Dark Sky Wales Astronomer Martin Griffiths once again looks at the night sky for the month ahead.
The winter is almost fully upon us and the constellations of Taurus Orion and Gemini are great features of the early nights. Perseus and Auriga climb high overhead and the bright star Sirius begins to dominate the late evening.
Moon in December:
New: 18th December
First quarter: 26th December
Full: 3rd December
Last Quarter: 10th December
Planets in December:
Mercury: is at greatest eastern elongation on the 24th November and then moves rapidly to inferior conjunction, coming between the Earth and Sun on the 13th December.
Venus: moves into Ophiuchus this month and is still a brilliant morning object shining at magnitude – 3.8 rising just before the Sun.
Mars: Continues to be an early morning object in the constellation of Virgo, rising before the Sun and shining dimly at magnitude 1.8.
Jupiter: is a morning object in Libra rising before the Sun and is a bright magnitude -1.5 object so should be immediately visible in the morning twilight.
Saturn: Is still in Ophiuchus but is too close to the Sun for good observations this month. It is in conjunction with the Sun on the 21st December.
Uranus: Is in Pisces and as a distant planet shines at magnitude 5.9 but still only subtends a small disk just under 4” across.
Neptune: The furthest planet from the Sun remains in Aquarius and rises in the evening shining at a miserable magnitude of 7.9. It has a very small 2” disc.
Meteor showers in December.
One of the best showers of the year, the Geminids will peak on the night of Dec. 13 and morning of Dec. 14. The Geminids are considered one of the best meteor showers every year because the individual meteors are bright, and the peak can see meteors stream across the sky at rates as high as 120 meteors an hour. Under light-polluted skies, fewer meteors will be visible.
The Ursids on the other hand are not well studied but have a peak of about 10 meteors per hour and this year will see their peak on the night of 23/24th December. A waxing crescent moon will be well out of the way to see the majority of these meteors.
Interesting Events in December
On the 3rd December and again on the 31st December, the Moon is very close to Aldebaran and occults some of the stars of the Hyades.
Comets in November
Comet ASASSN C/2017 O1 continues to move through Perseus and Auriga and is visible all night but is a faint 12th magnitude object that fades throughout the month.
Constellation of the Month: Eridanus
The constellation of Eridanus must be one of the most confusing constellations from an amateur point of view. Eridanus, “The River”, is not too difficult to pick out, in fact the star b Eridani lies fairly close to b Orionis, the brilliant Rigel whilst the rest of the constellation meanders in a line of faint stars south and westwards from this point, ending with the first magnitude star Achernar, which never rises in British climes.
In mythology, Eridanus is thought to be the river that the Earth disgorged to drown the rash youngster Phaeton, who thought he could control the chariot of the Sun that belonged to his father Apollo. Phaeton lost control of the chariot, and to prevent harm to the inhabitants of the Earth, the river claimed him, but not before he had given the inhabitants of the continent of Africa a crisp sun tan, and thus mythically accounted for their skin colour today. It has also been identified with the river Nile, and with the vanished river Gihon mentioned in the bible as one of the rivers in the Garden of Eden.
The area around b Eridani is dotted with faint galaxies, of which the Sc type NGC 1084, at RA 02h 46m 11s Dec -07°33m, is the brightest at magnitude 11.1. Close to b Eridani is the faint nebulae I.C. 2118, otherwise known as the “Witch Head” nebulae, and possibly illuminated by Rigel, but this object is beyond average equipment although it may prove fruitful as a photographic target.
Despite the fact that there is little of interest to the deep sky observer, there are several stars worth noting in the sprawl of this ancient constellation. o Eridani is a relatively close star to our own system and is a beautiful triple star. Additionally, this system contains one of the best white dwarf stars visible in a small telescope. Both companions of o Eridani are dwarf stars, one is the white dwarf mentioned above and the other is a lovely contrasting red dwarf. The magnitudes of these stars are 9.7 for the white dwarf and 10.8 for the red dwarf, whilst the primary star shines at magnitude 4.8, making it an easy naked eye object.
NGC 1535 is a beautiful planetary nebula which can be found at RA: 04h 14m 12s Dec -12°44m. It is a slightly oval, filled ring of turquoise light of 9th magnitude and is instantly visible in the field as the position is quite far from the Milky Way. NGC 1535 takes a little effort to hop to, but the effort is well rewarded.
e Eridani is one of the closest stars to Earth, and is a star that is remarkably close to the Sun in type, although it has about a third of the Sun’s mass. It has been the target of enthusiastic professional astronomers searching for other life forms, as its Sun like characteristics are held to be a good omen for alternative intelligent beings. This star underwent intensive “listening” studies in the S.E.T.I. program during the late 1970’s, but if anyone is out there, they have yet to signal their presence. The star is only 10.5 LY away and is visible near Orion’s Belt. In 1998 it was found to have one Jupiter-like planet and the system is undergoing further scrutiny in order to discover any others.
Many of the faint stars in Eridanus are relatively nearby objects, some lying within a 25 light year range. The future of the human race may lie amongst the commonplace stars of this unusual constellation; they are close enough to be stepping-stones to the rest of our galaxy when our technology catches up with our dreams. On a planet circling e Eridani, perhaps intelligent life forms not too different from us are similarly contemplating the beauty of our universe, and wondering “is there anybody out there?”
Dark Sky Wales provide guided tours of the night sky with Martin and Allan as your guides. For more information and to purchase a gift voucher take a look at our website http://darkskywalestrainingservices.co.uk/experiences-and-gift-vouchers/