeper
The brightest star in Antlia, Alpha Antliae, is an orange giant of spectral type K4III located 320 ± 10 light-years from Earth. Its apparent magnitude fluctuates between 4.22 and 4.29, technically making it a suspected variable, though the range is subtle enough that a casual observer would never notice. What makes Alpha scientifically interesting is the story its luminosity tells: it shines with an estimated 480 to 555 times the power of the Sun, a range reflecting genuine uncertainty in the models. Astronomers interpret this energy output as the signature of an ageing star that has exhausted the hydrogen in its core, converting it entirely into carbon, and is now brightening on a trajectory toward becoming a Mira variable — a slow, pulsing red giant that can vary by factors of hundreds in brightness over months. Alpha Antliae offers a snapshot of a stellar middle age almost certainly destined to become a dramatic stellar old age, making it a quiet but instructive object in an otherwise unremarkable constellation.
05 S Antliae: two stars sharing one skin Deeper
S Antliae is one of the more physically extreme objects in the constellation. It is an eclipsing binary of the W Ursae Majoris class, meaning its two stars are so close together that they share a single common envelope of gas and exchange stellar material continuously. The pair dims from magnitude 6.27 to 6.83 in just 15.6 hours as the cooler secondary passes in front of the hotter primary. Modelling the orbital period yields precise masses and sizes: the primary carries 1.94 times the mass of the Sun and 2.026 times its diameter, while the secondary holds 0.76 solar masses and 1.322 solar diameters. Because the two components share an envelope, they have arrived at similar luminosities and spectral types despite their different masses — a levelling effect caused by that intimate physical connection. The system is estimated to be 5 to 6 billion years old. Ultimately, there is no stable long-term future for such a configuration: the two stars will spiral together and merge into a single rapidly spinning star, a fate that no current instrument can watch unfold in real time.
06 HR 4049: a star without a category Deeper
Among the variable stars scattered across Antlia, HR 4049 — also catalogued as AG Antliae — stands apart because astronomers genuinely cannot place it in any known class of variable star. It is an ageing hot star of spectral type B9.5Ib-II, sitting roughly 6,000 light-years from Earth, and it oscillates between magnitudes 5.29 and 5.83 with a period of 429 days. That long, slow cycle does not match the physics of any established variability mechanism. At the same time, the star is undergoing intense mass loss, shedding its outer layers at a high rate. UX Antliae presents a different kind of strangeness: classed as an R Coronae Borealis variable, it sits at a baseline brightness of around magnitude 11.85 but can dim unpredictably to below magnitude 18 — a drop of more than six magnitudes. Its spectrum resembles an F-type yellow-white supergiant, yet it contains almost no hydrogen. Both objects remind observers that stellar physics still has categories waiting to be written.
07 Exoplanets hiding in a faint constellation
Despite its obscurity, Antlia contains two confirmed planetary systems. HD 93083 is an orange dwarf of spectral type K3V — smaller and cooler than our Sun — orbited by a planet roughly as massive as Saturn. That planet was found in 2005 using the radial velocity technique with the HARPS spectrograph, which detects the tiny wobble a planet induces in its star's light. It circles HD 93083 every 143 days at a mean distance of 0.477 AU, placing it in a region somewhat like the inner edge of our own solar system's habitable zone. The second system, WASP-66, centres on a sunlike star of spectral type F4V. Its planet carries 2.3 times the mass of Jupiter and completes a full orbit every 4 days — a so-called hot Jupiter hugging its star at blistering proximity. This planet was identified in 2012 by the transit method, which catches the tiny dip in starlight as a planet crosses the stellar disc. Two very different detection techniques, two very different kinds of worlds, both tucked inside the same inconspicuous constellation.
08 Brown dwarfs at the constellation's edge Deeper
Antlia also harbours objects that blur the line between star and planet. DEN 1048-3956 is a brown dwarf of spectral type M8 lying only about 13 light-years from Earth — close enough in cosmic terms to be a near neighbour, yet at magnitude 17 it is completely invisible without a substantial telescope. Its surface temperature is approximately 2,500 K, cool enough for complex molecules to form in its atmosphere. In 2002, observers detected two powerful flares from this object, each lasting 4 to 5 minutes — a surprising burst of activity for a body that never ignited sustained fusion. Even more extreme is 2MASS 0939-2448, a gravitationally bound pair of brown dwarfs so cold that their estimated effective temperatures are only around 500 and 700 K — or possibly both near 600 K, with masses near 30 Jupiter masses each, though a second solution puts them at about 25 and 40 Jupiter masses. That uncertainty reflects how poorly understood the very coldest brown dwarfs remain; distinguishing a massive planet from a failed star at these temperatures is an open problem in astrophysics.
09 The Antlia Cluster: third closest to home
Antlia lends its name to one of the nearest large galaxy clusters in the universe. The Antlia Cluster, catalogued as Abell S0636, belongs to the sprawling Hydra–Centaurus Supercluster and sits at a distance of 40.5 to 40.9 megaparsecs from Earth — equivalent to roughly 132 to 133 million light-years. Only the Virgo Cluster and the Fornax Cluster are closer to our Local Group of galaxies, making the Antlia Cluster the third nearest such structure. Two giant elliptical galaxies anchor the cluster: NGC 3268 leads the southern subgroup while NGC 3258 leads the northern one. Together with roughly 234 galaxies in total, the cluster lies in the southeastern corner of the constellation. It is worth noting that the cluster sits in the sky direction of Antlia but has no physical relationship to the constellation's stars, which are measured in hundreds of light-years rather than hundreds of millions.
10 NGC 2997 and the Local Group's quiet neighbour
The brightest galaxy visible within Antlia's boundaries is NGC 2997, a loosely wound face-on spiral of Hubble type Sc shining at magnitude 10.6. To most amateur telescopes it appears unremarkable — a soft, diffuse glow — but long-exposure photographs reveal bright clusters of young stars punctuated by intricate dark dust lanes threading through the spiral arms. In pointed contrast, the Antlia Dwarf is a tiny spheroidal galaxy at magnitude 14.8, discovered in 1997 and confirmed as a member of the Local Group, the same family of galaxies that contains the Milky Way and the Andromeda Galaxy. A third galaxy, announced in 2018, is Antlia 2 — an extremely low surface brightness object found near Epsilon Antliae. Antlia 2 is a satellite galaxy of the Milky Way itself, meaning it orbits our own galaxy. Its discovery illustrates how modern surveys continue to uncover significant structures hiding in plain sight, invisible to earlier instruments simply because they spread their light too thinly across the sky.
11 A supernova remnant of extraordinary scale
One of the most physically imposing objects associated with Antlia is the Antlia Supernova Remnant, described as one of the largest supernova remnants in the sky. A supernova remnant is the expanding shell of gas and magnetic field left behind when a massive star destroys itself in a catastrophic explosion. The sheer angular size of the Antlia Supernova Remnant on the sky indicates that it is either physically enormous, relatively close to Earth, or both — though the article does not pin down an exact distance. Such remnants are scientifically valuable because they accelerate cosmic ray particles to near-light speed, enrich the interstellar medium with heavy elements forged in the dying star, and trigger the compression of nearby gas clouds that can initiate new star formation. Its existence in this faint, seemingly uneventful constellation is a reminder that dramatic stellar death can leave marks across a significant fraction of the visible sky long after the original explosion has faded.
12 The size and shape of an overlooked corner
Antlia covers 238.9 square degrees of sky, which amounts to 0.579 percent of the entire celestial sphere, ranking it 62nd in area among the 88 modern constellations — solidly middle of the pack in size, yet visually one of the most anonymous. For reference, 238.9 square degrees is roughly 1,200 times the area of the full Moon. The constellation is completely visible to anyone south of 49 degrees north latitude, which includes virtually all of the populated Southern Hemisphere and most of Europe and North America down to about the level of Paris or Vancouver. Its celestial neighbours define its position neatly: the serpentine constellation Hydra stretches along its entire northern border, while Pyxis touches it to the west, Vela to the south, and Centaurus to the east. Within these borders, 42 stars reach apparent magnitude 6.5 or brighter — the rough limit of naked-eye visibility under excellent dark skies — though none approaches the kind of brightness that makes a constellation easy to spot or trace.