Perseus
looking toward
SSW212°
ALT 38° · FOV 94°
🌟ByulGil
observatory
Seoul
37°33′N · 126°58′E
2026.10.22 19:46
LIVE · 25 OF 40 ABOVE
Tonight's Sky
40 CONSTELLATIONS
constellation

Perseus

페르세우스자리
Algol, the Demon Star · The Hero
Autumn · low in the north in May
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Science
The science

The most famous star in Perseus is Algol, known as the "Demon Star." Algol is an eclipsing binary of two stars orbiting each other; every time the dimmer star passes in front of the brighter, its brightness drops sharply and then recovers on a cycle of about 2.9 days. This change, as if the star were winking, can be seen with the naked eye, and the ancients gave it the ominous name "the head of the demon (ghoul)." This constellation is also the radiant of the "Perseid meteor shower," which peaks each August and is counted among the most spectacular meteor displays of the summer nights.

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Mythology
The myth

The hero Perseus was given the task of slaying Medusa, the monster who turned to stone anyone who looked at her. By reflecting her in his mirror-bright shield, he beheaded her without looking directly at her. On his way back he found the princess Andromeda about to be sacrificed to a sea monster, and drawing out Medusa's head, he turned the monster to stone and saved her. In the constellation, Perseus is drawn with a sword in one hand and Medusa's head (Algol) in the other.

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Stars
Main stars (equatorial)
MirfakRA 3.41h · Dec 49.9° · m1.8
AlgolRA 3.14h · Dec 41.0° · m2.1
GammaRA 3.08h · Dec 53.5° · m2.9
DeltaRA 3.72h · Dec 47.8° · m3.0
EpsilonRA 3.96h · Dec 40.0° · m2.9
ZetaRA 3.90h · Dec 31.9° · m2.9
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40 Kuwento ng Konstelasyon

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Byulgil is a stargazing web app that computes the real night sky for your location, anywhere in the world, in real time. Byulgil means "Star Loads", in Korean. Use your current location (GPS) or pick a major city — Seoul, Tokyo, New York, Sydney — to see the sky exactly as it appears there, right now. Star positions come from real J2000.0 equatorial coordinates, converted to horizontal coordinates for your time and place. On mobile, AR mode lets you point your phone at the sky to overlay the constellations in that direction.