Cepheus, an otherwise unremarkable king, sits at the pantheon of the mythological royal family at the heart of the famous Andromeda-Perseus story. How did this faint constellation change the way we look at the universe?
Images of Cepheus
The Image:
Left: A constellation map of Cepheus (Image credit: Torsten Bronger at Wikimedia Commons, https://en.wikipedia.org/wiki/File:Cepheus _constellation_map.png, GNU Free Documentation license.)
Right: Public Domain Image: Cepheus in the robes of a Persian king, depicted in the Atlas Coelestis of John Flamsteed (1729)
This photo of the constellation Cepheus shows, enlarged in their true color, the main “naked eye” stars that make up the shape of the constellation. Image courtesy of https://www.scienceandart.com
The Facts
1. The Image of: King Cepheus, mythological King of Ancient Ethiopia and descendant of the nymph Io a favorite of Zeus.
2. Right Ascension: 22h
3. Declination: +70%
4. Genitive: Cephei
5. Symbolism: The King/King Cepheus
6. Area: 588 sq. deg. (27th)
7. Main stars: 7
8. Bayer/Flamsteed stars: 43
9. Stars with known planets: 1
10. Brightest star: α Cep (Alderamin) (2.44m)
11. Nearest star: Kruger 60 (13.15 ly)
12. Messier objects: 0
13. Meteor showers: None
14. Bordering constellations: Cygnus, Lacerta, Cassiopeia, Camelopardalis, Draco, Ursa Minor
15. Visibility: At latitudes between +90° and −10°
16. Best visible: At 21:00 (9 p.m.) during the month of November
Significant Astronomical Objects
1) δ Cephei: In 1784, John Goodricke found the star δ Cephei varied in luminosity between the magnitudes of 3.6 and 4.3 with a period of 5.4 days. In 1912, Henrietta Leavitt determined the existence of the period-luminosity relationship. This discovery allows us to more precisely measure the distance of globular clusters and galaxies, and forever changed our understanding of the universe.
2) NGC 188 is the closest open cluster to the celestial North Pole.
3) NGC 6946 (The Fireworks Galaxy) tops the supernova hit parade with eight such exploding stars – more than any other galaxy.
4) NGC 7538 – beside the more famous Bubble Nebula – contains the largest protostar discovered to date.
Mythological Background
1) Although a faint constellation, Cepheus stands out as the royal patron in the famous Andromeda story. His wife, Cassiopeia, brags about the beauty of their daughter Andromeda. This upsets Neptune, who sends Cetus to devour the family. Cepheus strikes a deal and saves the family by offering Andromeda as a sacrifice to Cetus. But, before the sea serpent can eat the princess, our hero Perseus, fresh from slaying the evil Medusa, arrives on the winged Pegasus to save the day. The tale goes on, but it doesn’t include any more constellations.
2) China associated this constellation with the Inner Throne of the Five Emporers.
3) Not all mythology has a kingly reference. Arabian nomads called this group of stars “Al Aghnām” (the sheep) while at least one Arab astronomer named it “Al Radif” (the follower).
Amazing Facts
1) Cepheus is one the circumpolar constellations because it can be seen by most of the northern hemisphere all year.
2) α Cephei was the Pole star in 21,000 BC and γ Cephei was the Pole Star in 19,000BC. α Cephei returns as the Pole star in 7500 AD.
3) The famous double star Krüger 60 sits near δ Cephei. This pair of 10th and 11th magnitude red dwarfs orbit each other every 44.6 years. Krüger 60 is named for German astronomer Adalbert Krüger who mistakenly thought two optical double stars, including Krüger 60, were a real double star. Years later, American astronomer S.W. Burnham discovered Krüger 60 actually did have a real double.
4) John Goodricke discovered δ Cephei at the age of 19. He would die two years later.
5) At the time of Henrietta Leavitt’s discovery of the period-luminosity relationship, astronomers did not know the galactic “nebula” they saw lay outside the boundaries of the Milky Way. It wasn’t until 1923 that Edwin Hubble conclusively proved for the first time one of these galactic “nebula” was indeed another galaxy – the Andromeda Galaxy. He did this only by discovering a Cepheid variable within the 2.2 million light year distant galaxy. Unfortunately, Henrietta Leavitt never saw the cosmological implications of her stellar discovery. She died in 1921.
References
The Illustrated Encyclopedia of Astronomy and Space, Ian Ridpath, Editor
Exploration of the Universe, Third Edition, George O.Abell
Elements of Astronomy, Al Ferghani
Star Names – Their Lore and Meaning, Richard Hinckley Allen
Metamorphoses, Ovid
https://en.wikipedia.org/wiki/Cepheus_(constellation)
