Observing

  • 01-10-2014

    Stargazing in December 2014

    The December Night Sky

    The General Weather patterns

    December weather is likely to be rain and drizzle, and westerly storms, heavy rain can persist. On the other-hand it can be very cold, but usually not for very long, just a prelude to the freezing winter temperatures to come.

    From Earth

    The Winter Solstice occurs at just about 04:40 on the morning of the 22nd, and this is therefore the longest night. Sunset varies by no more than ten minutes throughout the month. And at the end of December, the Sun nudges its way, ever so slightly, towards more northerly celestial latitudes. Day now encroaches on night

    The Sun

    In keeping with the equation of time the earliest sunset is around the 12th December in South Wales, and the latest sunrise is around the 30th this year.

    The Sun moves over from Ophiuchus on the 17th and remains in Sagittarius for the rest of the month. The Sun is no higher than 15º above the horizon at this time of year and is seen through much more atmosphere at noon than at any other time of the year. All other things being equal, this is not best time of year for solar observing from the UK. Forgive me for constantly reminding you that sunlight is so very harmful to our eyes, a safe method of observing should be used, even with such a low Sun.

    The Moon


    The First Quarter is on 7th at about 09:05 in the constellation of Aquarius.

    The Full Moon is on 14th at about 00:05 in the constellation of Gemini.

    The Last Quarter is on 21st at about 01:55 in the constellation of Virgo.

    The New Moon is on 29th at about 06:55 in the constellation of Sagittarius.

    The Moon is at perigee (nearest Earth) on the 12th in the constellation of Taurus and at apogee (most distant from Earth) on the 25th in the constellation of Libra.

    The lunar occultation of some stars in the Hyades takes place on the night of the 12/13th, starting with γ Tauri at 21:37.and ending with the occultation of Aldebaran between 05:23 and 05:54 as seen from Usk. This will be one of the delights of the month for those dedicated observers who stay up for it!

    The Planets

    Mercury -- is at greatest eastern elongation on the 11th and sets just over an hour after the Sun. Mercury is below the ecliptic at this time, and is low down by the time it gets dark enough to observe. However during this presentation, the next few days are the best time to observe Mercury for it then quickly moves to inferior conjunction on the 28th. Allow the Sun to set before attempting to observe it.

    Venus -- is best observed late in the month when its altitude is greatest. At this time of year the ecliptic at sunset steepens significantly, increasing the altitude at which planets in the western sky can be found. Venus shines brightly in the south-south-west, observe it with a telescope as soon as the Sun is safely out of the way. A thin crescent Moon joins Venus and Mars on the morning of the 31st for a lovely photo-opportunity just after sunset.

    Mars -- advances from Capricornus into Aquarius in the middle of the month and gains more height at sunset in the south-south-west as the month progresses. As Mars drops further behind us in its orbit around the Sun, its magnitude continues to diminish below +0.89.

    Jupiter -- can be found in Virgo throughout the month; rising steeply at 03:00 at the start of December. By the end it rises at 01:30 and culminates in the dawn twilight, an hour or so before which is the best time to see it. Jupiter will be at opposition in April so will continue to improve for casual observers.

    Saturn -- is in Ophiuchus throughout this month but is joined on the 10th by the Sun; it is in conjunction. As such, it is best to ignore it in December, and observed it in the 2017.

    Uranus -- is visible throughout the evenings of December and is well placed to observe, the best time to view it is early December. At a magnitude of 5.74 it may well be seen with binoculars. A decent quality small telescope might show a blue hue, but since Uranus usually has few features, little else may be seen even with a larger amateur instrument, as demonstrated by Nick Busby in November. Uranus can be found culminating at around 19:50 in the constellation of Pisces at RA 1h 17m 11s, Declination 7º 29' 23", in the middle of the month.

    Neptune -- is also visible in the early evening during December and is well placed to observe. In the middle of the month at around 17:20, it can be found culminating in the constellation of Aquarius at RA 22h 45m 19s, Declination -8º 49' 40". It has a magnitude of 7.91and may just be visible using binoculars, but a decent quality small telescope would be better. Neptune is best observed in early December.

    Meteors

    The maximum of the Puppid-Velid meteor showers occurs in the mornings of December 8th and 25th. With a ZHR of about 15 per hour, these particular meteor showers may only be visible to those far enough south to see the constellation of Puppis. In Spain or Portugal it is just above the horizon. Viewing will be possible all night long although Puppis is highest in the south after 2:00. Most of the meteors are faint and the radiant is very low, this shower is known to produce an occasional fireball.

    The Geminids one of the most hauntingly beautiful displays of celestial fireworks, are associated with the minor planet Phaethon and can be seen from the 8th to 17th December with a ZHR ~ 50 to 120. It is generally the most splendid shower of the year, and can be rich in fireballs, though most are slow meteors with a radiant in Gemini. It is best observed around 20:00 on the 13th this year, but because the full Moon is only four hours later in Taurus it is unfavourable.

    The Ursids are associated with Comet 1926 IV P/Tuttle, and can be seen from the 17th to 25th December. This shower is quite weak with a ZHR ~ 5 but in some years occasionally ~ 50. This year the maximum is around the 22nd/23rd from a radiant near Kochab in Ursa Minor, and is favourable with the 23 day old crescent Moon rising at approximately 02:00.


    Perseus (Pronounced PER-see-us)

    Perseus reaches its highest point before 21:00 in the evening sky in late December when it is at the zenith. It is a northern constellation lying east of Andromeda and north-west of Taurus. It contains the bright star Mirfak (MERE-fak) (α Persei) some 620 light-years away, which appears to be surrounded by a large, sprawling star cluster (not commonly recognised as an open cluster). Mirfak's name derives from the Arabic Al-Mirfaq which means ‘The Elbow’ of the Pleiades. Its visual magnitude is a bright 1.8 whilst Algol (b Persei), has a variable visual magnitude of 2.1 to 3.4. Algol (AL-gall) is a bright, eclipsing binary star. Its name derives from the Arabic Ra's Al Ghul, the ‘Demon's Head’. The Arabic ghul means a demon or mischief-maker (origin of ghoul). Some suggest Algol is the eye of Medusa, the gorgon beheaded by Perseus.


    A feature of note is a smudge of light located in the upper part of Perseus, almost into Cassiopeia. This is the double cluster in Perseus (NGC 869 and NGC 884). These young clusters of stars are moving through space together, averaging 7500 light-years away; they are just barely visible to the naked eye to the south-east of the "W" of Cassiopeia. A pair of binoculars will reveal their true character, a pair of interacting clusters of stars.

    A meteor shower known as the Perseids appears to radiate from near the double Cluster; this shower can be seen every year for at least a week either side of August 12th, but is best seen between 9th and 14th August, after midnight. It has a ZHR ~ 75 and is associated with Comet P/Swift-Tuttle.

    In 1901 a brilliant nova (GK Per) was observed in the constellation, and left the magnificent 'firework' nebula, this nebula shows unusual features, probably as it expanded into interstellar material much denser than usual.

    Myths

    Greek

    Perseus's whole life was one of drama, intrigue and tragedy. He was the son of the god Zeus (hence per Zeus), and Danae, the beautiful daughter of Acrisius, King of Argos. Now Acrisius had kept his daughter hidden for many years, fearful of an oracle that foretold his death at the hands of her son. To gain access to Danae, Zeus had turned himself into a shower of gold dust in order to enter to her underground prison, and she became pregnant. Fearful of his fate, Acrisius set mother and child adrift on the sea in a wooden chest, but a fisherman at Seriphos, in the Aegean Sea, rescued them and took them to his king, Polydectes. They remained with Polydectes until Perseus reached manhood. Then, in order to rid himself of Perseus so that he could force his attentions on the beautiful Danae, Polydectes sent Perseus on an 'impossible' mission to slay the Gorgon Medusa who had snakes for hair. Anyone who looked directly at her would be turned to stone.

    The Olympian gods decided to help him. Athena gave him a polished bronze shield and Hermes awarded him winged sandals. Hephaestus presented him with a gleaming sword made of diamond. With this help he beheaded Medusa by looking at her reflection in the shield.

    After completing his mission Perseus flew home in magical winged slippers that he had acquired to help him on his mission, but was blown in every direction by fierce winds until he reached the realm of the mighty Atlas at the western edge of the world. Exhausted by his endeavours and his stormy journey Perseus requested rest and nourishment from Atlas but was refused.

    He took Medusa’s head from its bag and showed it to the mighty Atlas, who promptly turned into a gigantic mountain, growing until the very heavens rested on his head or summit.

    At dawn the stormy winds that had dogged Perseus's journey subsided and Perseus continued on his flight when he found and rescued the beautiful Andromeda from being eaten by the sea monster Cetus. Andromeda was chained to the rocks by her father in atonement to Poseidon; the god of the sea, after her mother, Cassiopeia claimed that she and Andromeda were more beautiful even than the sea nymphs, the Nereids. Some say that Perseus rode Pegasus to rescue Andromeda.

    On his return to Seriphos, Perseus took revenge on Polydectes and his court, turning them to stone also with the gorgon’s head.

    Later Perseus returned to Argos where he played a game of quoits with his grandfather, and during the game he struck the old man on the foot with a badly thrown disc. The injury ultimately proved fatal and the oracle’s prophecy was unwittingly fulfilled.

    Myan

    Obviously, there are alternative ways to visualise this constellation. The Maya Indians described a snake in the sky, indicating that the stars we know as the Pleiades were the rattles of the snake and the body of the Maya snake was composed of the stars of what we call Perseus. Using the Pleiades as the rattles of a snake, you can follow the crooked line of stars in Perseus, the snake's body, along the Milky Way toward the W-shape of Cassiopeia. Right at the head of the snake is the wonderful double cluster; many hundreds of stars bunched together just waiting for you to look at them through binoculars.

    David J Thomas

    If you wish to download a copy of this months Night Sky News-letter please click here