Dark Sky Wales Astronomer Martin Griffiths takes a look at the Night Sky in October 2016
The nights are now well drawn in and at the end of the month darkness comes early. The Autumn constellations dominate the sky and Summer fades as the milky way descends to the west. There are still plenty of things to see nevertheless as Autumn has a rich retinue of objects.
Moon in October:
New: 1st October
First quarter: 9th October
Full: 16th October
Last Quarter: 23rd October
Planets in October:
Mercury: Is past greatest western elongation but is still a faint morning object in the first half of the month, residing in Virgo and shining at magnitude -1 just before sunrise on the 14th. It is at superior conjunction on the 27th and not visible in later October.
Venus: Continues to rise out of the evening dusk and brightens toward the end of the month to mag -4.1. It is bright but low in the southwest after sunset.
Mars: Moves to Sagittarius by mid month and shines at a feeble 0.2 magnitude. It is still bright but past its best with a tiny disc only a few arc seconds across.
Jupiter: rises out of conjunction with the Sun and is a morning object in the constellation of Virgo shining at magnitude -1.7
Saturn: Is in Scorpius but is fading to a magnitude 0.5 by mid month and setting rapidly after sunset
Uranus: Is at opposition this month on the 15th October shining as a tiny 3.5 arc second disk at magnitude 5.7 and is at its best for this year.
Neptune: Is in Aquarius and is visible all night, and is just past opposition and shining dimly at magnitude 7.8 it still requires a telescope to see it well.
Meteor showers in October.
There are two notable showers this month. The first is the Draconids which have their peak on October 7/8th but an almost first quarter moon may drown out some faint meteors. This is an unpredictable shower associated with the comet Giacobini-Zinner which has a 6.6 year orbit around the sun. In 2011 the shower stormed up to 100 meteors per hour in the predawn sky but for most observers we will be lucky to see 5 per hour unless they storm again!
The second shower is the Orionids, associated with the famed Halley’s comet and they have their peak on the 20th/21st of October but are hampered by a gibbous moon going to last quarter in the predawn sky. They have a usual rate of about 20 meteors per hour but the waning moon may well block some of the fainter ones. Nevertheless, this is a fairly consistent shower and worth checking on.
Interesting Events in October
On the 19th October at 7.00am the waning moon passes just 0.3 degrees from the first magnitude star Aldebaran making a pleasing photo opportunity. On the 3rd of the month the crescent moon joins bright Venus in the southwest just after sunset.
On the 9th October the Moon reaches its most southerly point of the year and shines brightly in the constellation of Sagittarius.
On the 25th October the dwarf planet Ceres is at opposition and lies in the constellation of Cetus at RA 01H 59m and Dec -01.20
Constellation of the Month: Pegasus
The constellation of Pegasus, “The Winged Horse” is one of the most easily recognizable groups in the autumn sky, and is the signpost that will enable the observer to find other, fainter groups of the season. In legend, Pegasus was born from the blood of the gorgon Medusa after she had been slain by Perseus. The horse then took the hero flying back to his homeland, where along the way, Perseus encountered Andromeda chained to a rock, awaiting her fate at the hands of Cetus. After Perseus had rescued Andromeda and returned to his home, he took Pegasus to Mount Ida, where the horse could enjoy eternity, grazing under the kindly gaze of Zeus. Pegasus was eventually placed in the sky to complete the tale of the heroic Perseus, but the winged horse itself was immortal, and tales of its exploits continue throughout Greek mythology, until finally all history of it has become lost.
To the Celts this was the horse of Llyr, the sea god, a beautiful white charger that figured in many Celtic myths and still has marine associations – we call the whitecaps of the waves whitehorses. In the ancient Celtic world this constellation (and Andromeda on its back) represented the goddess Epona riding her white horse and is symbolized in the British landscape by the chalk figure of the white horse at Uffington. English tradition tells us that it was here that St George defeated the dragon; mummers plays re-enacted here in times past linked St George to the legend of Perseus and Andromeda; his white steed still stands on the hill as an effigy to this legend. Lady Godiva at Coventry also commemorates the relationship of white horses to ladies. Her ride through the city is a Christianized tale of Epona, Perseus and Andromeda and the celebration of femininity and fertility.
In the Welsh folk tale The Mabinogion, Rhiannon, the bride of Pwll, Lord of Dyfed rides a magical white horse. These myths prevail even in nursery rhymes; ladies and white horses such as Banbury Cross with its association with bells and rings refers again to ancient tales of fertility and licentiousness that have sky magic woven through.
Pegasus is made up of four principal stars that create the well know “Square of Pegasus”, the most dominant asterism of stars in the autumn sky. The neck and head of the horse are well marked with stars, ending in Epsilon Pegasi, a lovely red star called Enif, meaning the “Nose”. Pegasus was placed upside down in the sky, and to complete its discomfiture, its legs have been cut off to form the constellation of Andromeda. Pegasus contains a few deep sky objects of note that can be seen in binoculars or a small telescope.
The first such objects is the exquisite globular star cluster M 15, which can be found by taking a line from the “top” of the head northwards through Enif, and extending it by 4 degrees. It lies in a pleasing field of eighth magnitude stars and sparkles at magnitude 7. In binoculars it resembles a roundish cometary nucleus, but the view through a small telescope is wonderful, showing partial resolution into stars, especially around the edges of this radiant ball of light. M 15 is one of the best globular clusters in the northern sky, as it probably contains over 250,000 suns, lying at a di
stance of 42,000 light years.
In the northwest of the constellation can be found an excellent galaxy for small telescopes or even a good pair of binoculars. This is NGC 7331, at RA 22h 37m 06s Dec 34°25m; an Sb type spiral that has often been compared with the great Andromeda galaxy, M31 in form. It is an object of tenth magnitude with a relatively high surface brightness and can be viewed as an elongated blob of blue – white light. NGC 7331 lies over 40 million light years away, so may be quite a massive galaxy when compared to the luminosity of other spirals at similar distances. Several sup
ernova have been recorded in this galaxy, so it is worth checking regularly, as such objects
often outshine the galaxy within which they originate.
Pegasus contains one rather curious asterism, NGC 7772, a collection of seven faint stars that is not a true cluster, merely a line of sight apparition, lying within the southern bounds of the square. Observers with large telescopes should attempt to find a collection of galaxies close by NGC 7331, known as Stephan’s Quintet, as well as more than a dozen others in this rich field of extragalactic objects.
One of the first extrasolar planetary systems was found in Pegasus in 1995. Michele Mayor and Didier Queloz discovered line shifts in the spectrum of the star 51 Pegasi indicated a small, unseen companion. The planet is considered to be about half the mass of Jupiter and lies 0.5 AU away from its parent star. Since 1995, further investigation strongly suggests another planet in the system. It is also a model for the Hot Jupiter hypothesis as the planet may have formed beyond 5 AU of the star and through friction with an equatorial disc extending from 51 Pegasi, may have wandered in to its present position. Note the golden colour of this star and ponder the significance of this beatiful system.