Related

Start at Cassiopeia's W (or M). The star at its eastern end points roughly toward Mirfak, Perseus's brightest star and an easy naked-eye target even from a modestly light-polluted yard. From Mirfak the chain bends south through Algol and back up toward Gamma and Eta, near the Cassiopeia border. Perseus is a constellation of autumn and winter evenings; look for it climbing the northeastern sky after dark from September on, and standing high overhead by midwinter.

RA is in decimal hours, Dec in decimal degrees, both J2000 — the same figures the site's own chart is drawn from. Magnitudes are visual.

Delta and Epsilon Persei are two of just four stars in the sky to carry Sámi names, adopted by the IAU's Working Group on Star Names in December 2025 alongside 49 Cassiopeiae (Rangifer) and 2 Ursae Minoris (Tarandus) — together they form a reindeer bull and cow, a small tribute to Sámi sky-culture set among four otherwise-unrelated constellations.

Algol is an eclipsing binary: a dim companion star passes in front of the brighter primary every 2.867 days, and for about ten hours of each cycle the combined light drops from magnitude 2.1 to 3.4 — roughly a two-thirds dimming, visible without any instrument if you know when to look. Italian astronomer Geminiano Montanari recorded the dimming in 1667; the English amateur John Goodricke, in 1782–83, timed it accurately enough to propose that an unseen companion star was eclipsing the bright one — a correct hypothesis that took until 1889, when Hermann Vogel measured its spectrum shifting back and forth, to be confirmed.

Whether anyone noticed the variability before Montanari is genuinely contested, not settled. The Arabic name — Ra's al-Ghūl, "the demon's head" — is often cited as proof that ancient skywatchers already knew something was strange about the star. That argument is weaker than it looks: Ptolemy, in the Almagest around 150 CE, simply calls it "the bright one in the Gorgon's head," a positional description tied to the Greek myth of Medusa, and the Arabic name itself dates from centuries after Ptolemy. A star marking a monster's severed head does not need to blink to earn a sinister name. The stronger case for ancient awareness comes from a different direction: a team led by Sebastian Porceddu and Lauri Jetsu at the University of Helsinki argued, from 2012 onward, that the Egyptian Cairo Calendar papyrus (dated roughly 1244–1163 BCE) encodes a 2.85-day period in its record of "raging" and "peaceful" days tied to the god Horus — startlingly close to Algol's real 2.867-day period, with the small gap plausibly explained by orbital changes over three millennia. Other astronomers have found the statistics suggestive but not conclusive, and the claim remains actively debated rather than accepted fact.

The Perseids are debris shed by comet 109P/Swift-Tuttle, a large periodic comet on a roughly 133-year orbit that last passed through the inner solar system in 1992 and is not due back until around 2126; Earth crosses the trail it has left behind every year regardless. The shower is active from mid-July to late August and peaks around 11–13 August, with a radiant — the point the meteors appear to stream from — sitting near Algol, at roughly RA 3h12m, Dec +58°. Under a dark sky with no Moon, rates can top 100 meteors an hour at the peak; the shower has been tracked in Chinese records for roughly two thousand years, making it one of the longest continuously observed astronomical events.

The story, in outline: Perseus's mother Danaë was locked away by her father Acrisius after an oracle warned her son would kill him; Zeus reached her anyway, and Perseus grew up to be sent — by the scheming king Polydectes — to fetch the head of Medusa, the one mortal Gorgon, whose gaze turned onlookers to stone. With help from Hermes and Athena, and directions extracted from the Graeae, Perseus beheaded Medusa while looking only at her reflection in a polished shield, then flew home on winged sandals with the head sealed in a bag. Hesiod's Theogony (c. 700 BCE) already has the winged horse Pegasus and the warrior Chrysaor springing from Medusa's neck at the moment of the beheading — the earliest surviving version of that detail. On the way home Perseus spotted Andromeda chained to a sea cliff, killed the monster sent to devour her, and married her. Fragments of the story appear as early as the 5th-century-BCE Athenian writer Pherecydes; the fullest surviving accounts are Roman — Ovid's Metamorphoses and the mythographic Bibliotheca attributed to Apollodorus. The constellation itself is catalogued in Eratosthenes' Catasterismi (3rd century BCE) and Hyginus's Poetica Astronomica, and Ptolemy lists it among the Almagest's 48.

Arabic sky-lore treated this region on its own terms rather than as a translation of the Greek scene: Bedouin astronomers had independent names for individual bright stars here, without necessarily reading the whole figure as Perseus and Medusa. Later Islamic manuscript art went further — surviving depictions sometimes redraw Medusa's severed head as a bearded man's face, apparently because artists working from earlier European images of the Gorgon's snake-wreathed head (a gorgoneion) mistook the writhing serpent-hair for a beard. No Babylonian equivalent to Perseus is confidently identified in the MUL.APIN tradition; this is one figure where the trail simply does not reach back that far.

• Andromeda — the princess Perseus rescues and marries.
• Cepheus — Andromeda's father, king of the kingdom Perseus saves.
• Pegasus — born from Medusa's blood at the moment of her death.