Perseus
The hero between Cassiopeia and the Pleiades
Best on December–February evenings · northern sky.
Perseus is a rich northern constellation sitting right in one of the Milky Way's brightest stretches, sandwiched between the W of Cassiopeia and the sparkle of the Pleiades. It's best known for its brilliant lead star Mirfak and for Algol, the famous 'Demon Star' that fades and brightens over a few days — one of the sky's most accessible variable stars.
How to find it
On winter evenings, look for the unmistakable W of Cassiopeia high in the north, then sweep your eye southward toward the Pleiades cluster. Perseus fills that gap between them, a loose chain of stars curving through the Milky Way. Mirfak, the brightest of the bunch, sits near the middle of that chain and is easy to pick out.
Brightest stars
Mirfak (α Per) leads at magnitude 1.79, a warm yellow-white supergiant at the heart of the constellation. Algol (β Per) follows at magnitude 2.12 — but watch it over several nights, because it dims noticeably as its dimmer companion passes in front of it.
Worth seeing
Algol is the real showpiece: nicknamed the Demon Star, it's one of the easiest variable stars to follow with the naked eye, dropping from magnitude 2.12 to noticeably fainter and back again over a rhythm of less than three days.
Frequently asked
When is Perseus visible?
Perseus is best seen on winter evenings, December through February, when it rides high in the northern sky for northern hemisphere observers.
What are the brightest stars in Perseus?
Mirfak (magnitude 1.79) is the brightest, followed by the famous variable Algol (2.12), then Gorgonea Tertia (3.39), Miram (3.76), Misam (3.8), and Atik (3.83).
Which hemisphere is Perseus best seen from?
Perseus is a northern-sky constellation, best seen from the northern hemisphere, where it climbs high on winter nights between Cassiopeia and the Pleiades.
Nearby constellations
Aries · Auriga · Cassiopeia · Andromeda · Taurus · Cepheus · Orion · Pisces