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The Night Sky December 2007

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

M45 region

The region around the Pleiades star cluster
Image: copyright Tony Hallas

It is a priviledge to be able to reproduce an image made by Tony Hallas who, together with his wife Daphne, has produced some of the most beautiful astrophotos of recent years. This wide angle view of the region around the Pleades cluster in Taurus shows the blue nebulosity caused by light scattered by a dust cloud through which the cluster is passing. The nebulosity close to the cluster, seen mid-right, has been imaged many times, but the nebulosity in the left half of the 3 degree field has been rarely photographed. At the Pleiades distance of ~ 400 light years this region spans over 20 light years across. The colour of the nebulosity is blue partly as the hot young stars in the region emit much blue light and partly by the fact that due to the size of the particles they scatter blue light preferentially to red light. (This is similar to the reason that our skies are blue and the Sun at sunset appears red.) You will notice that the nebulosity shows linear striations which it implies that the dust particles that scatter the light must be alligned. This tells us two things: first that the dust particles must have some iron content - so making them tiny magnets, and secondly there must be a magnetic field for them to align along. Its amazing what a photograph can tell us!

More wonderful astronomical images by Tony and Daphne Hallas: Astro Images

Highlights of the Month

December: the Comet 17P/Holmes

Comet Holms
Comet Holmes on 13th November with Meade 8" Schmidt-Newtonian and Nikon D80
Image: Ian Morison

Click on to enlarge

We still have a comet in the sky - but sadly, no longer visible to the unaided eye. However it is still a very worthwhile object to observe with binoculars. The comet, P17/Holmes, which is ~ 240 million km from the Earth underwent a major outburst in late October and, for sometime, appeared at ~ Magnitude 3 as a new star in the constellation Perseus. To locate the comet in the evening sky - the chart below is for 10pm - first find the bright star Capella low in the east. Up and to the right is the slightly dimmer star Mirphak with the comet just up and to its right. A chart is given below to help you locate it. It moves towards the star Algol during December and January. Comet Holmes orbits the Sun every 6.88 years and was discovered by Edwin Holmes in November 1892. It was closest to the Sun in May this year but never gets closer than Mar's orbit. Try to observe it soon - it may not be visible for much longer! The tail is very short and is pointing away from us as the comet is nearly on the opposite side of us from the Sun.

Perseus
Looking east at 10 pm
Image: Stellarium/im
Comet Holmes
Position of Comet Holmes in Perseus
Image: Stellarium/im

December and January: Mars at closest approach

Mars
Mars as viewed by spacecraft showing Vallis Marineris (centre) and two of the giant volcanoes (upper left).

Mars at its best for several years

On the night of December 24th Mars will be at opposition - that is it will opposite the position of the Sun in the Sky, and thus seen due south at midnight. This is also close to the time, on December 18th, when it will be closest to us and hence its disk will be at its largest. This month it will be brighter and appear larger in the sky than it will do for eight and a half years! At this opposition it will reach just under 16 arc seconds and so a small telescope will be able to detects features on the surface such as the polar caps and the dark region Syrtis Major - an excellent reason for purchasing a telescope!

However, as Mars's orbit is elliptical, the closest seperation varies from apparition to apparition. On August 27th 2003, the Earth and Mars were as close as they virtually ever get - at least for ~60,000 years, but it was nearly as close in August 13th 1766, August 18th 1845, and August 23rd in 1924. Notice that all these dates were in August. This is not a coincidence as this is when the Earth is at its furthest from the Sun. The closet of all approaches occur when the Earth is furthest from the Sun and Mars is closest to the Sun. At these closest of close approaches, the angular size of Mars reaches 25 arc seconds. This is obviously not the case this time as the Earth is closest to the Sun in the Winter. However, in contrast to 2003 when Mars was rather low in the Sky and the atmosphere hindered our view, Mars is now in Gemini, at almost the highest part of the ecliptic, so although its angular size will be smaller, our view may even be better!

Mars peaks in brightness in late December at magnitude -1.6 when it outshines teh brightest star in the northern hemisphere, Sirius, at -1.4. At the end of December it passes just north of the star cluster M35 before pasing into Taurus on the 30th December.

December 14th after midnight: look out for the Geminid Meteor Shower - and spot Mars too.

Dec14th
Image:Stellarium/IM

The Geminids

In the early morning of December 14th will give us the chance, if clear, of observing what may be the best meteor shower this year. Any time after midnight you might see as many as 120 meteors an hour under dark and transparent skies - over one a minute. The relatively slow moving meteors arise from debris released from the asteroid 3200 Phaethon. 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. It could well be worth it!

Mars

Looking towards Gemini, you cannot fail to spot an interloper which is the brightest object in that part of the sky. It is the planet Mars!

Seek out Uranus and Neptune with binoculars or a telescope.

Uranus and Neptune
This month Uranus and Neptune
Image: Stellarium/IM

Early December is still a good time to observe the planets Uranus and Neptune - perhaps for the first time - with binocular or a small telescope. &nb &nbs On December 9th, the night of new moon, Uranus, with a magnitude of 5.8, lies up and to the left of the 4th magnitude star Lambda Aquarii. (If Lamdbda Aquarii is the centre of a clock, Uranus is at 10:00) On the 9th December it lies at an angular distance of just over 3 degrees from Lambda Aquarii. During the month it drifts slowly westwards. Binoculars will easily show it and a small telescope will show a blue-green disc just under 4 arc seconds in angular diameter. Around the time of new moon (~9th December) under dark and transparent skies you even be able to see it with your unaided eyes. Neptune is somewhat lower in elevation in Aquarius just 5 degrees to the right of the star Delta Capricornus. It is at magnitude 7.9 so binoculars will be required to spot it. Do have a go!

Find the Andromeda Galaxy and observe Algol wink!

December
Early evening in December
Image: Stellarium/IM

Late autumn is still a good time to find the Andromeda galaxy. It is near the top of the chart just to the right of centre. Start at the top left star (Alpheratz) of the square of Pegasus, move round two bright stars to the left and up a bit to reach Mirach. At this point turn sharp right, move up one star and then the same distance again. A fainter star is passed and then you should see a fuzzy glow - that is the Nucleus of the Andromeda Galaxy. 10x50 binoculars on a really dark transparent night will show the disk extending out from the nucleus.

To the left of the tiny constellation Triangulum is the Star Algol in Perseus.

It is an eclipsing binary and every 2.87 days its brightness drops by more than a magnitude and then rises again. In December you can watch this happen over a period of hours around 19:52 UT on the 6th and 21:36 UT on the 26th.

Observe the International Space Station

The International Space Station
The International Space Station

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.)

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

See where the space station is now: Current Position

The Moon

Eclipsed Moon
The passage of the Moon through the Earth's shadow March 2007: Cape Newwise 200 mm telescope and Nikon D80 camera.
Ian Morison, Jodrell Bank Observatory
new first quarter full moon last quarter
Dec 9th Dec 17th Dec 24th Dec 1st

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

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 is now passing behind the Sun, so will not be visible this month - we will have to wait a few months until it appears again in the pre-dawn sky.

Saturn

Saturn
The planet Saturn. Cassini - Nasa

Saturn As December begins, Saturn lies 8 degrees down to the lower left of the star Regulus in Leo and is seen in the pre-dawn sky. It starts the month at magnitude +0.7 with an angular size of 18 arc seconds. Saturn will not be as bright this coming year as it sometimes is: the rings are closing (just ~ 8 degrees tilt to us and subtending only 5 arc seconds) and thus there is less apparent reflecting area. the rings will be seen (or rather - not seen) edge on in 2009 and it will not be until 2016 that they will be at their widest again. A small telescope will easily show its moon, Titan, and show some bands around the surface. As Saturn gradually rises earlier than the Sun and can be seen higher in the sky, it will be easier to make out its surface features.

Mercury

Mercury.
Mariner 10 composite image of Mercury. Nasa

Mercury On the 17th of November, Mercury reaches superior conjunction - which means that it is on the far side of the Sun form the Earth. As a result it will not be visible this month.

Note that the blank region in the image above is simply because this part of Mercury's surface has not yet been imaged in detail.

Mars

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

Mars, seen in the constellation Gemini this month, starts the month at magnitude magnitude -1.3 and increases as the month progresses reaching -1.5 by the end of the month. The seperation between the Earth and Mars is now decreasing as it heads towards opposition - when the Earth lies between Mars and the Sun and is closest to us. Its angular size is thus increasing and will reach nearly 16 arc seconds on the 18th December. Up to the 15th November, Mars was seen to move eastwards through the constellation Gemini but then, as the Earth passes Mars "on the inside track", Mars begas to retrace its steps and moves westwards through the constellation. This is known as retrogarde motion and will take Mars back into Taurus before, on the 2nd of February 2008, it moves eastwards again reaching Gemini on the 6th March. These next couple of months months are thus the best time to observe Mars which will be closest to Earth on the 18/19th of December.

See also the highlight above.

Venus

Venus
Venus showing some cloud structure

Venus dominates the morning sky shining with a magnitude of -4.2 during the month. It lies in the constellation Virgo. As the month progresses, the angular size drops from ~18 arc seconds to below 15 arc seconds, but the illuminated area of the surface increases. These two factors which affect its brightness roughly cancel out and the brightness hardly drops - ending the month at -4.1 magnitudes. As it is never that high above the horizon, dispersion in the atmosphere tends to colour its image and it will be seen best in a telescope when a filter is used to observe it at one colour of light such as by the use of a green filter. A narrow band filter, such as an O III filter, will give even cleaner images.

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