Star Constellations: Perseus 'the Hero'
Created | Updated Jan 17, 2008
Perseus seek for by her feet
Whichever at his shoulder are revolving.
Tallest of all his compeers at the North he towers.
His right hand stretches toward the chair of his bride's mother1.
- Phenomena of Aratos by Nathaniel Langdon Frothingham (1793 - 1870).
| Latin: | Perseus |
| Genitive: | persei |
| Short form: | Per |
| Area: | 615 sq deg |
| Co-ordinates: | 3h, +45° |
| Zodiac: | no |
| Origin: | ancient |
Perseus is a typical constellation of the autumn and winter sky. However from European latitudes (or more northern) the constellation is at least partly circumpolar. It is very easy to find, since it is surrounded by very well-recognised constellations such as the 'W' of Cassiopeia, Auriga, Andromeda and Taurus. The 'Perseus Arm' is one of four major spiral arms of our galaxy, the Milky Way. We are in the minor 'Orion Arm'.
The constellation is 28 degrees in length, one of the largest in the heavens. Its principal stars form a curved line that bears the name 'the Segment of Perseus' - a figure that is almost as much of a stellar landmark as the Great Square of Pegasus, in mythology the winged horse. Perseus is directly above the Pleiades (M45), the unmistakable naked-eye star cluster in the constellation Taurus, and rises just before Andromeda.
Mythology
Perseus was a hero in Greek mythology. Unfortunately his story has been told in various versions. All sources agree that he was the son of Zeus and the mortal Danaë. Perseus and his mother had to flee to an island where King Polydectes ruled. The King married Danaë and after Perseus had grown up, he was sent out in the world for adventure; he was supposed to cut off the head of the terrible monster Medusa. Other sources claim that Polydectes wanted to have Danaë's love, but she rejected his approaches. Perseus had to go and kill Medusa to save his mother from the intrusive king.
Medusa used to be a beautiful servant of Pallas Athena, the Greek goddess of Wisdom. But in hubris she compared herself with Athena, and so Athena turned her into a Gorgon, a terrible creature with snakes instead of hair, and boar's teeth. She was so frightening that anybody who looked at her face turned into stone. Another source says that Poseidon, the Greek god of the sea, raped Medusa, and Athena bewitched her because of the lost virginity. (Surely
this is a questionable punishment, however it was typical of Athena: Arachne - who had also regarded herself to be better looking than the goddess, continued life as a spider.)
In any case Perseus was a favourite of Athena and Hermes the messenger of the gods, so he got valuable items from them: a magic hood for attaining invisibility, winged sandals so that he could fly, a sickle, a very well polished shield, and a bag. With this equipment he approached Medusa while she and her Gorgon
sisters2 were sleeping. He watched them indirectly via the shield which acted as a mirror, to avoid being turned into a rock. He cut off Medusa's head with the sickle and put it in the bag. Perseus sometimes used this head as a powerful weapon by just showing it to the enemy.
His second heroic deed was the rescue of Andromeda, daughter of King Cepheus and Queen Cassiopeia, from the sea monster Cetus. Perseus married Andromeda and became the ancestor of a whole race of people. All of the main figures of this legend have been set in the sky as constellations by the gods. Even Medusa found its place: the star Algol represents her eye.
Principal Stars
The scientific star names are simple to understand (if you know your Greek alphabet). The brightest star in the constellation is alpha, the next brightest is beta, and so on. Some are named stars, like alpha Ori is known as Betelgeuse; others are known by their catalogue numbers or 'designation'.
The brightest star in Perseus is Mirphak (alpha Persei), a white supergiant. Algol is a particularly interesting star. It belongs to a class of variables that bears Algol's name. Stars of that kind actually consist of two stars that are in orbit around each other with a rather high frequency. So, within days, the smaller component is visible next to, or in front of, the bigger companion, or hidden behind it. Consequently we see a change in brightness.
As already mentioned, Algol represented the terrible eye of Medusa for the ancient Greeks; in ancient Arabia it was a devilish demon called Gul. For the Hebrew people Algol was Lilith, Adam's first wife, who had turned into a vampire.
Star Table
| Star | Designation | Name | Brightness (m) | Distance (light years) | Remarks |
| α Per | alpha Persei | Mirfak (elbow) | 1.8 | 592 | Yellow supergiant |
| β Per | beta Persei | Algol (the Ghoul3) | 2.1–3.4 | 95 | Eclipsing binary |
| γ Per | gamma Persei | Al Fakhir (the Excellent One) | 2.9 | 256 | Multiple star system |
| δ Per | delta Persei | Adid Borealis | 2.9 | 527 | Blue giant |
| ε Per | epsilon Persei | Adid Australis | 3.0 | 538 | Multiple star system |
| ζ Per | zeta Persei | Menkhib | 2.9 | 980 | Blue supergiant (19 x solar mass) |
| η Per | eta Persei | Miram | 3.76 | 1,330 | Orange supergiant |
| θ Per | theta Persei | 13 Persei | 3.9 | 36 | Yellow dwarf |
| ι Per | iota Persei | SAO 38597 | 4.05 | 34 | Yellow dwarf |
| κ Per | kappa Persei | Misam | 3.8 | 112 | Orange giant: Triple star system |
| ξ Per | xi Persei | Menchib | 4.0 | 1,600 | Blue giant illuminates NGC 1499 |
| ο Per | omicron Persei | Al Atik | 3.8 | 1,480 | Binary star system |
| HD 16175 | HIP 12191 | unnamed | 7.3 | 195 | Yellow G-type. Has a planet HD 16175 b (discovered Sept 2007) |
| HD 17092 | SAO 38313 | unnamed | 7.7 | 355 | Orange giant. Has a planet HD 17092 b (discovered 2007) |
| HD 23596 | SAO 39110 | unnamed | 7.25 | 170 | Yellow main sequence. Has a planet HD 23596 b (discovered 2002) |
| GK Per | Nova Persei 1901 | GK Persei | 0.2 max | Nova remnant discovered 1901. Brightest modern-time nova until 1918. |
Extrasolar Planets
There are three stars with planets - that we know of - in Perseus. HD 23596 b is at least eight times as massive as Jupiter, our Solar System's largest planet. HD 17092 b has an eccentric orbit and is 1.3 AU4 from its parent star, that is around a third further out than Earth's distance from our Sun. HD 16175 b is 4.5 times the mass of Jupiter, which is the usual marker extrasolar planets are given, now known as the 'Jovian scale'.
The Holy Grail of astronomers is to find the right size (rocky) planet orbiting its parent star at the correct distance for life to be viable and sustainable. The orbit would need to be non-eccentric, and the parent star should be stable. This 'just right' set of circumstances has earned the nickname the 'Goldilocks zone' after the children's story Goldilocks and the Three Bears in which the porridge is neither too hot nor too cold, but just right. As of October 2007, no such planets have been found.
New General Catalogue
The NGC catalogue was compiled by John Louis Emil Dreyer, the director of the Armagh Observatory from 1882 to 1916. Perseus is rich in open stellar clusters. M34 is particularly interesting for the not-so-well equipped stargazer. NGC 884 and NGC 869 are a very famous cluster pair. They are a marvellous sight in a small telescope. Don't magnify too much. They are better known as 'h Persei' and 'chi Persei'.
| Catalogue No | Name | Spectral classification | Brightness (m) | Distance (light years) | Notes |
| NGC 1039 | M34 | open cluster | 6 | 1,500 | +100 stars |
| NGC 650/651 | Little Dumbbell Nebula (M76) | Planetary nebula | 10 | 3,400-15,000 | aka Barbell Nebula |
| NGC 869 | Melotte 13 | open cluster | 4.5 | 6,800 | Double cluster with NGC 884 |
| NGC 884 | Melotte 14 | open cluster | 6 | 7,600 | First recorded by Hipparchus |
| NGC 1499 | California Nebula | Emission nebula | unknown | 1,000 | Illuminated by xi Persei |
| NGC 1275 | Perseus A | Seyfert galaxy | 12.6 | 250m | Merging with Perseus Cluster (Abell 426) |
| NGC 1333 | Unnamed | Reflection nebula | 10 | 1,000 | Less than a million years old |
Meteor Showers
Meteor showers occur when the Earth passes through the debris path left by the tail of a comet. There are two annual meteor showers called the Perseids - so named because they appear to originate from the constellation of Perseus. The earlier Perseids are probably the most famous meteor shower. You should watch out for them from 20 July to 19 August, with the maximum around 11 August. Their origin is Comet 1862 III.
New Look in 2007
Perseus does not look 'Perseus' familiar to us due to the bright stellar object now.
- Comet 17P/Holmes observer reporting from Japan.
The constellation Perseus took on a new 'look' in late 2007. An insignificant visitor to the inner Solar System, Comet 17P/Holmes takes just under seven years to orbit the Sun once. Barely worth a mention in newsprint, Comet 17P/Holmes suddenly became a media megastar in October 2007. Instead of being around 17th magnitude - only visible to powerful telescopes - it had an eruption, brightening the comet by a factor of a million, and became 3rd magnitude. The eruption could have been caused by a build-up of gas below the surface suddenly spewing out, or another space body could have impacted with it. Comet 17P/Holmes was passing through a particularly volatile place at the time, the Asteroid Belt, between the orbits of Mars and Jupiter, where there are lots of potential collisions. The eruption on the comet made it easy to spot with the unaided eye, even in cities with heavy light pollution.
Ancient cultures (the Chinese, in particular, thought comets were 'celestial ambassadors') would have had a field day with this comet's eruption, as comets have long been thought portents of momentous events. Comet 17P/Holmes was featured as Astronomy Picture of the Day's star-of-the-day for 3 November, 2007. The celestial firework was honoured again on 5 November when it displayed a green coma and blue tail. On 9 November Astronomy Picture of the Day published an image of the comet and the surrounding skyscape, showing the comet forming a triangle with alpha and delta Persei. On 19 November the comet passed directly in front of alpha Persei, Mirfak, changing the constellation's appearance once again.
