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The Night Sky December 2012

Compiled by Ian Morison


A great month to view Jupiter and the Geminid meteor shower.


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

The Hubble Image of the Tadpole Galaxy

Hubble, NASA, ESA; processed by Bill Snyder (Heavens MirrorObservatory).

This image by the Hubble Space telescope is of the Tadpole Galaxy, ARP 188 which lies 420 million light years away in the constellation of Draco.   Its tail is about 280 thousand light years long and was formed by tidal forces from a passing galaxy.   This galaxy is now some 300 thousand light years behind ARP 188 and is visible behind the galaxy's spiral arms in the upper right.   In the future, the stars, dust and gas within the tail will form daughter galaxies orbiting Arp 188.


Highlights of the Month

December - a great month to view Jupiter!

Jupiter
Jupiter imaged by Damian Peach

This is the second of three great months to observe Jupiter.   It now lies in Taurus and so is high in the ecliptic and hence, when due south, at an elevation of ~60 degrees.   It is looking somewhat different than in the last few years as the north equatorial belt has become quite broad.   The Great Red Spot is currently a pale shade of pink but can be easily seen as a large feature in the South Equatorial Belt.   An imaging opportunity occurs this month when a complete rotation can be observed at an elevation of greater than 20 degrees and against a dark sky.   Jupiter is at opposition on the 3rd of December so will then cross the meridian around midnight.

The features seen in the Jovian atmosphere have been changing quite significantly over the last few years - for a while the South Equatorial Belt vanished completely but has now returned to its normal wide state.   The diagram on right shows the main Jovian features as imaged by the author at the beginning of December 2012.

The image by Damian Peach was taken with a 14 inch telescope in Barbados where the seeing can be particularly good.   This image won the "Astronomy Photographer of the Year" competition in 2011.

See more of Damian Peach's images: Damian Peaches Website"





Jovian Features
Features in Jupiter's atmosphere - December 2013.



December: Look for the Great Red Spot on Jupiter

Great Red Spot
Observe the Great Red Spot
Image: NASA

This list gives some of the best evening times during December to observe the Great Red Spot which should then lie on the central meridian of the planet.

1st   19:47         20th 20:24

3rd   21:34         22nd 22:02

5th   23:03         24th 23:40

8th   20:32         27th 21:10

13th 19:39         29th 22:48

15th 21:17         31st 22:48

17th 22:55


December 1st - 1 hr before Dawn: Saturn, Venus and Mercury.

Saturn
Dec 21st: Saturn, Venus and Mercury
Image: Stellarium/IM

This month, Saturn, in the constellation Virgo, is visible in the pre-dawn sky and will make a nice grouping with Venus and Mercury, all three lying below the star Spica.


December 3rd 22:45 to 02:00: The Moon occults the open cluster M67

The Moon occults M67
The Moon Occults M67
Image: Stellarium/IM

Around midnight on the 3rd/4th of December, the Moon passes in front of the open cluster M67 in the constellation of Cancer.   From about 22:45 the Moon's western (bright) limb will begin to occult the stars.   The first stars to be occulted will begin to reappear beyond the dark limb at around 01:00.   As the Moon is not that far away, parallax effects mean that the precise times will depend on your location.

December 10/11th - 1 hr before Dawn: Saturn, Venus and Mercury and a thin waning crescent Moon

Saturn
Dec 21st: Saturn, Spica and a thin crescent Moon
Image: Stellarium/IM

On the 10 and 11th, Saturn, Venus and Mercury in the constellation Virgo, are visible in the pre-dawn sky and joined by a thin waning crescent Moon.


December 14th and 15th after midnight: the Geminid Meteor Shower.

Dec14th
Image:Stellarium/IM

The Geminids

The early mornings of December 14th and 15th will give us the chance, if clear, of observing the peak of the Geminid meteor shower.   This is a great year for observing them as these dates correspond to New Moon so there will be no moonlight to hinder our view!  An observing location well away from towns or cities will also 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.  If it is clear it will be cold - so wrap up well, wear a woolly hat and have some hot drinks with you.

December 22nd/23rd - midnight onwards : the Ursid Meteor Shower

Ursid meteor Shower
The Ursid meteor shower

The night of the 22nd/23rd December is when the Ursid meteor shower is at its best - though the peak rate of ~10-15 meteors per hour is not that great.   The waxing gibbous Moon sets at 03:00 UT, so moonlight will not obstruct our view in the hours before dawm.   The radiant lies close to the star Kochab in Ursa Minor (hence their name), so look northwards at a high elevation.   Occasionally, there can be a far higher rate so its worth having a look should it be clear.

Around the 13th December - Find M31 - The Andromeda Galaxy - and perhaps M33 in Triangulum

M31
How to find M31
Image: Stellarium/IM

In the evening, the galaxy M31 in Andromeda is visible 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.

Around new Moon (13th Dec) you may also be able to spot M33, the third largest galaxy after M31 and our own galaxy in our Local Group of galaxies.   It is a face on spiral and its surface brightness is pretty low so a dark, transparent sky will be needed to spot it using binoculars (8x40 or, preferably, 10x50).   Follow the two stars back from M31 and continue in the same direction sweeping slowly as you go.   It looks like a piece of tissue paper stuck on the sky just a bit brighter than the sky background.   Good Hunting!


December 10-15th: Search for Neptune - with no Moon in the sky.

Neptune
Neptune near closest approach
Image: Stellarium/IM

Neptune, with a magnitude of 7.8 should be easily seen in binoculars under a dark, early evening, sky.   It will be due south around 18:30 in the evening.   Neptune lies about 2 degrees above the star Iota Aquarii as shown on the chart.   Iota Aquarii can be found by moving 5 degrees to the left and slightly upwards from the star Delta Capricorni.


Christmas Day after sunset: Jupiter and a full Moon

Jupiter and the Moon
Jupiter and a nearly Full Moon
Image: Stellarium/IM

If its clear after sunset on Christmas Day, Jupiter will be seen to lie very close to the Moon 3 days before full.  If you are lucky, you may also spot Father Christmas on his way back to the North Pole (actually Lapland).

The author imaged Jupiter close to a full Moon in November 2012 using a 102 mm Takahashi refractor and Imaging Source webcam; analysing 11,000 avi frames (in Registax V6) and compositing segments of the lunar surface in Microsoft ICE to give the full lunar image.   To fit within a reasonably sized frame, Jupiter had to be placed closer to the Moon in the image than was actually the case.

Moon and Jupiter
Jupiter and the Full Moon, November 2012.
Image: Ian Morison




December: 4/5th and 20/21st: The Alpine Valley

Alpine Valley
Alpine Valley region

An interesting valley on the Moon: The Alpine Valley
These are good nights to observe an interesting feature on the Moon if you have a small telescope.  Close to the limb is the Appenine mountain chain that marks the edge of Mare Imbrium.  Towards the upper end you should see the cleft across them called the Alpine valley.   It is about 7 miles wide and 79 miles long.   As shown in the image a thin rill runs along its length which is quite a challenge to observe.  Over the next two nights following the 3rd/4th the dark crater Plato and the young crater Copernicus will come into view.   This is a very interesting region of the Moon!

The Alpine Valley
The Alpine valley and the crater Plato





M 109 imaged with the Faulkes Telescope

Messier 109
Messier galaxy M 109
Image: Danial Duggan
Faulkes Telescope North.

Spiral galaxy M109, imaged by Daniel Duggan.
This image was taken using the Faulkes Telescope North by Daniel Duggan - for some time a member of the Faulkes telescope team.   M 109 is a Barred Spiral some 83 million light years away that lies is a loose collection of Galaxies called the Ursa Major Cloud that may contain over 50 galaxies.

Learn more about the Faulkes Telescopes and how schools can use them: Faulkes Telescope"











Learn more about the Faulkes Telescopes and how schools can use them: Faulkes Telescope"











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 13th December 20th December 28th December 6th

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.

Plato and the Alpine valley
Plato and the Alpine Valley.

Please follow the link to the Lunar World Record 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.



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 rises around sunset at the beginning of December reaching opposition around midnight so will be visible all night.   When due south it will lie some 60 degrees above the horizon in the constellation of Taurus, the Bull.   Shining at magnitude -2.8 it starts December lying just ~5 degrees to the upper left of the star Aldebaran, the eye of the Bull.   Jupiter is moving westwards in the sky in retrograde motion and will do so until the beginning of February 2013, so whilst its magnitude stays at -2.8 it will end the month slightly up to the right of Aldebaran as it moves above the Hyades Cluster in the direction of thr Pleaides Cluster.   During the month its angular diameter drops slightly from 48.4 to 47.5 arc seconds so even a small telescope will show plenty of detail with the bright zones and darker bands crossing the disk and up to four Gallilean moons visible.


See highlights above.

Saturn

Saturn
The planet Saturn. Cassini - Nasa

Saturn rises at 4 am as December begins and by 2:30 am at month's end so will be visible well above the eastern horizon before dawn by the end of the month.  Both its magnitude and angular size increase during the month: from +0.7 to +0.6 magnitudes and from 15.7 to 16.1 arc seconds respectively.   It has lain in Virgo for three years now, but crosses into Libra in early December.   The good news is that the rings have now opened out to just over 18 degrees from the line of sight and will be at their best for 6 years!   We are now observing the southern hemisphere whilst much of the northern hemisphere will be hidden by the rings.   With a small scope one should now be able to spot Cassini's Division within the rings if the "seeing" is good, but we will have to wait a month or so for Saturn to rise higher into the pre-dawn sky for really good views.


See highlight above.

Mercury

Mercury.
Messenger image of Mercury Nasa

Mercury, reaches greatest western elongation on the 4th of December when it will separated by 21 degrees from the Sun.   Shining at magnitude -0.5 throughout the month, it then rises two hours before the Sun, not far from Venus, in what is an excellent appararition for northern hemisphere observers.   As December begins Mercury will be 48% illuminated and have an angular size or 7.4 arc seconds, whilst by month's end, its 96% illuminated disk will be 4.8 arc seconds across.


See highlight above.


Mars

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

Mars, moving eastwards in from Sagittarius into Capricornus on the 24th, is visible low in the west after sunset whilst its rapid motion through the heavens keeps it visible throughout the month.   It shines at magnitude +1.2 throughout the month whilst its angular diameter falls from 4.3 to 4.2 arc seconds so it is very unlikly that any surface markings could be seen on its salmon-pink disk.   On the 1st of the month, its elevation is will be about 8 degrees in the southwest as darkness falls one hour after sunset and this remains much the same throughout the month.



Venus

Venus
Venus showing some cloud structure

Venus. is now getting closer to the Sun but,with a magnitude close to -4 is still easily visible the pre-dawn sky though now somewhat closer to the horizon than last month.   As dawn breaks it will start the month at an elevation of ~17 degrees, but this will drop to ~10 degrees by month's end.   During the month its angular size drops from 11.6 to 10.9 arc seconds but, at the same time, the percentage illumination increases from 88 to 94% so the brightness does not change, remaining at -4.0 magnitudes.


See highlight above.

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.

Albireo
Albireo: 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 Albireo, 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