The Night Sky July 2012
Compiled by Ian Morison
An occultation of Jupiter and its Moons
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 2012 Venus Transit
Hinode Spacecraft NAOJ,JAXA,NASAThis wonderful image shows Venus as its disk almost fully falls over the Sun's surface between 1st and 2nd contact on June 6th. The thin rim of light seen around the limb is sunlight refracted around the surface by Venus' thick atmosphere. It was sad that cloud prevented the final stages of the transit being seen in the UK. Hinode, formerly Solar-B, is a Japanese spacecraft with collaboration from the USA and UK. The image was taken with a 0.5 m Gregorian optical telescope having a resolution of 0.2 arc seconds over a field of view of 400 x 400 arc seconds. (Venus had an angular diameter of 58 arc seconds during the transit - about 1/30th of the Sun's diameter) I find it interesting that with solar glasses (seen from New Zealand) Venus appeared as a very clear circular disk against the Sun's surface. As the Eye's resolution is only about 30 arc seconds, theoretically one should not be able to see a distinct disk - but we can. I suspect that this is similar to the fact that we see a very sharp edge to the Moon but it really should be a little blurred. I think these observations show that our brain does quite a bit of work on the images captured by our retina!
Highlights of the Month
Early July: Observe Noctilucent Clouds
The first half of July is still a good month for observing Noctilucent clouds high (about 80 km altitude) in the Earth's atmosphere. They appear as bright, whitish-blue whisps above the north, north-western and north-eastern horizons and are most obvious after midnight. They are illuminated by the Sun which is, this month, not far below the horizon towards the north. They appear to be more prominent than in the past (and were not observed until the mid-19th century) and may be associated with the fact that there is now more methane in the atmosphere. This can dissociate into water vapour in the high atmosphere allowing ice clouds to form where, otherwise, it would be too dry. If you do observe them, noting the time and elevation at which they are seen, please submit your observations to Tom McEwan's NLC site: www.nlcnet.co.uk/.
July 1st -10th: Venus and Jupiter in the pre-dawn sky
During the first week of so of July, Venus lies in the Hyades Cluster close to the star Aldebaran and may be seen with Jupiter and the Pleiades Cluster above in the pre-dawn sky. On the 7th, it is just 1 degree away from Aldebaran - this should make a very nice photographic skyscape!
July 15th before dawn: An occultation of Jupiter by the Moon seen from the south-east of the UK.
Before dawn on the morning of the 15th July, we have a chance of seeing Jupiter very close to a crescent Moon, both lying above the Hyades cluster with the bright (interloper) star Aldebaran and with the planet Venus further below. This would make a lovely photo opportunity! However, if you live in the south-east of the UK Jupiter will be fully occulted! Here, from 02:48 BST, first the satellites Europa and Io will disappear followed closely by Jupiter itself. Over a period of ~3 minutes Jupiter will be covered and finally the satellites Ganymede (at ~02:58) and Callisto. Not long afterwards at ~03:06, Io reappears with Jupiter following on behind at ~03:09. As it is avery shallow occultation, the times will vary dependent on your location within the occultation zone. Further to the north-west one will see a grazing occultation when part of Jupiter's disk is covered whilst, for most of the country we will just see Jupiter pass close by - still a great sight!
July 30th: Saturn and Mars after sunset
As Mars moves eastwards across the sky, it is approaching Saturn and the last evening of the month sees them just 8 degrees apart. In the middle of next month we will see Mars glide between Saturn and Spica.
July 28th: Two Great Lunar Craters
Two great Lunar Craters: Tycho and Copernicus
This is a great night to observe two of the greatest craters on the Moon, Tycho and Copernicus, as the terminator is nearby. Tycho is towards the bottom of Moon in a densely cratered area called the Southern Lunar Highlands. It is a relatively young crater which is about 108 million years old. It is interesting in that it is thought to have been formed by the impact of one of the remnents of an asteroid that gave rise to the asteroid Baptistina. Another asteroid originating from the same breakup may well have caused the Chicxulub crater 65 million years ago. It has a diameter of 85 km and is nearly 5 km deep. At full Moon - seen in the image below - the rays of material that were ejected when it was formed can be see arcing across the surface. Copernicus is about 800 million years old and lies in the eastern Oceanus Procellarum beyond the end of the Apennine Mountains. It is 93 km wide and nearly 4 km deep and is a clasic "terraced" crater. Both can be seen with binoculars.
A Messier Object imaged with the Faulkes Telescope: Messier 16 - The Eagle Nebula
The Eagle Nebula, M16, imaged by Nik Szymanek.
This image was taken using the Faulkes Telescope North by Nik Szymanek - one of the UK's leading astro-photograpers. M16 is also called the Eagle Nebula due to its resemblence to an eagle - it even has a fish in its tallons! It lies about 7000 light years from the Earth in the constellation Serpens. It is a star formation region with the pinky-red colour due to hydrogen excited by the ultraviolet light from the young stars in the nebula. The stars ages range from ~1 to ~5.5 million years old. The longest of the pillars is about 7 light years in length - it is in these pillars of dust that new stars are forming.
Learn more about the Faulkes Telescopes and how schools can use them: Faulkes Telescope"
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 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|
|July 19th||July 26th||July 3rd||July 11th|
Some Lunar Images by Ian Morison, Jodrell Bank Observatory: Lunar Images
A World Record Lunar Image
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 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.
Jupiter is now be visible in the pre-dawn sky rising a couple of hours before the Sun at the beginning of the month. On July 1st it lies between the Hyades and Pleiades in Taurus and is just a few degrees away from Venus. They will be then be seen low in the east-northeast. Shining at magnitude -2.1 during the month, its angular diameter increases slightly from 34.2 to 35.5 arc seconds.
See highlights above.
Saturn, like Mars, is now nearing the end of its apparition and, as July begins, is seen low in the west after sunset shining at magnitude +0.7. It the lies in Virgo just 5 degrees north of the first magnitude star Spica, Alpha Virginis. Its disk is ~17 arc seconds across and the rings are ~13.5 degrees from the line of sight. On July 15th it is at "quadrature" (90 degrees east of the Sun). This helps it appear three dimensional and nicely shows the planet's shadow on the ring system. So its still worth having a look!
Mercury, can be seen shortly after sunset during the first few days of the month and reaches greatest elongation (when its angular separation from the Sun is greatest) on July 1st. However, its elevation in the west-northwest is only ~5 degrees so it will not be easily seen and binoculars will almost certainly be needed - but wait until the Sun has set!It passes between the Earth and the Sun on 28th of July (called inferior conjunction) and will reappear in the predawn sky next month.
Mars, moving eastwards through Virgo is now, sadly, well past its best. Moving further away from us, its magnitude fades from +0.9 to to +1 during the month as it is seen low in the sky just south of west. On the 1st of the month, its elevation is only ~17 degrees as darkness falls and this has reduced to just 6 degrees by the end of the month. At the same time its angular diameter shrinks from 6.5 arc seconds down to 5.9 seconds so it is unlikely that a small telescope will enable you to see any surface markings.
See highlight above.
Venus. has reappeared into the pre-dawn sky and rises about an hour before sunrise. It shows a crescent phase as shown in the highlights above. It lies within the "V" shaped Hyades cluster close to the star Aldebaran in Taurus. During the month its angular size drops from 42 to 31 arc seconds but, at the same time, the percentage of its disk that is illuminated increases and the interesting effect is that the brightness (at around -4.5) remains pretty constant.
See highlights above.
Find more planetary images and details about the Solar System: The Solar System
The late evening July Sky
This map shows the constellations seen towards the south at about 10pm BST in mid July. The most prominent star, just a little west of South, is Arcturus in Bootes. It is the second (after Sirius) brightest star in the northern sky. High overhead towards the north (not shown on the chart) and up to the right of Arcturus lies Ursa Major with its prominent grouping of the Plough. As one moves southwards to the left of Bootes one first crosses the constellation Hercules with its magnificent globular cluster, M13, and then across the large but not prominent constellation Ophiucus until, low above the southern horizon lie Sagittarius and Scorpius. Those in the south of the UK - and even better in Southern Europe - will spot the bright red star Antares. Rising in the east 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".
The constellation Ursa Major
The stars of the Plough, shown linked by the thicker lines in the chart above, form one of the most recognised star patterns in the sky. Also called the Big Dipper, after the soup ladles used by farmer's wives in America to serve soup to the farm workers at lunchtime, it forms part of the Great Bear constellation - not quite so easy to make out! The stars Merak and Dubhe form the pointers which will lead you to the Pole Star, and hence find North. The stars Alcor and Mizar form a naked eye double which repays observation in a small telescope as Mizar is then shown to be an easily resolved double star. A fainter reddish star forms a triangle with Alcor and Mizar.
Ursa Major contains many interesting "deep sky" objects. The brightest, listed in Messier's Catalogue, are shown on the chart, but there are many fainter galaxies in the region too. In the upper right of the constellation are a pair of interacting galaxies M81 and M82 shown in the image below. M82 is undergoing a major burst of star formation and hence called a "starburst galaxy". They can be seen together using a low power eyepiece on a small telescope.
Another, and very beautiful, galaxy is M101 which looks rather like a pinwheel firework, hence its other name the Pinwheel Galaxy. It was discovered in1781 and was a late entry to Messier's calalogue of nebulous objects. It is a type Sc spiral galaxy seen face on which is at a distance of about 24 million light years. Type Sc galaxies have a relativly small nucleus and open spiral arms. With an overall diameter of 170,000 light it is one of the largest spirals known (the Milky Way has a diameter of ~ 130,000 light years).
Though just outside the constellation boundary, M51 lies close to Alkaid, the leftmost star of the Plough. Also called the Whirlpool Galaxy it is being deformed by the passage of the smaller galaxy on the left. This is now gravitationally captured by M51 and the two will eventually merge. M51 lies at a distance of about 37 million light years and was the first galaxy in which spiral arms were seen. It was discovered by Charles Messier in 1773 and the spiral structure was observed by Lord Rosse in 1845 using the 72" reflector at Birr Castle in Ireland - for many years the largest telescope in the world.
Lying close to Merak is the planetary nebula M97 which is usually called the Owl Nebula due to its resemblance to an owl's face with two large eyes. It was first called this by Lord Rosse who drew it in 1848 - as shown in the image below right. Planetary nebulae ar the remnants of stars similar in size to our Sun. When all possible nuclear fusion processes are complete, the central core collpses down into a "white dwarf" star and the the outer parts of the star are blown off to form the surrounding nebula.
The constellation Hercules
Between the constellation Bootes and the bright star Vega in Lyra lies the constellation Hercules.The Red Giant star Alpha Herculis or Ras Algethi, its arabic name, is one of the largest stars known, with a diameter of around 500 times that of our Sun. In common with most giant stars it varies its size, changing in brightness as it does so from 3rd to 4th magnitude. Lying along one side of the "keystone" lies one of the wonders of the skies, the great globular cluster, M13. Just visible to the unaided eye on a dark clear night, it is easily seen through binoculars as a small ball of cotten wool about 1/3 the diameter of the full Moon. The brightness increases towards the centre where the concentration of stars is greatest. It is a most beautiful sight in a small telescope. It contains around 300,000 stars in a region of space 100 light years across, and is the brightest globular cluster that can be seen in the northern hemisphere.
The constellation Virgo
Virgo, in the south-east after sunset this month, is not one of the most prominent constellations, containing only one bright star, Spica, but is one of the largest and is very rewarding for those with "rich field" telescopes capable of seeing the many galaxies that lie within its boundaries. Spica is, in fact, an exceedingly close double star with the two B type stars orbiting each other every 4 days. Their total luminosity is 2000 times that of our Sun. In the upper right hand quadrant of Virgo lies the centre of the Virgo Cluster of galaxies. There are 13 galaxies in the Messier catalogue in this region, all of which can be seen with a small telescope. The brightest is the giant elliptical galaxy, M87, with a jet extending from its centre where there is almost certainly a massive black hole into which dust and gas are falling. This releases great amounts of energy which powers particles to reach speeds close to the speed of light forming the jet we see. M87 is also called VIRGO A as it is a very strong radio source.
Below Porrima and to the right of Spica lies M104, an 8th magnitude spiral galaxy about 30 million light years away from us. Its spiral arms are edge on to us so in a small telescope it appears as an elliptical galaxy. It is also known as the Sombrero Galaxy as it looks like a wide brimmed hat in long exposure photographs.
The constellations Lyra and Cygnus
This month the constellations Lyra and Cygnus are rising in the East 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 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!
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!
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.
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.
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.
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!
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.
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.