Fornax
“The Furnace” · Southern · best around December 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 chemist's furnace, tucked in a bend of the river Eridanus. Faint itself, it opens onto deep space: the Fornax galaxy cluster and the Hubble Ultra Deep Field — the long-exposure keyhole showing 10,000 galaxies — both live here.
How to find it
Inside Eridanus's southern loop.
✦ What lives inside it
- Fornax galaxy cluster
- The Great Barred Spiral NGC 1365
The deep dive
Researched for the Atlas from Wikipedia — Fornax (12,664 characters read) · updated Sep 20, 2026
01 A chemist's furnace becomes a constellation
When Nicolas Louis de Lacaille sailed to the Cape of Good Hope in the early 1750s, he spent two years cataloguing nearly 10,000 southern stars invisible from Europe. Out of that monumental effort he carved fourteen brand-new constellations from uncharted stretches of southern sky. Almost all of them celebrated the instruments of the Age of Enlightenment — telescopes, compasses, air pumps, and the like. Fornax was his chemical furnace. In his earliest notes he called it le Fourneau Chymique, the Chemical Furnace, and even specified an alembic and a receiver as part of the figure — the glassware of an 18th-century chemist's laboratory. By the time he published his planisphere in 1752, he had trimmed the name to the simpler le Fourneau. On his 1763 chart, he Latinised it to Fornax Chimiae. Later astronomers shortened that to just Fornax, and that is the name the International Astronomical Union has used ever since, assigning it the three-letter abbreviation "For" in 1922.
02 Alpha Fornacis and its blue-straggler companion Deeper
Alpha Fornacis — also known by the proper name Dalim — is the brightest star in the constellation, shining at apparent magnitude 3.91 from a distance of 46.4 ± 0.3 light-years, making it one of the closer stellar systems in Fornax. It is a binary that small amateur telescopes can split. The primary is a yellow-white subgiant 1.21 times the Sun's mass that has used up its core hydrogen and begun to cool and swell, already reaching 1.9 times the Sun's radius. Its companion, at magnitude 6.5, is only 0.78 times the Sun's mass — and it has a peculiar history. Astronomers classify it as a blue straggler, a star that appears younger and bluer than it should given its age. The leading explanation is that it either pulled mass from a now-vanished third body or physically merged with it at some point in the past. The companion is also a surprisingly strong source of X-rays, which is consistent with the turbulent mass-transfer history implied by its blue-straggler status. The system was originally catalogued as 12 Eridani by John Flamsteed before Lacaille claimed it for his new constellation.
03 Three very different giant stars
The three stars that form Fornax's flattened triangle each tell a different story about stellar old age. Beta Fornacis, the shallow southern apex of the triangle, is a yellow giant of spectral type G8IIIb at magnitude 4.5 and 178 ± 2 light-years away. It has ballooned to 11 times the Sun's diameter. Crucially, it is a red clump giant, meaning it has already passed through the violent helium flash and is now quietly fusing helium in its core — a relatively stable phase that gives astronomers a reliable distance-measuring candle. Nu Fornacis, the western point of the triangle, is a very different beast: a blue giant of spectral type B9.5IIIspSi located 370 ± 10 light-years out, packing 3.65 ± 0.18 solar masses and radiating about 245 times the Sun's luminosity through a disk 3.2 ± 0.4 times the solar diameter. It belongs to the class of Alpha2 Canum Venaticorum variables, pulsing in brightness every 1.89 days — exactly its rotation period — because patches of different chemical abundances on its surface rotate into and out of view.
04 Brown dwarfs lurking near the furnace Deeper
Fornax shelters at least two brown dwarfs, objects too small to sustain hydrogen fusion and therefore stranded between planet and star. LP 944-20 is a type M9 brown dwarf about 21 light-years away, carrying roughly 7% of the Sun's mass. Its apparent magnitude of 18.69 puts it far beyond naked-eye or binocular reach. Observations published in 2007 revealed that its atmosphere is rich in lithium and laced with dusty clouds — lithium is normally destroyed by nuclear reactions inside true stars, so its presence confirms that LP 944-20 never achieved stellar ignition. Even more extreme is 2MASS 0243-2453, a T-type brown dwarf of spectral type T6 with a surface temperature of only 1040–1100 K. To put that in perspective, 1070 K is roughly the temperature inside a pottery kiln. This object has just 2.4–4.1% of the Sun's mass and a diameter only 9.2 to 10.6% of the Sun's, and its age is estimated at a wide 0.4–1.7 billion years, reflecting the genuine difficulty of nailing down the properties of such dim, cool objects.
05 Six planetary systems in one small corner of sky
Fornax punches above its weight in exoplanet discoveries, with six confirmed planetary systems tucked inside its modest 398 square degrees. Lambda2 Fornacis hosts a Neptune-mass world found by Doppler spectroscopy in 2009, completing an orbit every 17.24 days around a star about 1.2 times the Sun's mass. HD 20868, an orange dwarf 151 ± 10 light-years away with 78% of the Sun's mass, has a planet roughly twice Jupiter's mass taking 380 days to orbit. WASP-72 hosts a Jupiter-mass world that screams around its host star every 2.2 days. HD 20781 and HD 20782 are a gravitationally bound pair of sun-like stars, each with its own planetary companion — making this a multi-star, multi-planet system. Most recently, HR 858, visible near the naked-eye limit at 31.3 parsecs, was announced in May 2019 to host at least three planets discovered by NASA's Transiting Exoplanet Survey Satellite. That gives Fornax one of the denser concentrations of confirmed exoplanet hosts among the smaller southern constellations.
06 NGC 1316: supernovae that measured the cosmos Deeper
NGC 1316, the optical counterpart of the radio source Fornax A, sits about 62 million light-years away and is one of the closer genuinely active galaxies to Earth. In visible light it appears as a large elliptical galaxy, but dark dust lanes near its core betray a violent recent history: astronomers interpret those lanes as evidence that NGC 1316 recently swallowed a smaller spiral galaxy. Its radio emission comes from extensive lobes on either side, generated by jets from the central supermassive black hole. Those jets are not especially powerful, which causes the lobes to have a diffuse, knotted texture as they push against the surrounding intergalactic medium rather than carving clean channels. What makes NGC 1316 scientifically invaluable is its unusually high rate of Type Ia supernovae. Because Type Ia supernovae serve as standardisable distance candles, the repeated explosions in NGC 1316 have given cosmologists multiple independent measurements, making it a key reference point for calibrating the scale of the universe. An entire cluster of galaxies is associated with this single peculiar object.
07 The Fornax Cluster and its giant heart
The Fornax Cluster lies about 19 megaparsecs, or 62 million light-years, from Earth and spans roughly 6 degrees of sky — covering about 28 square degrees. It is the second richest galaxy cluster within 100 million light-years, surpassed only by the much larger Virgo Cluster. At its centre sits NGC 1399, a giant elliptical galaxy discovered by William Herschel on 22 October 1835, now measured at 130,000 light-years in diameter — slightly larger than our own Milky Way — and located 66 million light-years away. The cluster also contains NGC 1365, a barred spiral and Seyfert galaxy 56 million light-years out, whose central bar is actively driving star formation and feeding a supermassive black hole. NGC 1386 is noted as the only Seyfert galaxy within the cluster itself. The irregularly shaped dwarf NGC 1427A, the cluster's brightest dwarf irregular member, sits in the foreground of NGC 1399 at roughly 52 million light-years. The Fornax Cluster is itself part of a larger structure called the Fornax Wall, and it may be physically associated with the nearby Eridanus Group.
08 Ultracompact dwarfs: a new galaxy class found here Deeper
A remarkable discovery came when a team from the University of Queensland, presenting results at a meeting of the Royal Astronomical Society, described 40 previously unknown dwarf galaxies in Fornax. Follow-up observations using the Hubble Space Telescope and the European Southern Observatory's Very Large Telescope revealed something unexpected: these objects were far smaller than any dwarf galaxy previously catalogued, measuring only about 120 light-years, or 37 parsecs, across. That is extraordinarily compact — for comparison, the Milky Way stretches roughly 100,000 light-years, making these ultracompact dwarfs nearly a thousand times narrower. They constituted an entirely new category of galactic object, now called ultracompact dwarf galaxies. The Fornax constellation can therefore claim a genuine milestone in extragalactic astronomy: it is the place where this class of galaxy was first identified and defined. Whether ultracompact dwarfs are the stripped nuclei of larger galaxies tidally disrupted by the cluster, or represent a fundamentally distinct mode of galaxy formation, remains an active area of research.
09 The Hubble Ultra Deep Field window
One of the most famous images in the history of astronomy points squarely into Fornax. The Hubble Space Telescope's Ultra Deep Field is located within the constellation's boundaries — a tiny patch of sky chosen partly for being extraordinarily dark and empty of nearby bright objects, allowing the telescope to peer as deep into cosmic time as its optics would allow. The image captured thousands of galaxies at enormous distances, many of them among the most distant objects ever resolved by a telescope at the time of its release. Also within Fornax sits UDFj-39546284, a candidate protogalaxy identified in Ultra Deep Field data, though more recent analyses have suggested it may be a lower-redshift source rather than the extremely distant primordial object it was initially thought to be — a reminder that pushing observational limits always comes with genuine uncertainty. The patch of sky that Fornax occupies has therefore contributed disproportionately to humanity's understanding of the early universe.
10 A destroyed galaxy leaves ghostly streams Deeper
Tucked inside Fornax is evidence of cosmic cannibalism on a local scale. The Helmi stream is a small galactic stream found in the constellation — the shredded debris of a small galaxy that the Milky Way tore apart approximately 6 billion years ago. As the Milky Way's gravity overwhelmed this intruder, it stretched and dispersed the victim's stars into a long arc that now winds through the Milky Way's halo, still detectable as a coherent group of stars moving together through space. Separate from this stream, the Fornax Dwarf galaxy — a satellite of the Milky Way in the Local Group — is located about 500,000 light-years away and contains its own globular cluster, NGC 1049. Despite its relatively modest distance compared to galaxies in the Fornax Cluster, the Fornax Dwarf is too faint to be seen in amateur telescopes. It was also linked to a now-questioned candidate extragalactic planet, HIP 13044 b, raising the intriguing possibility — not yet confirmed — that planets might orbit stars in disrupted satellite galaxies.
11 A gamma-ray burst near the brightest light ever seen
In January 2019, astronomers detected GRB 190114C, a gamma-ray burst originating from a galaxy about 4.5 billion light-years away, in the direction of Fornax. Astronomers described it as producing the brightest light ever seen from Earth to that date, calling the event the biggest explosion in the universe since the Big Bang. Gamma-ray bursts are already the most energetic explosions known, typically releasing more energy in seconds than the Sun will emit over its entire lifetime, so a record-breaking example is a scientifically significant event. The proximity to Fornax on the sky is a line-of-sight coincidence rather than a physical association — the burst's source galaxy is vastly more distant than any object in the Fornax Cluster — but it underscores how this one constellation has served as a backdrop for discoveries spanning an enormous range of cosmic scales, from brown dwarfs 21 light-years away to explosions 4.5 billion light-years across the observable universe.
12 Fornax in Chinese sky tradition
Western skywatchers are not the only ones who found meaning in the stars that fall within Fornax's boundaries. In the classical Chinese astronomical system, the stars now assigned to Fornax belonged to the grand celestial division known as the White Tiger of the West, rendered in Chinese as 西方白虎, or Xī Fāng Bái Hǔ. The White Tiger is one of the four cardinal symbols in Chinese astronomy, each governing a quadrant of the sky and associated with a season, a direction, and a set of elemental and mythological meanings. The West and the White Tiger are linked to autumn and to the element metal. This framework is fundamentally different from the Greco-Roman system that produced Lacaille's furnace: rather than tracing individual figures among individual star groups, the Chinese tradition organised vast swaths of sky under guardian symbols. The article does not specify which individual Chinese asterisms within the White Tiger system correspond to specific Fornax stars, but the overarching cultural context places these southern stars in a rich symbolic landscape quite independent of European astronomical history.