Lacerta
“The Lizard” · Northern · best around October 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 little zigzag lizard, squeezed between Cygnus and Andromeda. Its accidental fame: 'BL Lacertae', first catalogued as a variable star, proved to be a blazar — a galaxy's black-hole jet aimed straight at us — and named a whole class of objects.
How to find it
The faint W-zigzag between Cygnus and Cassiopeia.
✦ What lives inside it
- BL Lacertae, the original blazar
The deep dive
Researched for the Atlas from Wikipedia — Lacerta (3,771 characters read) · updated Sep 20, 2026
01 Why Hevelius chose a lizard
When Johannes Hevelius mapped the faint stars between Cygnus, Cassiopeia, and Andromeda in 1687, he needed a creature small enough to fit a cramped patch of sky that ancient cartographers had simply ignored. His first instinct was not a plain lizard but a stellion — a Mediterranean lizard prized for the star-like spots running down its back. He named it "Stellio" before the simpler Latin word Lacerta became the figure's lasting identity. The choice was deliberately modest: Hevelius recognized that no brilliant stars anchored this region, so a small, quick animal suited a small, quiet constellation. That reasoning — matching the creature to the character of the sky patch — was typical of how Hevelius populated gaps in the northern celestial sphere, filling spaces that classical Greco-Roman tradition had left unnamed because nothing there commanded attention.
02 The rivalry of royal dedications
Hevelius was not the only astronomer who eyed this blank stretch of northern sky. Augustin Royer had already proposed filling it in 1670 — seventeen years before Hevelius — by honoring the French king Louis XIV with a constellation called Sceptrum et Manus Iustitiae, meaning the Hand of Justice and Sceptre. Later, Johann Elert Bode tried again in 1787, a full century after Hevelius, proposing Frederici Honores, or Frederick's Glory, as a tribute to Frederick the Great of Prussia. Both royal dedications competed for legitimacy and briefly appeared on European star atlases, yet neither survived into modern usage. When the International Astronomical Union standardized the 88 official constellations, it was Hevelius's humble lizard that prevailed over two flattering political monuments. The episode illustrates how the process of naming the sky was once tangled with court politics and national rivalries, not just astronomical judgment.
03 A star that burns like a tiny, violent sun
One of Lacerta's most scientifically significant residents is EV Lacertae, a red dwarf that spins rapidly and carries a magnetic field powerful enough to generate flares thousands of times more energetic than anything Earth's own sun produces. Despite this ferocity, EV Lacertae normally sits at magnitude 10, far below naked-eye visibility. During a major outburst, however, the flares can briefly lift it to naked-eye brightness — a dramatic swing for a star that otherwise requires binoculars or a small telescope. Flare stars like EV Lacertae are studied intensively because they raise serious questions about habitability: any planet orbiting in a red dwarf's warm zone would be bathed in extreme ultraviolet and particle radiation during such events. EV Lacertae is thus a key reference object for researchers modeling what early Earth-like worlds might endure around the most common type of star in the galaxy.
04 The planet as light as cork Deeper
The binary star system ADS 16402 in Lacerta hosts a planet designated HAT P-1, a gas giant roughly the size of Jupiter. What makes HAT P-1 remarkable is its density: the article's own source describes it as being about the same density as cork, making it one of the puffiest planets known. Standard models of gas-giant interiors struggle to explain how a Jupiter-sized body can be so distended, since at that mass gravity should compress the planet more tightly. The extreme low density implies the planet is inflated beyond what straightforward planetary formation theory predicts, possibly due to intense stellar heating or internal energy sources not yet fully understood. Because ADS 16402 is a binary system, the gravitational environment during the planet's formation was also more complex than single-star cases, adding another variable to an already puzzling object. HAT P-1 is therefore a benchmark target for researchers testing theories of hot-Jupiter inflation.
05 Babcock's Magnetic Star: HD 215441 Deeper
Catalogued at coordinates 22 hours 44.2 minutes right ascension and plus 55 degrees 35 minutes declination, HD 215441 carries the informal title Babcock's Magnetic Star — a name preserved in the Sky Catalogue 2000.0 Volume 2 under its Glossary of Selected Astronomical Names. The designation honors the astronomer who measured its extraordinary magnetic properties, placing it among the chemically peculiar Ap stars known for hosting some of the strongest stellar magnetic fields in the Milky Way. Such fields can be thousands of times stronger than the sun's global field, and they fundamentally alter the distribution of chemical elements across the star's surface, concentrating certain metals into patches that rotate in and out of view. HD 215441 is not a showpiece target for amateur observers — it offers no dramatic visual reward — but it sits in Lacerta as a quiet reminder that even inconspicuous constellations can shelter objects of deep astrophysical importance.
06 BL Lacertae: the object that named a class
In astronomy, it is rare for a single object to lend its name to an entire category of phenomena, yet BL Lacertae accomplished exactly that. For decades it was catalogued as an odd, faintly variable star, but astronomers eventually understood it to be something far larger: the intensely active nucleus of an elliptical galaxy, with a relativistic jet aimed almost directly at Earth. That geometry causes extraordinary brightness variations — BL Lacertae swings irregularly between magnitudes 14 and 17 over the course of just a few days, a range that would be unremarkable for a variable star but is astonishing for a galactic core millions of light-years away. Objects sharing these properties are now called BL Lacertae objects, a subtype of the broader blazar family, which are themselves related to quasars. Detecting it requires a serious amateur telescope, since even at its brightest it sits far below naked-eye reach, but the scientific payoff of monitoring its fluctuations has shaped modern understanding of supermassive black hole jets.
07 Open clusters and a lone planetary nebula
Lacerta's position along the northern edge of the Milky Way populates it with the objects typical of our galaxy's disk: open star clusters rather than the distant galaxies or globular clusters found in less obscured regions. NGC 7243 is the showpiece among these, sitting 2,500 light-years from Earth and resolvable in small amateur telescopes as a few dozen loosely scattered stars, the brightest of which reach magnitude 8. The word "scattered" is intentional — NGC 7243 is not a tight, jewel-box cluster but a relaxed group whose members are spread generously across the eyepiece field. Sharing the constellation is IC 5217, a planetary nebula described as faint, the glowing shell expelled by a dying star. It offers a stark contrast to the cluster: one object born from stellar death rather than stellar youth. Together they illustrate how a single sweep along the Milky Way can reveal very different stages of stellar life in a single constellation.
08 The Great Lacerta Nebula, mostly invisible Deeper
Sh 2-126, known informally as the Great Lacerta Nebula, is described as both massive and faint — a combination that makes it invisible to conventional eyepiece observing but accessible in hydrogen-alpha photography. Hydrogen-alpha light is the deep red emission produced when ionized hydrogen recaptures electrons, and dedicated narrowband filters or cameras tuned to this wavelength can reveal vast clouds that broadband eyes and instruments would miss entirely. The nebula's size earns it the word "Great," yet its low surface brightness means it hides in plain sight against the Milky Way background. For astrophotographers, Sh 2-126 represents a rewarding long-exposure target precisely because the finished image bears almost no resemblance to what any eyepiece shows — the camera transforms an invisible field into a complex, glowing structure. Its existence also underlines why Lacerta, despite appearing nearly empty visually, is actually embedded in active regions of the galactic plane.
09 Chinese serpents and Chumash lizards
The stars of Lacerta were not ignored by every ancient culture — they were simply combined differently. Early Chinese astronomers grouped them, together with stars from the eastern part of Cygnus, into an asterism they called the Flying Serpent. The grouping crosses what Western astronomy now treats as a constellation boundary, revealing how Chinese sky-mapping followed different organizational principles, linking stars by narrative and directional logic rather than by the compact regional boundaries of the Western tradition. On the other side of the world, the Chumash people of California independently recognized this same patch of sky as a lizard and incorporated it into multiple stories — a striking parallel to Hevelius's eventual Latin naming. The Chumash connection was not drawn from European influence; it reflects an independent cultural reading of the same stars. Together, these traditions demonstrate that even a faint, modern-sounding constellation like Lacerta has a richer cross-cultural sky history than its late Western definition might suggest.
10 Alpha and Beta: the constellation's leading stars
Lacerta's brightest star, Alpha Lacertae, is a blue-white main-sequence star of spectral type A1 V shining at magnitude 3.8 from a distance of 102 light-years. It is also an optical double, meaning a second star appears nearby in the sky but the two are not physically associated — just a chance alignment. Beta Lacertae is considerably dimmer at magnitude 4.4, a yellow giant sitting 170 light-years away, and the difference in color between the two is detectable even in binoculars. Together they are the most prominent members of the "W" pattern that gives Lacerta its informal nickname Little Cassiopeia, though this shape is far fainter than the genuine Cassiopeia nearby. Alpha's A1 V classification places it among the hot, white stars that burn through hydrogen more quickly than the sun, while Beta's giant status means it has already left the main sequence — two stars at different points in their lives sharing the same modest constellation.
11 A naval ship carries the lizard's name
Astronomical constellation names have occasionally migrated from the sky into other domains, and Lacerta is no exception. The USS Lacerta, hull designation AKA-29, was an attack cargo ship that served in the United States Navy, named directly after the constellation. Attack cargo ships of the AKA class were workhorses of amphibious operations, designed to transport and land troops along with their equipment and supplies. The naming convention that assigned constellation names to such vessels gave sailors an indirect link to the sky above them, a tradition that connected military service to the long human habit of naming things after the stars. The USS Lacerta represents the practical reach of astronomical nomenclature: a faint lizard sketched into the northern sky by a seventeenth-century Polish-German astronomer eventually christened a warship on the far side of the world, centuries later.