The constellation of Pegasus¹ the winged horse is easily definable. Imagine a line from Ursa Major to the Pole star then onto Cassiopeia, the great square of Pegasus follows on. The head of the horse is bent down towards the equator, extending to Cygnus and Delphinus.

The convention when referring to one celestial object in relation to another is to refer to it being North, South, East or West of it. To orientate yourself imagine you are standing with your back to North, looking South. East is to your left and West is to your right. Now look at the portion of sky just above the horizon. South is at the bottom of this piece of sky so North must be at the top (right up and over your head behind you). East is still to the left and West to the right. Therefore in this case, Pegasus being apparently to the right of Andromeda can be said to be West of it. For observers in the Southern Hemisphere the positions are reversed. North is now down and South is up, while East is now to the right and West to the left.

Mythology

There are two stories concerning the birth of Pegasus. In one version, Pegasus sprang to life from the blood of the Medusa which had just been killed by Perseus. The other story has the Medusa's blood spilling into the seafoam, Poseidon's domain, creating a demigod offspring.

The vain queen Cassiopeia offended the god of the oceans, Poseidon, when she boasted that her own and her daughter's beauty was greater than that of the sea nymphs, the Nereids, who were his handmaidens. Angry Poseidon sent storms to ravage the coast of their kingdom as punishment for the queen's vanity. To bring an end to the suffering, King Cepheus went to the Oracle of Ammon for advice and was told to sacrifice his daughter Andromeda to the sea monster Cetus, to placate Poseidon.

Andromeda was duly chained to the rocks on the coast for the sea monster to devour. She was saved at the last moment by the hero Perseus, riding in on his winged horse Pegasus. Later on, the goddess Athena (the favourite daughter of Zeus) gave Bellerophon a golden bridle which he used to capture Pegasus. With the flying horse at his command, Bellerophon was invincible; he even defeated the feared Chimera². Bellerophon went too far though, when he attempted to get Pegasus to take him to Mount Olympus, the realm of the gods, which was forbidden. Pegasus refused to obey and threw Bellerophon off his back, causing him severe injuries. Because Pegasus was mortal, at the end of his life he was placed in the heavens as a constellation by Zeus.

Another interesting story, before the International Astronomical Union (IAU) reclassified the constellations, concerns the four bright stars of the original Square of Pegasus. They were supposed to be King Diomedes' flesh-eating mares, the capture of which was the eighth of Hercules' 12 labours decreed by the Oracle of Delphi. Alexander the Great's famous mount Bucephalus, who really existed, was supposed to be descended from these mares.

Principal Stars

The scientific star names are simple to understand (if you know your Greek alphabet). 'Alpha Tau' means that it is the brightest star in the constellation Taurus. The next brightest is 'beta Tau', etc. Some stars have proper names as well; for example alpha Ori is known as Betelgeuse; others are known by their catalogue numbers or 'designation'.

The Great Square of Pegasus is easily recognisable. Three of the four corners are alpha Pegasi, Markab, in the south-west, which is the brightest star in Pegasus, gamma Pegasi, Algenib in the south-eastern corner, and beta Pegasi, Scheat, in the north-western. Scheat, a red giant, has a strong solar wind causing the star to be surrounded by a thin outer layer of gases. The fourth corner however presents one of those anomalies that occurs occasionally in the nomenclature of astronomy.

In 1930 the IAU decided to clear up the ambiguous borders to the constellations and set clearly defined limits for all of the 88 constellations. In doing so they allocated the north-eastern star of the square, Alpheratz, sometimes known as Schirra, to the neighbouring constellation of Andromeda. Up to that time Alpheratz had been classified delta Pegasi, but with this change was re-classified as alpha Andromedae. Another clearly identifying feature to the square is that Scheat is one corner of a triangle of stars; the other two, eta and mu Pegasi, lie outside the square to its western side.

Star Table

Extrasolar Planets

The planet orbiting 51 Pegasi is the first one found by the Doppler spectroscopy technique, in which a plan­et's gravita­t­ional pull is de­tected by the 'wob­ble' its gra­vity pro­duces in the par­ent star as it orbits. Designated 51 Pegasi b, it was the first extrasolar planet found to be orbiting a stable sun. Two others had been found previously but their parent stars were pulsars. The discovery of 51 Pegasi b was announced on 6 October, 1995, causing immense excitement through the field of astronomy. Bellerophon is the unofficial name this planet has been dubbed with, after the mythical captor of Pegasus. 51 Pegasi b is half Jupiter's mass³ but bigger in actual size. However it is extremely close to its star, a mere 7.5 million km (4.6m miles) distant, so its year only lasts 4.25 days. This orbit compares to around 13% of the orbital period of our innermost planet, Mercury.

A planet designated HD 209458 b orbiting yellow dwarf star HD 209458 (V376 Pegasi) was detected in November 1999. Astronomers found that the planet's atmosphere contains sodium. As the planet is in such close proximity to its sun, its atmosphere is literally boiling away into space, so it leaves a comet-like trail of blue-glowing energised hydrogen gas in its wake as it orbits the star. HD 209458 b has been given the unofficial name 'Osiris' until a proper catalogue name is decided upon.

Another extrasolar planet was discovered in April 2007 orbiting HD 210702, an orange subgiant. HD 210702 b is twice the mass of Jupiter but its orbital period (year) is 341 days. 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. 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 planet has been found.

New General Catalogue Objects

The NGC catalogue was compiled by John Louis Emil Dreyer, the director of the Armagh Observatory from 1882 to 1916. The numbers of NGC objects are based on the lowest Right Ascension co-ordinates appearing first. NGC 1 and NGC 2 both appear in the constellation Pegasus.

Stephan's Quintet is a set of five colliding galaxies, labelled NGC 7318 and NGC 7319 and NGC 7320. The whole cosmic dance provides a stunning view in small telescopes. Stephan's Quintet was featured on the BBC's monthly astronomy TV programme The Sky At Night in November 2007.

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 every July/August called the Pegasids, so named because they appear to originate from the constellation of Pegasus. The July Pegasids are typically active from 7 July for around a week. The Upsilon Pegasids commence around the end of July and last until the end of August.

Pegasus in Modern Culture

• There is a Pegasus Theatre in Oxford, UK.
• Pegasus is the name of the official car of the British Prime Minister. It's bullet-proof and bomb-proof.
• The Pegasus was the spaceship in the BBC TV series Space Odyssey: Voyage To The Planets.
• The Rolls-Royce Pegasus is a jet engine powering all versions of the Harrier military aircraft.
• The Pegasus Award is an American music award, usually in the science fiction genre.
• In the James Bond spoof Johnny English starring Rowan Atkinson, Pegasus is the head of MI7.
• Crossing the Canal de Caen à la Mer at the village of Bénouville, in Calvados, France, is the famous Pegasus Bridge.
• There is a Pegasus Bay on the east coast of the South Island of New Zealand, named after the vessel The Pegasus which surveyed the bay in 1809.
• The Ferranti Pegasus computer of 1955 is arguably the zenith of the British contribution to computer development, and with a decent claim to being the world's first business computer.