The Night Sky September 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
The VLT observing the Galactic Centre using an artificial star.
Image: Yuri Beletsky. ESO.
Two of the VLT telescopes in Chile operated by the European Southern Observatory. One is observing the Galactic Centre using the technique of Adptive Optics. This analyses the image of a point source (such as a bright star) to solve for the effects of the atmosphere which is distorting the image. But the star has to be very close to the object to be imaged for this to work well and there may well not be a bright star close enough. In this case an "artificial star" is made by exciting sodium atoms in the upper atmosphere with a laser beam tuned to the Sodium D lines (hence its orange colour). Once the effect of the atmosphere has been found, a deformable mirror in the light path within the telescope is rapidly adjusted to make appropriate corrections. It is particluarly suitable for infrared observations and this has, for example, allowed the VLT to image three planets orbiting a star.
In the sky, Alpha and Beta Centauri are just to the left (at the top) of the right hand telescope. These point down to the Southern Cross just below a very dark cloud called the Coal Sack. Above the left hand telescope is seen the Small Magellanic Cloud above which is the globular cluster 47 Tucanae.
Highlights of the Month
Around new Moon ~18th September: Find Uranus and spot the asteroid Juno
Chart showing position of Uranus
Image: Stellarium/IM
Uranus is at opposition on September 17th and will have a magnitude of +5.7 lying just below the circlet of Pisces which itself lies below the square of Pegasus. The chart show its position mid month as it moves down and to the right towards the star Beta Aquari. Under very dark skies it would just be visible to the unaided eye, but binoculars will probably be need to see it from our light polluted skies. On the 17th also, the asteroid Juno passes just 4 degrees to lower left of Uranus as shown on the second chart. Follow past two 5th to 6th magnitide stars to a pair of similar brightness stars roughly at rightangles. Juno will be passing to their left. The only way to be sure that you have seen it is to draw or photograph the positions of the objects in the region on two or more nights and see which moves!
Chart showing the position of Juno
Image: Stellarium/IM
August 2nd/3rd - North America: Jupiter without any moons!
Jupiter with no moons!
Image: Stellarium/IM
At the beginning of last month you could observe Jupiter with apparently 5, not 4, moons! This was because Jupiter passed in front of the +5.9 magnitude star 45 Capricorni, which is only just fainter than Callisto. On the night of the 2nd/3rd of September between 04:45 and 06:29 UT, sadly after Jupiter has set as seen from the UK, Jupiter will appear to have lost all its moons. Ganymede and Europa will lie in front of Jupiter, Io will be behind, and Callisto will be in Jupiter's shadow. This is the last time that Jupiter will appear moonless until 2019.
Find M31 - The Andromeda Galaxy
How to find M31
Image: Stellarium/IM
In the late evening, the galaxy M31 in Andromeda is visible in the south-east. 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 resonably 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. Good Hunting!
Late evening 12th September: A crescent moon passes M35
Moon and M35 at 23:00 UT on the 12th September.
Image: Stellarium/IM
Late evening in the 12th of September, the Moon passes just 0.5 degrees to the left of the open cluster in Gemini, M35. As both the Moon and the cluster have apparent angular sizes of ~0.5 degrees it means that the Moon will just skim past the edge of the cluster. They will be best seen with binoculars or a small telescope as the glare of the moon will prevent you seeing the cluster stars with your unaided eye. This would be an interesting, but tricky, scene to photograph due to the imbalance in brightness between the Moon and cluster. [NB: In the simulated image the glare of the Moon has been removed!]
September: A good month to spot Neptune
Chart to help find Neptune
Image Stellarium/IM
Neptune passed opposition (and hence due south around midnight UT) last month and so will be seen in Capricornus towards the south in the late evening during September. It lies just over 2 degrees above the +2.8 magnitude star Delta Capricorni - so will be easily spotted using binoculars at magnitude +7.8 towards the top of the field of view if the star is placed in the lower centre of the field. First find Jupiter - the brightest object in the south - and sweep with binoculars 4 (1st Sept) to 6 (31st Sept) degrees to the east to pick up the two stars Delta (left at +2.9) and Gamma (right at +3.7) Capricorni. Neptune lies above and a touch to the right of Delta Capricorni. A reasonably sized telescope will show Neptune as a tiny, bluish coloured, disk
Observe 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
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 |
|---|---|---|---|
| September 18th | September 26th | September 4th | September 12th |
Some Lunar Images by Ian Morison, Jodrell Bank Observatory: Lunar Images
A 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.
The Lunar World Record 2009: Lunar World Record
The Planets
A montage of the Solar System. JPL / Nasa
Jupiter
A Cassini image of Jupiter . Nasa
Jupiter, now lying in Capricornus, is easily visible in the evening sky and is seen in the south-east after twilight. During September, its magnitude drops very slightly; from -2.8 to -2.7. It has an angular size of 48 arc seconds at the beginning of the month so a small telescope will show much detail on the surface if seeing conditions are good. Sadly at the present time Jupiter is close to the lowest part of the ecliptic and never reaches more than ~25 degrees above the horizon even when it will be seen due south, so highest in the sky. On the 29th, Jupiter will lie around 2 degrees below a 82% illuminated waxing crescent Moon. 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 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 sufficint light.
Saturn
The planet Saturn. Cassini - Nasa
Saturn ,sadly, has virtually become lost in the Suns glare and will not be seen again for a month or so when it reappears in the pre dawn sky. This is a pity as, on September 4th, its rings a edge on to the Sun and so are not illuminated and thus dissapear. It is just possible that on the 4th, given a very low western horizon, you might just be able to spot it 2 degrees above the horizon at 8pm BST. Do not search for it with binoculars or a telescope until after the Sun has set!
Mercury
Messinger image of Mercury Nasa
Mercury: passes behind the Sun (called inferior conjunction) on the 20th September so it will not be visible until the very end of the month in the dawn sky - and then with difficulty. Perhaps the best chance of spotting it is on the 30th when, just after 06:00 BST and at magnitude +0.8, it will lie 10 degrees below the planet Venus. You need a very low eastern horizon to have a chance of seeing it though!
Mars
A Hubble Space Telescope image of Mars.
Jim Bell et al. AURA / STScI / Nasa
Mars is becoming more prominent in the morning sky rising at about midnight BST during the month. It lies in the constellation Gemini and is close to the open cluster M35 at the beginning of the month. Its magnitude increases slowly from +1 to +0.8 whilst its angular size increases from 5.8 to 6.6. arc seconds. Under ideal seeing conditions, a telescope might begin to show some of the more prominent features such as Syrtis Major. On the 25th it will lie about 1 degree above the +3.5 magnitude star Delta Geminorum. We will have to wait a month or so until it will be seen more easily as the nights get longer and it rises earlier in the night! The Earth will, of course, be overtaking Mars "on the inside track" so we will come closer to it and its angular size will increase so allowing more features on the surface to be seen.
Venus
Venus showing some cloud structure
Venusis now moving towards the far side of the Sun and so getting closer in angle to it. It will thus be best seen at the beginning of September as it lies in the constellation Cancer, just below the Beehive Cluster, M4. During the month it moves down into Leo where, on the 20th, it will be just half a degree to the upper left of Leo's brightest star, Regulus. A small telescope will show a waxing gibbous disc dropping from 12.5 arc seconds in diameter to 11.3 arcseconds as it moves towards the far side of the Sun. It magnitude remains at -3.9 during the month. An interesting fact about its brightness is that it stays pretty constant at about -4 for most of the time that it is visible even though the apparent phase changes greatly. When the phase is thin, Venus is nearer to us and so the effective reflecting area of Venus as seen from Earth remains pretty constant.
Radar image showing surface features
Find more planetary images and details about the Solar System: The Solar System
The Stars
The Evening September Sky
The September Sky in the south - early Sept:~11pm, late Sept:~10pm
This map shows the constellations seen towards the south in late evening. To the south in early evening moving over to the west as the night progresses 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 constellations Lyra and Cygnus
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!
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
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
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: 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
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.
Brocchi's Cluster - The Coathanger
The constellations 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.
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 in triangulum - David Malin
