Dark Sky Wales Astronomer Martin Griffiths takes a look at the Night Sky in November 2018
The winter stars are now appearing in early evening whilst the Autumn constellations dominate overhead. The summer constellations are still fading and the Milky Way is becoming a fond memory until we see it again in springtime.
Moon in November:
New: 7th November
First quarter: 15th November
Full: 23rd November
Last Quarter: 30th November
Planets in November:
Mercury: Is at greatest eastern elongation on the 6th November and then moves toward the Sun to reach inferior conjunction on the 27th November.
Venus: Is in Virgo and is not well placed for observation in November as it rises, transits and sets in daylight.
Mars: is in Aquarius and is visible most of the evening, setting by midnight toward the month’s end. It shines brightly at magnitude -0.4.
Jupiter: Is in Libra and is not visible this month for Northern hemisphere observers as it is in conjunction with the Sun on the 26th November.
Saturn: is still in Sagittarius and sets by 20:30 by mid month. It can be seen as a 0.4 magnitude baleful yellow star.
Uranus: can be found as a faint star in the constellation of Aries, rising in the early evening and visible most of the night
Neptune: is past opposition and shines at magnitude 7.8. It is a telescopic object lying in Aquarius, setting in the early hours of the morning.
Meteor showers in November.
The Leonid meteor shower peaks this autumn on the night of the 17/18th November. Usually, this shower has a ZHR of about 25 meteors, but has storm activity every 33 years, the last time this happened was in 1999 when the parent comet of the Leonid stream, Comet Tempel-Tuttle last went around the Sun. There is no storm expected this year, and a 9 day moon may interfere with the brightness of some meteors, but keep an eye on the shower nevertheless.
The Southern Taurids reach their peak on the 5th of the month but this low grade shower has a ZHR of only 10 meteors per hour.
Interesting Events in November
On the 11th November, Saturn joins the moon with a separation of just 1.5 degrees. As the Moon moves eastward, by the 16th of the month, the Moon is just 1 degree south of the planet Mars.
Comets in November
In early December Comet 46P/Wirtanen will make its closest approach to the Sun and during November it may be visible just after dusk. The periodic comet, which orbits the Sun once every 5.4 years, was discovered in 1948. Its last close approach to Earth was in 2013, when it was 907 million kilometers from Earth. This year Wirtanen will come much closer and may get up to 3rd magnitude. Ephemerides are available at: http://www.cometwatch.co.uk/comet-46p-wirtanen/
Constellation of the Month: Cetus
Cetus is the largest constellation in terms of area in the autumn sky, and is an amorphous collection of faint stars that mark the boundaries of the fabled “Sea Monster” that was sent to attack the beautiful Andromeda to compensate for the boasting of her mother, queen Cassiopeia. Thankfully, the hero Perseus was on hand just in time to save the fair maiden. He killed the sea monster by showing it the decapitated head of the Gorgon Medusa, thus turning Cetus into stone. Poseidon, incensed that his monster was dead, placed it in the sky in a position where it could still threaten Andromeda, and roar its disapproval at Perseus. On old star maps, Cetus is always portrayed as a whale, with huge teeth, a dog’s head and generally frightful appearance, which belies the nature of these gentle creatures. Big, was obviously not always beautiful to the ancients.
Cetus contains a few objects of interest to the casual observer. Identifying the group is not difficult; simply look for the head of the monster, which is the most easterly part of the constellation. Its 5 stars mark out a round outline from which it is relatively easy to figure out the rest of the constellation as it spreads south and westwards. Cetus contains the beautiful variable star Omicron Ceti or “Mira”, the typical object of this type of celestial wonder, in addition to several galaxies that lie within the range of amateur telescopes.
The best deep sky object in Cetus is the Sb type spiral galaxy M 77, a tenth magnitude smudge of light just under the “chin” of the monster. It is not an easy object in binoculars, but it may be seen on a good night as a faint glowing mass of grey light 60 million light years away. M 77 is a very unusual galaxy, one of the closest of a type known as “Seyfert galaxies”, after the astronomer Carl Seyfert who made a study of their ultraviolet excess and their violent nuclei in the 1940’s.
Seyfert galaxies are mostly spiral types characterised by very bright nuclei in proportion to their spiral arms, and also the peculiar presence of emission lines in their spectra. Further study of these galaxies has revealed that there is a tremendous amount of energy flowing out of the core of these objects, originating from a very small space at the centre. They are also radio galaxies, and some are also visible in both x-rays and ultraviolet light, evidence of intense activity, the source of which is postulated to be a Black Hole. Astronomers think that a black hole of several million solar masses is shredding stars and gas within these galactic nuclei, and ejecting some of it into space where it collides with the intergalactic medium, creating a shock wave that causes such intense radiation. Seyfert galaxies are thus related to radio galaxies and Quasars, being a little lower down the energy scale.
Galaxies worth seeking out are NGC 157 and NGC 908; two galaxies with a magnitude of 11 so don’t expect to see them that well as in a small telescope they will merely be little smudges of light, and all but invisible in binoculars. NGC 157 is an Sc type spiral lying 65 million light years away, which looks a little elongated in a low power eyepiece. NGC 908 is an Sc type spiral at a similar distance to NGC 157 and is a little fainter than it. Both galaxies these can be viewed but their arms will be a dull haze with a faint core.
The flagship of the constellation is of course the beautiful red giant star Omicron Ceti, or Mira as it is commonly known. Hevelius named the star and it was the only variable star known for quite some period of time. The name means “Wonderful”, and many observers will agree that it deserves its name. Mira can be seen on any autumn night even when at minimum as it varies between magnitude 4 and magnitude 9 in a period of 331 days.
On occasion, Mira becomes a lot brighter even shining at second magnitude and can transform the autumn sky with its incredible orange glow. The spectral type is M, and the distance is roughly 300 light years, which is relatively close for such a star. Over 4000 Mira type long period variables are known, most of which have periods between 250 and 400 days, thus making convenient distance indicators, as most of these giant stars have a similar intrinsic luminosity.
Mira is a very large star, probably around 300 times the diameter of our Sun, and one of only three stars in which spectral bands of water vapour have been found. At minima, the star switches most of its energy output into the infra-red part of the spectrum as it becomes an intense red colour and the surface temperature drops to only 1800 degrees Kelvin. Its oscillations can be followed in binoculars or a small telescope and is an ideal object to introduce the amateur to the vagaries of variable star observing. It is also a binary system with a red giant companion. The star is moving through space and leaving a trail of gas behind it as some mass is lost from the system, something that is typical of such large red giants.
One star of interest within Cetus is the third magnitude Tau Ceti. It is not a binary system or variable, but is a G type star of almost the same dimension and luminosity as our Sun. Tau Ceti is only 11 light years away, and due to its Sun like qualities was picked as a target for the SETI programme, the search for extraterrestrial life. In 2012 it was postulated that this star has a planetary system, with some researchers describing a 5-planet system with one planet in the habitable zone – and area where liquid water could exist on the planetary surface. No telescope yet built will show these planets however, so we will have to await any reply to our radio signals to confirm their presence. As yet no one has answered.
One lovely planetary nebula worth noting is NGC 246, the “skull nebula” at RA 00h 47m 18s Dec -11.52m.18s. It is a large nebula that is almost 4 minutes in diameter and shines at 10th magnitude and looks a little like “Pac-man” from the computer game. Cetus contains little else of interest to the observer with modest equipment, although owners of large telescopes will have a red letter day with the dozens of galaxies visible in this area, most of which are around 12th magnitude and are good candidates for the scrutiny of the supernova patrol. Browsing through a good star atlas will give their positions against the star of this large constellation.