Sextans
“The Sextant” · Both (straddles the celestial equator) · 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
Hevelius's measuring sextant — placed, he joked, between the Lion and the Water Snake because his own instruments had survived a fire between 'fiery' star signs. Extremely faint.
How to find it
The blank area south of Regulus.
✦ What lives inside it
- The Spindle Galaxy
The deep dive
Researched for the Atlas from Wikipedia — Sextans (4,973 characters read) · updated Sep 20, 2026
01 A constellation born from disaster
Johannes Hevelius did not invent Sextans to fill a gap in the sky — he created it as a monument to grief. On 26 September 1679, fire destroyed his Danzig observatory, taking with it a prized astronomical sextant he had relied on for years of careful positional measurement. He described the catastrophe in the preface to his Annus climactericus, published in 1685, and when he finally catalogued the constellation two years later in 1687, he named it Sextans Uraniae — the sextant of Urania, muse of astronomy. The tribute was bittersweet: the constellation honors an instrument that no longer existed. Remarkably, Hevelius had already rebuilt enough equipment by December 1680 to observe the great comet of that year, demonstrating a resilience that matches the quiet persistence required to study such a faint patch of sky.
02 Why its stars went unlabeled for so long
John Flamsteed catalogued 41 stars within Sextans and numbered them, but the constellation's stars were so faint that the next logical step — assigning Bayer Greek-letter designations — was skipped entirely for a long time. Francis Baily, who prepared an important star catalogue in the nineteenth century, looked at the roster and decided that because none of the stars reached magnitude 4.5, the traditional threshold for such labels, he would leave them unlettered. It fell to the American astronomer Benjamin Apthorp Gould to finally letter the five brightest stars Alpha through Epsilon, which he published in his Uranometria Argentina. The episode is a small but telling reminder that constellation boundaries and star designations evolved through a patchwork of individual decisions by different astronomers across different centuries, not from a single coordinated plan. In total, 38 stars within Sextans are brighter than or equal to apparent magnitude 6.5.
03 Alpha Sextantis: the lone star above fifth magnitude Deeper
Alpha Sextantis holds a slim but real distinction: it is the only star in the entire constellation that clears fifth magnitude, shining at an apparent magnitude of 4.49. Its spectral class is A0 III, placing it among the aging giant branch of A-type stars — a class ordinarily associated with the crisp, hydrogen-burning main sequence, but here edging away from it. At 280 ± 20 light-years from the Solar System, Alpha Sextantis is close enough for modest telescopes to resolve its disk characteristics. Its age, estimated at 385 million years, is the key figure: the star is now exhausting the hydrogen fuel at its core and beginning the slow expansion that will carry it off the main sequence entirely. For context, 385 million years ago on Earth, the Devonian period was underway and the first forests were just appearing. The star's quiet evolutionary drama unfolds across timescales that dwarf human civilization.
04 Gamma Sextantis: two stars almost impossible to split Deeper
The second-brightest star in the constellation, gamma Sextantis, carries an apparent magnitude of 5.05 and is a binary system consisting of two A-type main-sequence stars classified as A1 V and A4 V. The pair are separated by just four-tenths of an arcsecond — an angular gap so tiny that resolving them requires a telescope with an aperture of at least 30 centimeters. Despite that physical closeness in the sky, their orbital period stretches to 77.55 years, and the orbit is eccentric rather than circular. The system sits 280 ± 10 light-years from the Solar System, almost exactly the same distance as Alpha Sextantis, though the two stars are unrelated. Gamma Sextantis is a textbook example of how a binary system can look like a single star for most observers, revealing its true nature only under the most demanding optical conditions.
05 Beta Sextantis and the art of standard stars Deeper
Beta Sextantis, at magnitude 5.07, is marginally fainter than its gamma counterpart and sits at 364 ± 10 light-years distance. Its spectral class, B6 V, marks it as a hot blue-white star on the main sequence. What makes Beta Sextantis scientifically significant beyond its appearance is its role as a standard star in the MK spectral classification system — the framework astronomers use to categorize stellar spectra and anchor comparisons across the entire sky. Standard stars must be stable, well-characterized, and representative, which is why it is notable that Beta Sextantis is also suspected to be an Alpha2 Canum Venaticorum variable, showing periodic brightness changes with a period of 15.4 days. If confirmed, that variability would complicate its use as a photometric standard, illustrating how even the benchmark stars against which others are measured can turn out to be more complex than they first appear.
06 A triple star system measured in millennia Deeper
Among the constellation's multiple-star systems, 35 Sextantis stands out for its sheer orbital timescales. The outer pair of this triple system consists of two evolved K-type giants of equal mass, each about twice the mass of the Sun, separated by 6.8 arcseconds. They take roughly 23,000 years to complete one orbit around each other — a period so long it exceeds the entire span of recorded human history by a factor of more than two. Meanwhile, the secondary star is itself a spectroscopic binary: a single-lined system in which a companion of 0.58 solar masses orbits its host in 1,528 days, following a relatively eccentric path. The whole system lies approximately 700 light-years away. 35 Sextantis is a quiet reminder that gravitational hierarchies in stellar systems can operate across wildly different timescales simultaneously, from years to geological epochs.
07 NGC 3115 and a slice through a lenticular galaxy
The most celebrated deep-sky object in Sextans is NGC 3115, a lenticular galaxy presented to observers nearly edge-on. A lenticular galaxy occupies an intermediate category between ellipticals and spirals — it has a disk structure but lacks the prominent spiral arms that define galaxies like the Milky Way. The edge-on orientation makes NGC 3115 appear as a luminous spindle, its central bulge swelling visibly above the thin plane of the disk. The article identifies it as the only noteworthy deep-sky object in the constellation, a frank assessment of a region that is largely transparent to nearby structure. That transparency is, paradoxically, what makes Sextans scientifically valuable for deep survey work — the relative absence of nearby bright stars and nebulae means that very faint and very distant objects are easier to study here than in more crowded parts of the sky.
08 The COSMOS window into the early universe
The field studied by the COSMOS project — a major deep survey carried out with the Hubble Space Telescope — falls within the boundaries of Sextans, and it has produced several landmark findings. In 2016, the most distant known galaxy cluster, CL J1001+0220, was identified here at a redshift of z = 2.506, placing it 11.1 billion light-years from Earth. At that distance, the light now reaching our telescopes left the cluster when the universe was less than three billion years old. Separately, the dwarf irregular galaxy Sextans B, a member of our own Local Group, shines at magnitude 6.6 from a distance of 4.3 million light-years — a reminder that the same patch of sky can simultaneously contain objects at wildly different depths, from galactic neighbors to structures near the observable edge of the cosmos.
09 Cosmos Redshift 7 and the first generation of stars Deeper
In June 2015, astronomers announced evidence for Population III stars embedded within the galaxy known as Cosmos Redshift 7, found in Sextans at a redshift of z = 6.60. Population III stars represent the theoretical first generation of stellar objects to form after the Big Bang — composed almost entirely of hydrogen and helium, with essentially no heavier elements inherited from earlier generations. Their significance is profound: it is believed that Population III stars initiated the production of chemical elements heavier than hydrogen, seeding the universe with the raw materials needed for later rocky planets and, eventually, life as we know it. The Cosmos Redshift 7 detection was described as evidence rather than a confirmed detection, which reflects the genuine difficulty of identifying such ancient and extreme objects and the ongoing nature of that research frontier.
10 Sextans on the celestial equator
Sextans sits directly astride the celestial equator, with its official boundaries spanning right ascensions between 09h 41m and 10h 51m and declinations between +6.43° and −11.7°. Those coordinates mean the constellation straddles the equatorial plane, making it theoretically visible from virtually every inhabited location on Earth at some point in the year. Its borders, formalized by Belgian astronomer Eugène Delporte in 1930 in his standardizing work for the International Astronomical Union, are defined by a notably square outline. Because Sextans also sits close to the ecliptic plane, the Moon and planets regularly pass through it, particularly through its northeastern corner. The IAU formally adopted the three-letter abbreviation Sex in 1922, a fact that the constellation's name makes unavoidable and that astronomers note with characteristic understatement.
11 Neighboring constellations and how they frame it
Sextans occupies a quiet triangle of sky bounded by three neighbors of very different character. To the north lies Leo, one of the most recognizable zodiacal constellations, dominated by the bright star Regulus and the distinctive sickle asterism. To the southwest, the vast, winding body of Hydra — the longest constellation on the entire sky — provides a dramatic backdrop. To the southeast, Crater the Cup completes the frame. None of these neighbors lend their brightness to Sextans itself; the constellation sits in what amounts to a luminous gap between more prominent figures. This positioning is part of why Hevelius was able to carve out space for it at all: the region genuinely needed a name, and the faint stars there had not been claimed by older traditions. It is a medium-sized constellation by modern standards, though its visual faintness makes it feel far smaller.