Perseus Constellation

By Alexander Merz · Updated on 30 September 2026 · Details checked on 24 October 2026

The constellation Perseus is a constellation of the northern sky in the middle of the Milky Way, between Cassiopeia and Auriga. Its brightest star is Mirfak (magnitude 1.8), its most famous is Algol, the “Demon Star”, which fades noticeably for a few hours every 2 days and 21 hours.

More in our overview: Constellations.

Perseus at a glance: the key facts

Finding Perseus: from the “W” of Cassiopeia to Capella

The easiest way to find Perseus uses two bright signposts: the “W” of Cassiopeia and the yellowish star Capella in Auriga. Perseus lies right between them, a curving chain of stars hanging down from the Milky Way.

• Step 1: Look north-east for the “W” of Cassiopeia. On autumn evenings it stands high, in winter almost overhead.
• Step 2: Follow the Milky Way from the “W” down to the left towards Capella, the brightest star in this part of the sky (mag 0.1).
• Step 3: About halfway you reach Mirfak, a bright star inside an eye-catching little group. From there a chain of stars turns down towards Algol.

The distances help you judge the scale: Mirfak and Algol are about 9° apart, roughly a hand’s width at arm’s length. From Mirfak to Capella it is 19°, from the star Segin in the “W” to Mirfak 18°.

Algol – the “Demon Star” in Perseus

Algol (β Persei) is the best-known variable star in the whole sky and the reason many people have heard of Perseus at all. Normally it shines at magnitude 2.1, almost as bright as Polaris.

Every 2 days, 20 hours and 49 minutes, however, it drops to magnitude 3.4 – more than three times fainter. The whole event lasts about ten hours: roughly five hours down and five back up.

Why Algol changes its brightness

Algol is not a single star but a close star system. A bright, bluish main star is orbited in just under three days by a larger but much fainter orange companion.

When this companion passes in front of the main star as seen from Earth, it blocks a large part of its light. Astronomers call such a system an eclipsing binary, and Algol gave its name to a whole class, the Algol variables.

The young Englishman John Goodricke suggested this eclipse explanation in 1783 and also measured the period. Today we know that a third star orbits the pair, once every 1.9 years or so.

Following an Algol minimum with the naked eye

For Algol you need no instrument, only comparison stars. You estimate its brightness by comparing it with stars whose brightness does not change.

Here is how: start two to three hours before the predicted minimum and compare Algol with the stars in the table every 20 to 30 minutes. Each time, note the time and whether it looks brighter, equal or fainter than the comparison star.

Next Algol minima until March 2028

We calculated the times below ourselves for the centre of Germany (Central European time) and only included minima between 7 pm and 3 am with Algol at least 25° high. They are based on two published Algol ephemerides (Sky & Telescope 2004 and the Insula Astra calculator), and we give their mean. From April 2027 we extended the series with a period of 2.867328 days, tied to the times up to March, and also required the Sun to be at least 6° below the horizon – otherwise summer minima would fall in bright twilight.

Allow for about ± 30 minutes of uncertainty: the two ephemerides differ by 34 minutes because Algol’s period changes slightly. Since the minimum stretches over hours, this does not matter for the eye; for times to the minute, the Sky & Telescope calculator is the reference.

Double star in Perseus: crossword answers

The crossword clue “double star in Perseus” with five letters almost always has one answer: ALGOL. It is a double star in the literal sense, because two stars orbit and eclipse each other.

Miram is η Persei, Misam κ Persei, Atik ο Persei and Menkib ξ Persei. If ALGOL does not fit the grid, check these four.

Mirfak and the Alpha Persei Cluster

At magnitude 1.8, Mirfak (α Persei) is the brightest star in Perseus, a yellowish-white supergiant about 590 light years away. The name comes from Arabic and means “elbow”.

Around Mirfak lies a swarm of bright stars, the Alpha Persei Cluster (Melotte 20). It is about 3° across, six full-moon widths, and consists of young, bluish stars moving through space together.

The Double Cluster h and χ Persei

Between Perseus and Cassiopeia lies the finest binocular target of the autumn sky: two open star clusters side by side, h Persei (NGC 869) and χ Persei (NGC 884). Their centres are just under half a degree apart.

Under a dark sky you can see both with the naked eye as a hazy patch in the Milky Way, about 7° from the star Segin in the “W”. The clusters are about 7,500 light years away and, at around 14 million years, very young.

Binoculars or telescope for the Double Cluster?

Binoculars win here: both clusters fit into the field together, including the chain of stars that links them. Even 10×50 binoculars show dozens of individual stars, including a few reddish giants.

The right choice for h and χ Persei: Nikon Action 10x50 CF Binoculars

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A telescope at low magnification shows each cluster on its own with hundreds of stars. You only get both at once with a wide-field eyepiece, at around 20 to 30 times magnification.

When a telescope pays off in Perseus

Binoculars are not enough for three targets in Perseus: the double stars ε, ζ and η Persei and the Little Dumbbell Nebula M 76. A 60 mm telescope already splits Epsilon Persei, and η Persei shows a lovely orange-and-blue colour contrast.

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M 34 and other deep-sky objects in Perseus

Besides the Double Cluster, Perseus has a handful of rewarding targets. The Milky Way runs right through it but looks fainter here than in summer, because dark clouds swallow a lot of light.

M 34 lies a good 5° west of Algol, on the way to Andromeda. In binoculars it appears as a small, loose swarm of about a dozen stars; in a telescope at low power you will count many more.

The California Nebula shows up almost only in photos, because its light is spread over a large area. And the Perseus galaxy cluster, some 240 million light years behind the stars of the constellation, is a job for large telescopes and astrophotography.

Perseids: the radiant in the constellation Perseus

Every August the Perseids, the best-known meteor shower of the year, seem to come out of Perseus. Their radiant, the apparent starting point of the trails, lies about 7° from the Double Cluster.

The peak falls on 12/13 August. When and how to watch is explained on our Perseids page, and all other showers are in the meteor shower calendar.

Visibility month by month

Perseus lies so far north that from Germany it never sets completely. Even on summer evenings Mirfak stays about 11° above the northern horizon, and Algol grazes it at 2°.

The table shows altitude and direction at 10 pm local time (CET or CEST) for the centre of Germany, for the middle of each month, calculated by us. The highlighted months are the best.

In December, Mirfak is almost overhead at 10 pm, up to 88° high. Between Hamburg and Munich the altitudes differ by at most about 3°, which hardly changes the overall picture.

The brightest stars in Perseus

What stands out is the wide range of distances: the stars of the figure lie between 90 and more than 1,000 light years away. Only as seen from Earth do they form a connected shape.

Mythology: Perseus, Medusa and Andromeda

In Greek legend, Perseus is the son of Zeus and Danaë. His most famous adventure: he cut off the head of the Gorgon Medusa, whose gaze turned everyone to stone, looking at her only in the reflection of his shield.

On his way back he rescued Andromeda, who had been chained to a rock as a sacrifice to a sea monster. Andromeda, her parents Cepheus and Cassiopeia, the monster (Cetus) and the winged horse Pegasus all stand nearby in the sky today.

In the figure, Algol represents the head of Medusa that Perseus holds in his hand. The name comes from the Arabic “ra’s al-ghūl”, head of the demon, which later gave rise to the nickname “Demon Star”.

Perseus is one of the 48 classical constellations described by Ptolemy in the 2nd century. It is not a zodiac constellation; the Sun never passes through it.

Frequently asked questions about the constellation Perseus

Which star in the constellation Perseus has 5 letters?

The answer is almost always ALGOL, the famous eclipsing binary. Rarer five-letter answers are MIRAM (η Persei) and MISAM (κ Persei).

What is the brightest star in Perseus?

The brightest star is Mirfak (α Persei) at magnitude 1.8, also spelled Marfak. Algol is the second brightest only outside its minima.

What does the constellation Perseus represent?

It shows the Greek hero Perseus, who defeated Medusa and rescued Andromeda. Algol marks the severed head of Medusa in his hand.

Is Perseus a sign of the zodiac?

No, Perseus is not part of the zodiac. The Sun never passes through this constellation on its yearly path.

Can you see Perseus all year round?

From Central Europe yes, because Mirfak is circumpolar and never sets. In early summer, though, the constellation is so low in the north in the evening that it hardly stands out in the haze.

When is the next minimum of Algol?

The evening minima until March 2028 are listed in our table above. Algol fades every 2 days and 21 hours, so each minimum comes about three hours earlier on the clock than the one before.

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