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The Night Sky December 2009

Compiled by Ian Morison

This page, updated monthly, will let you know some of the things that you can look out for in the night sky. It lists the phases of the Moon, where you will see the naked-eye planets and describes some of the prominent constellations in the night sky during the month.

Image of the Month

V838 Mon

Light Echos around the star V838 in Monocerous
Image:Hubbel heritage team, NASA

This image by taken by the Hubble Telescope shows what are termed "Light Echos" surrounding the star V838 that lies in the constellation Monoceros.  On January 10th, 2002, it suddenly expanded and, for a short while, became one of the brightest star in the galaxy. It was then ~1,000,000 times brighter than our Sun!   The flash of light expands out at the speed of light so will then illuminate regions of the dust cloud in which V838 is embedded.  The set of images taken by the HST shows how succesively more distant regions of the dust cloud were illuminated over the next two years.  The final image was taken just over 2 years later, so the "dust ring" diameter must be ~4 light years across.  As we know the angular size of the ring it is then easy to calculate its distance from us - which is ~20,000 light years.

Highlights of the Month

December 14th after midnight: a great year to look out for the Geminid Meteor Shower!

Dec14th
Image:Stellarium/IM

The Geminids

The early morning of December 14th will give us the chance, if clear, of observing the peak of the Geminid meteor shower.  Happily, this year, the Moon is just two days before full moon and so its light will not intrude!  You could see more that 60 meteors an hour in the early hours of the morning when Gemini is high in the sky!  An observing location well away from twos or cities will really pay dividends though.   The relatively slow moving meteors arise from debris released from the asteroid 3200 Phaethon.  This is unusual, as most meteor showers come from comets. The radiant - where the meteors appear to come from - is close to the bright star Castor in the constellation Gemini as shown on the chart above. If it is clear it will be cold - so wrap up well, wear a woolly hat and have some hot drinks with you. These could be perfect conditions fow viewing one of the best annual meteor showers, so do try if the skies are clear.  There is usually some activity from this shower during the preceeding week so its also worth a look then if clear, though the Moon will be more prominent in the sky.

December 31st: A Partial Eclipse of the Moon (just)

Lunar Eclipse
Partial Lunar Eclipse on December 31st.
Image: Stellarium/IM

In the early evening of the 31st December the Moon undergoes the smallest partial eclipse that we have seen in the UK for 40 years - in that the Moon will only just dip into the umbral shadow of the Earth. At mid-eclipse (19:23) the lower right of the Moon may just be seen to have a faint ruddy colour as indicated in the diagram.  The Moon begins to enter the penumbral shadow at 17:17, and will thus begin to darken.  A small part of the Moon at its lower right enters the umbral shadow at 18:52 and leaves it at 19:52 with mid-eclipse being at at 19:23. Incidently, this is a "Blue Moon" - the name now given for the second full-moon within a calender month though originally the definition was somewhat more complex.

Around new Moon ~16th December: Find Uranus.

Uranus
Chart showing position of Uranus
Image: Stellarium/IM

Uranus was at opposition on September 17th and is still well placed to observe in the evening. With a magnitude of +5.7 it lies just below the circlet of Pisces which itself lies below the square of Pegasus  On the 1st December it lies 5 degrees below and a little to the left of the star Kappa Piscoris as shown on the chart.  Under very dark skies it would just be visible to the unaided eye, but binoculars will probably be needed to see it from our light polluted skies.  If Kappa Piscoris is put at the upper right of the field of view, you should see Uranus at the bottom of the field.

Find M31 - The Andromeda Galaxy and, perhaps, M33 in Triangulum

M31
How to find M31 and M33
Image: Stellarium/IM

In the evening, the galaxy M31 in Andromeda is visible high in the south. The chart provides two ways of finding it:

1) Find the square of Pegasus. Start at the top left star of the square - Alpha Andromedae - and move two stars to the left and up a bit. Then turn 90 degrees to the right, move up to one reasonably bright star and continue a similar distance in the same direction. You should easily spot M31 with binoculars and, if there is a dark sky, you can even see it with your unaided eye. The photons that are falling on your retina left Andromeda well over two million years ago!

2) You can also find M31 by following the "arrow" made by the three rightmost bright stars of Cassiopeia down to the lower right as shown on the chart.  

M33: Having found M31, if you backtrack to the star where you turned sharp right and continue on for the same distance you may be able to spot the face on spiral galaxy, M33 in Triangulum if the skies are very dark and transparent.  Binoculars will only show it as a faint smudge against the darker sky background.  Sadly, quite a large telescope is required to see any detail.   Good Hunting!

December 21st: Jupiter, Neptune and the Crescent Moon

Jupiter
Jupiter, Neptune and the 23 day old Moon
Image: Stellarium/IM

At about 7-8pm on the 21st December,the Moon, a day before first quarter, is just over 3 degrees up to the right of Jupiter. Neptune, at magnitude 7.9, lies between them and is just 0.6 degrees to the upper right of Jupiter.  It lies just to the left of a line of three stars, 42 Cap, the upper, at 5.1 magnitude, 44 and 45 Cap, below at ~ 6th magnitude. A pair of 8 x 40 binoculars should be able to encompass the field of view. Neptune will be easier to spot on the days before and after when the Moon is not so close in the sky.

Observe the International Space Station

The International Space Station
The International Space Station and Jules Verne passing behind the Lovell Telescope on April 1st 2008.
Image by Andrew Greenwood

Use the link below to find when the space station will be visible in the next few days. In general, the space station can be seen either in the hour or so before dawn or the hour or so after sunset - this is because it is dark and yet the Sun is not too far below the horizon so that it can light up the space station. As the orbit only just gets up the the latitude of the UK it will usually be seen to the south, and is only visible for a minute or so at each sighting. Note that as it is in low-earth orbit the sighting details vary quite considerably across the UK. The NASA website linked to below gives details for several cities in the UK. (Across the world too for foreign visitors to this web page.)

Note: I observed the ISS three times recently and was amazed as to how bright it has become.

Find details of sighting possibilities from your location from: Location Index

See where the space station is now: Current Position

The Moon

3rd Quarter Moon
The Moon at 3rd Quarter. Image, by Ian Morison, taken with a 150mm Maksutov-Newtonian and Canon G7.
Just below the crator Plato seen near the top of the image is the mountain "Mons Piton". It casts a long shadow across the maria from which one can calculate its height - about 6800ft or 2250m.
new moon first quarter full moon last quarter
December 16th December 24th December 2nd/31st December 9th

Some Lunar Images by Ian Morison, Jodrell Bank Observatory: Lunar Images

A World Record Lunar Image

World record Lunar Image
The 9 day old Moon.

To mark International Year of Astronomy, a team of british astronomers have made the largest lunar image in history and gained a place in the Guinness Book of Records! The whole image comprises 87.4 megapixels with a Moon diameter of 9550 pixels. This allows details as small as 1km across to be discerned! The superb quality of the image is shown by the detail below of Plato and the Alpine Valley. Craterlets are seen on the floor of Plato and the rille along the centre of the Alpine valley is clearly visible. The image quality is staggering! The team of Damian Peach, Pete lawrence, Dave Tyler, Bruce Kingsley, Nick Smith, Nick Howes, Trevor Little, David Mason, Mark and Lee Irvine with technical support from Ninian Boyle captured the video sequences from which 288 individual mozaic panes were produced. These were then stitched together to form the lunar image.

Please follow the link to go to the website and it would be really great if you could donate to Sir Patrick Moore's chosen charity to either download a full resolution image or purchase a print.

Plato and the Alpine valley
Plato and the Alpine Valley.

The Lunar World Record 2009: Lunar World Record

The Planets

 A montage of the Solar System
A montage of the Solar System. JPL / Nasa

Jupiter

Jupiter
A Cassini image of Jupiter . Nasa

Jupiter, now lying in Capricornus, is still easily visible in the south-west after sunset. During December, its magnitude drops very slightly; from -2.2 to -2.1. It has an angular size of 37.3 arc seconds at the beginning of the month so a small telescope will show much detail on the surface if seeing conditions are good.  It is moving towards Neptune which is just 0.6 degrees away to the north on the 20th of the month.  On the 21st, a thin waxing crescent Moon will pass just three degrees above them. One problem with observing Jupiter with a telescope when it is so low in the sky is refraction in the atmosphere. This shifts the different colours of light in Jupiters image by differing amounts, so giving a blurred image. Using a green filter will help considerably in giving a cleaner image - and also making the equatorial bands more prominent.  I have even used a very narrow band OIII filter to observe Jupiter in monochromatic light giving excellent results - but needing a relatively large telescope to collect sufficient light. See also highlight above.

Saturn

Saturn
The planet Saturn. Cassini - Nasa

Saturn can now be seen in the pre-dawn sky when, as December begins and at magnitude +1, it will rise at about 01:30 UT.  By December's end it will be rising at 11:30 UT and so will be high in the South before sunrise. The angular size of the disc increases from 17 to 18 arc seconds during the month.  The ring system is still close to edge on (its tilt angle increases from 4.3 to 4.9 degrees during the month) and so will appear very thin - the reason why Saturn is not a bright as it is when the rings are more open. A small telescope will easily show its brightest satellite, Titan at magnitude 7.8, and one of 8 inches or more aperture several more.

Mercury

Mercury.
Messenger image of Mercury Nasa

Mercury reappears into the evening sky in the latter part of December and may then be spotted low above a clear southwestern horizon.  It reaches greatest elongation on December 20th when, at magnitude -0.5, a telescope will show a gibbous phase having an angular diameter of 6.7 arc seconds.  Observations around this date about 30 minutes after sunset should enable you to spot it, but binoculars will probably help!  If you get to your observing spot just before sunset, you will see in which direction to look - up and to the left of where the Sun's disc disapeared.  There is always a chance that you might see the "Green Flash" as the Sun finally sinks below the horizon - a green iridescent line along the horizon caused by refraction and absorption in the atmosphere.

See also highlight above.

Mars

Mars showing Syrtis major.
A Hubble Space Telescope image of Mars.
Jim Bell et al. AURA / STScI / Nasa

Mars is becoming prominent in the late evening sky, rising at about 20:30 UT at the begining of the month. It will be well up in the south-east by midnight and is due south and thus highest in the sky in the early hours of the morning.  It crosses from the constellation Cancer into Leo on the first of December and continues to move eastwards into Leo until December 20th when it begins its retrograde path westwards and returns into Cancer on January 9th.   This "retrograde motion" is because the Earth is overtaking Mars on the inside track.  Its magnitude increases from -0.1 to -0.6 during the month, whilst its angular size slowly increases from 10.2 to 12 arc seconds.  Under ideal seeing conditions, a telescope will now show some of the more prominent features such as Syrtis Major. The Earth continues to close on Mars "on the inside track" and thus its angular size will continue to increase for a month or so as we reach opposition at the end of January. Sadly, this apparition is not one of the best as, when we come between the Sun and Mars at opposition, Mars is towards the outer part of its elliptical orbit, so the angular size will only reach 14.1 arc seconds - in contrast to ~25 arc seconds at the very close approach a few years ago.

Venus

Venus
Venus showing some cloud structure

Venus. Somewhat to my surprise, I observed Venus just above the horizon on the 24th November.  The sky was very clear so the Sun's glare was not as obvious as usual.  On December 1st it rises 45 minutes before the Sun so you might just spot it, but Venus is then well on the way to Superior Conjunction (when it lies behind the Sun) on January 11th.  We will have to wait until the middle of February before we will have a reasonable chance of spotting it in the evening sky after sunset.

If you have the free program Stellarium (just put Stellarium into Google to find a download page) you can easily find when Superior Conjunction is by setting the time to ~12 noon UT, turning off the atmosphere (so you can see where the planets are in daylight) and simply adjusting the date until the planet in question is behind, just above or just below the Sun. Simples!

Radar Image of Venus
Radar image showing surface features

Find more planetary images and details about the Solar System: The Solar System

The Stars

The Early Evening December Sky

Early Evening December Sky
The December Sky in the south - early evening

The Late Evening December Sky

Late Evening December Sky
The December Sky in the south - late evening

This maps shows the constellations seen towards the south in early and late evening. Setting towards the west in early evening is the beautiful region of the Milky Way containing both Cygnus and Lyra. Below is Aquilla. The three bright stars Deneb (in Cygnus), Vega (in Lyra) and Altair (in Aquila) make up the "Summer Triangle". East of Cygnus is the great square of Pegasus - adjacent to Andromeda in which lies M31, the Andromeda Nebula. To the north lies "w" shaped Cassiopeia and Perseus. The lower map shoesthe constellation Taurus, with its two lovely clusters, the Hyades and the Pleaides, and is also described in more detail below. as the evening draws on, Orion, the Hunter, follows Taurus into the eastern sky with the constellations Auriga, above, and Gemini, to the upper left. Later Sirius, in Canis Major will be seen to the lower left of Orion. Due to its brightness and scintillations caused by the atmosphere it often appears as a rainbow of colours flashing in the sky.

The constellations Lyra and Cygnus

Cygnus and Lyra
Lyra and Cygnus

This month the constellations Lyra and Cygnus are seen almost overhead as darkness falls with their bright stars Vega, in Lyra, and Deneb, in Cygnus, making up the "summer triangle" of bright stars with Altair in the constellation Aquila below. (see sky chart above)

Lyra

Lyra is dominated by its brightest star Vega, the fifth brightest star in the sky. It is a blue-white star having a magnitude of 0.03, and lies 26 light years away. It weighs three times more than the Sun and is about 50 times brighter. It is thus burning up its nuclear fuel at a greater rate than the Sun and so will shine for a correspondingly shorter time. Vega is much younger than the Sun, perhaps only a few hundred million years old, and is surrounded by a cold,dark disc of dust in which an embryonic solar system is being formed!

There is a lovely double star called Epsilon Lyrae up and to the left of Vega. A pair of binoculars will show them up easily - you might even see them both with your unaided eye. In fact a telescope, provided the atmosphere is calm, shows that each of the two stars that you can see is a double star as well so it is called the double double!

The Double Double
Epsilon Lyra - The Double Double

Between Beta and Gamma Lyra lies a beautiful object called the Ring Nebula. It is the 57th object in the Messier Catalogue and so is also called M57. Such objects are called planetary nebulae as in a telescope they show a disc, rather like a planet. But in fact they are the remnants of stars, similar to our Sun, that have come to the end of their life and have blown off a shell of dust and gas around them. The Ring Nebula looks like a greenish smoke ring in a small telescope, but is not as impressive as it is shown in photographs in which you can also see the faint central "white dwarf" star which is the core of the original star which has collapsed down to about the size of the Earth. Still very hot this shines with a blue-white colour, but is cooling down and will eventually become dark and invisible - a "black dwarf"! Do click on the image below to see the large version - its wonderful!

M57 - The Ring Nebula
M57 - the Ring Nebula
Image: Hubble Space telescope

M56 is an 8th magnitude Globular Cluster visible in binoculars roughly half way between Alberio (the head of the Swan) and Gamma Lyrae. It is 33,000 light years away and has a diameter of about 60 light years. It was first seen by Charles Messier in 1779 and became the 56th entry into his catalogue.

M56 - Globular Cluster
M56 - Globular Cluster

Cygnus

Cygnus, the Swan, is sometimes called the "Northern Cross" as it has a distinctive cross shape, but we normally think of it as a flying Swan. Deneb,the arabic word for "tail", is a 1.3 magnitude star which marks the tail of the swan. It is nearly 2000 light years away and appears so bright only because it gives out around 80,000 times as much light as our Sun. In fact if Deneb where as close as the brightest star in the northern sky, Sirius, it would appear as brilliant as the half moon and the sky would never be really dark when it was above the horizon!

The star, Albireo, which marks the head of the Swan is much fainter, but a beautiful sight in a small telescope. This shows that Albireo is made of two stars, amber and blue-green, which provide a wonderful colour contrast. With magnitudes 3.1 and 5.1 they are regarded as the most beautiful double star that can be seen in the sky.

Alberio
Alberio: Diagram showing the colours and relative brightnesses

Cygnus lies along the line of the Milky Way, the disk of our own Galaxy, and provides a wealth of stars and clusters to observe. Just to the left of the line joining Deneb and Sadr, the star at the centre of the outstretched wings, you may, under very clear dark skys, see a region which is darker than the surroundings. This is called the Cygnus Rift and is caused by the obscuration of light from distant stars by a lane of dust in our local spiral arm. the dust comes from elements such as carbon which have been built up in stars and ejected into space in explosions that give rise to objects such as the planetary nebula M57 described above.

There is a beautiful region of nebulosity up and to the left of Deneb which is visible with binoculars in a very dark and clear sky. Photographs show an outline that looks like North America - hence its name the North America Nebula. Just to its right is a less bright region that looks like a Pelican, with a long beak and dark eye, so not surprisingly this is called the Pelican Nebula. The photograph below shows them well.

The North American Nebula
The North American Nebula

Brocchi's Cluster An easy object to spot with binoculars in Gygnus is "Brocchi's Cluster", often called "The Coathanger",although it appears upside down in the sky! Follow down the neck of the swan to the star Alberio, then sweep down and to its lower left. You should easily spot it against the dark dust lane behind.

The Coathanger
Brocchi's Cluster - The Coathanger

The constellations Pegasus and Andromeda

Pegasus and Andromeda
Pegasus and Andromeda

Pegasus

The Square of Pegasus is in the south during the evening and forms the body of the winged horse. The square is marked by 4 stars of 2nd and 3rd magnitude, with the top left hand one actually forming part of the constellation Andromeda. The sides of the square are almost 15 degrees across, about the width of a clentched fist, but it contains few stars visibe to the naked eye. If you can see 5 then you know that the sky is both dark and transparent! Three stars drop down to the right of the bottom right hand corner of the square marked by Alpha Pegasi, Markab. A brighter star Epsilon Pegasi is then a little up to the right, at 2nd magnitude the brightest star in this part of the sky. A little further up and to the right is the Globular Cluster M15. It is just too faint to be seen with the naked eye, but binoculars show it clearly as a fuzzy patch of light just to the right of a 6th magnitude star.

Andromeda

The stars of Andromeda arc up and to the left of the top left star of the square, Sirra or Alpha Andromedae. The most dramatic object in this constellation is M31, the Andromeda Nebula. It is a great spiral galaxy, similar to, but somewhat larger than, our galaxy and lies about 2.5 million light years from us. It can be seen with the naked eye as a faint elliptical glow as long as the sky is reasonably clear and dark. Move up and to the left two stars from Sirra, these are Pi amd Mu Andromedae. Then move your view through a rightangle to the right of Mu by about one field of view of a pair of binoculars and you should be able to see it easily. M31 contains about twice as many stars as our own galaxy, the Milky Way, and together they are the two largest members of our own Local Group of about 3 dozen galaxies.

M 31 - The Andromeda Nebula
M31 - The Andromeda Nebula

M33 in Triangulum

If, using something like 8 by 40 binoculars, you have seen M31 as described above, it might well be worth searching for M33 in Triangulum. Triangulum is

the small faint constellation just below Andromeda. Start on M31, drop down to Mu Andromedae and keep on going in the same direction by the same distance as you have moved from M31 to Mu Andromedae. Under excellent seeing conditions (ie., very dark and clear skies) you should be able to see what looks like a little piece of tissue paper stuck on the sky or a faint cloud. It appears to have uniform brightness and shows no structure. The shape is irregular in outline - by no means oval in shape and covers an area about twice the size of the Moon. It is said that it is just visible to the unaided eye, so it the most distant object in the Universe that the eye can see. The distance is now thought to be 3.0 Million light years - just greater than that of M31.

M33
M33 in triangulum - David Malin

The constellation Taurus

Taurus
Taurus

Taurus is one of the most beautiful constellations and you can almost imagine the Bull charging down to the left towards Orion. His face is delineated by the "V" shaped cluster of stars called the Hyades, his eye is the red giant star Aldebaran and the tips of his horns are shown by the stars beta and zeta Tauri. Although alpha Tauri, Aldebaran, appears to lie amongst the stars of the Hyades cluster it is, in fact, less than half their distance lying 68 light years away from us. It is around 40 times the diameter of our Sun and 100 times as bright.

The Hyades and Pleiades
The Hyiades and Pleiades. Copyright: Alson Wong.

More beautiful images by Alson Wong : Astrophotography by Alson Wong

To the upper right of Taurus lies the open cluster, M45, the Pleiades. Often called the Seven Sisters, it is one of the brightest and closest open clusters. The Pleiades cluster lies at a distance of 400 light years and contains over 3000 stars. The cluster, which is about 13 light years across, is moving towards the star Betelgeuse in Orion. Surrounding the brightest stars are seen blue reflection nebulae caused by reflected light from many small carbon grains. These relfection nebulae look blue as the dust grains scatter blue light more efficiently than red. The grains form part of a molecular cloud through which the cluster is currently passing. (Or, to be more precise, did 400 years ago!)

The Crab Nebula
VLT image of the Crab Nebula

Close to the tip of the left hand horn lies the Crab Nebula, also called M1 as it is the first entry of Charles Messier's catalogue of nebulous objects. Lying 6500 light years from the Sun, it is the remains of a giant star that was seen to explode as a supernova in the year 1056. It may just be glimpsed with binoculars on a very clear dark night and a telescope will show it as a misty blur of light.

The Crab Nebula
Lord Rosse's drawing of M1

Its name "The Crab Nebula" was given to it by the Third Earl of Rosse who observed it with the 72 inch reflector at Birr Castle in County Offaly in central Ireland. As shown in the drawing above, it appeared to him rather lile a spider crab. The 72 inch was the world's largest telelescope for many years. At the heart of the Crab Nebula is a neutron star, the result of the collapse of the original star's core. Although only around 20 km in diameter it weighs more than our Sun and is spinning 30 times a second. Its rotating magnetic field generate beams of light and radio waves which sweep across the sky. As a result, a radio telescope will pick up very regular pulses of radiation and the object is thus also known a Pulsar. Its pulses are monitored each day at Jodrell Bank with a 13m radio telescope.

The constellation Orion

Orion
Orion

Orion, perhaps the most beautiful of constellations, will be seen in the south at around 11 - 12 pm during January. Orion is the hunter holding up a club and shield against the charge of Taurus, the Bull up and to his right. Alpha Orionis, or Betelgeuse, is a read supergiant star varying in size between three and four hundred times that of our Sun. The result is that its brightness varies somewhat. Beta Orionis, or Rigel, is a blue supergiant which, at around 1000 light years distance is about twice as far away as Betelgeuse. It has a 7th magnitude companion. The three stars of Orion's belt lie at a distance of around 1500 light years. Just below the lower left hand star lies a strip of nebulosity against which can be seen a pillar of dust in the shape of the chess-board knight. It is thus called the Horsehead Nebula. It shows up very well photographically but is exceedingly difficult to see visually - even with relativly large telescope.

The Orion Nebula
The Horsehead Nebula: Anglo Australian Observatory

Beneath the central star of the belt lies Orion's sword containing one of the most beautiful sights in the heavens - The Orion Nebula. It is a region of star formation and the reddish colour seen in photographs comes from Hydrogen excited by ultraviolet emitted from the very hot young stars that make up the Trapesium which is at its heart. The nebula, cradling the trapesium stars, is a beautiful sight in binoculars or, better still, a telescope. To the eye it appears greenish, not red, as the eye is much more sensitive to the green light emitted by ionized oxygen than the reddish glow from the hydrogen atoms.

The Orion Nebula
The Orion Nebula: David Malin