What to see in August

The Night Sky August 2011

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
• Highlights of the Month
• The Planets
• The Stars

Image of the Month

Hubble's Cepheid variable
Peter Shah, Edwin Hubble and HST (NASA,ESA). Composite: IM.
At the lower right of this composite image is what was, perhaps, the most significant single astronomical image of the last century. Taken by Edwin Hubble in 1923 it shows the location of what he first thought was a Nova - a star that brighten's suddenly. He later found that it was, in fact, a bright variable star known as a Cepheid Variable, so he crossed out the "N" and replaced it it with "VAR". Cepheid variable are named after the prototype star of this class of variables, Delta Cepheus, which had been discovered by John Goodright in 1784. The brightness of the star that Hubble had observed was changing in brightness with a period of just over 30 days. Observing Cepheid Variables in the Small Magellanic Cloud (SMC), Henrietta Leavitt had shown that such a star was ~10,000 times brighter than our Sun. This enabled Hubble to calculate the distance to the star - and hence the Andromeda Galaxy in which it lay. He derived a distance of ~850,000 light years which showed that the galaxy was well beyond our own Milky Way galaxy that was then thought to be ~350,000 light years across. (These are well below the currently accepted values partly due to the fact that there are two types of Cepheid Variables, and those observed by Hubble in the Andromeda Galaxy were several times brighter than those observed by Henrietta Leavitt in the SMC.) Hubble's observations of Cepheid Variables in more distant galaxies and hence his calculation of their distances coupled with velocity measurements made by Vesto Slipher led to his discovery that the Universe was expanding.
The upper right HST image shows the stars position and the wonderful image made by Peter Shah shows the positions of the two images within the galaxy.

Highlights of the Month

August 11th to 14th: View the Perseid Meteor Shower- in spite of the Moon.

A Perseid Meteor
Image: S. Kohle and B. Koch, Astronomy Institute, Bonn University.

If it is clear on the early mornings of the 11th to 14th of August, one has a chance of seeing the meteors in the Perseid Meteor Shower - the year's most dependable meteor shower. However, this year, the peak of the shower on the morning of the 13th coincides with the full Moon! This will make it difficult to see the fainter meteors, but the brighter ones will still be visible. Look up towards the North-East from 11 pm onwards on the nights of August 11th, 12th and 13th and 14th. The peak of activity - when you might expect to see 20-30 meters an hour is predicted to be between 00:30 and 03:00 BST on the morning of the 13th. This is the best time to observe on the other nights too as Perseus is rising in the sky and the Earth is facing the meteor stream. Most meteors are seen when looking about 50 degrees away from the "radiant" (the point from which the meteors appear to radiate from) which lies between Perseus and Cassiopea. (See the star chart below) The Perseid meteors are particles, usually smaller than a grain of sand, released as the comet Swift-Tuttle passes the Sun.
The shower in quite long lived, so it is worth looking out any night from the 10th to the 15th of August. The Moon sets at ~ 4 am on the 11th giving half an hour or so to observe before dawn. The number of possible meteors that it might be possible to see will be less than on the 13th but the Moon will not then interfere. Good hunting!

Looking East after midnight on 11th August
Image: Stellarium/Ian Morison

August around 10pm: Spot Brochi's Cluster and the double star Albireo in Cygnus.

Brochi's Cluster - The Coathanger and Albireo
Image: Stellarium/IM

By about 10 pm during the month, the constellations Cygnus, Lyra and Aquila will have risen well up into the south-east. Their three brightest stars Deneb, Vega and Altair respectivly make up the "Summer Triangle". If you sweep with binoculars one third of the way from Altair towards Vega, you should spot Brocchi's Cluster usually called "The Coathanger" as this is exactly what it looks like - but seen upside down. Its not thought to be a real cluster but an "asterism" which is a chance grouping of stars. Not far to the upper left of Brochi's cluster is, perhaps, the most beautiful double star to observe in a small telescope. It is the star Albireo which forms the head of the swan. At magnitude 3 it is the least brightest of the stars that make up a part of Cygnus called the "Northern Cross". However, when seen through a small telescope, it is seen to be made up of two stars showing a beautiful colour contrast. The brighter 3.1 magnitude component (which is itself a double star) is amber in colour whilst the 5.1 magnitude companion star is blue-green in colour. With a separation of 35 arc seconds the pair can be easily split even under poor seeing conditions - in contrast to Porrima above.

Late evening 2nd August: Comet Garrard just above M15

Comet Garrard just above the Globular Cluster M15
Image: Stellarium/IM

Comet Garrard passes from Pegasus, through Delphinus and Sagitta during the month. On the 2nd of August it passes just half a degree above the globular cluster M15 (at magnitude +6.2) in Pegasus. With a magnitude of ~+8 it will be easily visible in binoculars. On the morning of the 27th, it lies just 7 arc minutes of another globular cluster, 8th magnitude M71.

End August, late evening: Search for Neptune

Neptune at closest approach
Image: Stellarium/IM

This month, Neptune reaches opposition on August 22nd and so, with a magnitude of 7.8 it should be easily seen in binoculars under a dark sky. Around the 22nd, Neptune lies 1.6 degrees above the star Iota Aquarii as shown on the chart. Neptune is now very close to its discovery position in 1846 and has thus completed almost one complete orbit since then.

August 5th and 31st: Spot Vesta - brightest of the asteroids.

Vesta passes through Capricornus
Image: Stellarium/IM

Vesta, though not the largest asteroid or minor planet - that is Ceres, now classed as a "Dwarf Planet" - is the brightest and this month reaches a magnitude of 5.6, so it could just be seen with the unaided eye given a dark, transparent, sky. On August 5th, when it is at peak brightness, it passes close to a pair of fainter stars, whilst on the 31st it is just 20 arc seconds away from the 4th magnitude star Psi Capricorni. Vesta is due south around midnight and binoculars will easily pick it out, so why not have a try?

Vesta's position on the 5/6th August.

August 2nd and 18th: The Straight Wall

Location of the Straight Wall: IM.

The Straight Wall
The Straight Wall is best observed either 1 or 2 days after First Quarter (7th August: evening best) or a day or so before Third Quarter (evening of the 20th or 21st August best). To honest, it is not really a wall but a gentle scarp - as Sir Patrick has said "Neither is it a wall nor is it straight!".

The Straight Wall at Sunrise and Sunset.

A Messier Object imaged with the Faulkes Telescope: M1, The Crab Nebula

NGC1365
Image:Nik Szymanik
Faulkes Telescope.

Galaxy NGC 1365, imaged by Nik Szymanek.
This image was taken using the Faulkes Telescope by Nik Szymanek - one of the UK's leading astro-photograpers. NGC1365 is also known as the Great Barred Spiral Galaxy and lies at a distance of 56 million light years. It is one of the most perfect barred spirals with a straight bar and two very prominent spiral arms. Closer to the centre there is also a second spiral structure. The galaxy is an excellent "laboratory" for astronomers to study how galaxies form and evolve.
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

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
August 29th	August 6th	August 13th	August 21st

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.

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. JPL / Nasa

Jupiter

A Cassini image of Jupiter . Nasa

Jupiter is now high in the pre-dawn sky having risen at midnight at the beginning of August. It elevation at dawn is the ~50 degrees. Its magnitude is -2.5 and its angular size will slowly increase to ~44 arc seconds by month's end. It is now well worth observing (if you do not mind getting up early!) and a small telescope will easily show the equatorial bands and the Galilean moons. In contrast to Saturn which is moving towards the lower part of the ecliptic (and hence will not reach as high an elevation when due south), Jupiter, now in Aries, is moving towards the higher part of the ecliptic and so, in the next few years, will be a superb object to observe.

Saturn

The planet Saturn. Cassini - Nasa

Saturn. At the beginning of August, Saturn is still just visible low (at an elevation of ~20 degrees) in the Southwest an hour after after sunset, but by month's end it will be barely visible, at just 5 degreees elevation above the horizon, as darkness falls. It has a magnitude of +0.9 throughout the month. Compared to early last year, its apparent brightness has now increased as the rings have opened out again - now tilted at +8 degrees from edge on. The plus sign indicates that we are seeing Saturn's north pole. The rings span an angular size of ~34 arc seconds - over double the 16 arc seconds of the planet's disk. Given a small telescope it may just be be possible (given the low altitude) to see Cassini's division - a dark band that separates the A and B rings. It will also show Saturn's brightest moon, Titan, (at magnitude +8) and, given good conditions, other moons as well.

Mercury

Messenger image of Mercury Nasa

Mercury passes between the Earth and the Sun (inferior conjunction) on the 16th August and will emerge into the pre-dawn sky towards the end of the month. At around 6 am on the 27th it will have an elevation of ~7 degrees lying down to the lower left of a waning Moon and, further distant, the planet Mars.

Mars

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

Mars, shining at magnitude +1.4 in the western half of Gemini at the beginning of August, has risen to an elevation of ~30 degrees at sunrise so can be easily seen in the pre-dawn sky just north of East. By month's end Mars, now in mid Gemini, rises at 2 am and will have an elevation of 40 degrees by sunrise. Its angular size is just 4.5 arc seconds mid month and so one is unlikely to see any detail on its salmon-pink disk. On the 5th of August it passes to the lower right of the open cluster M35 which should make a nice telescopic view.

Venus

Venus showing some cloud structure

Venus passes behind the Sun on the 15th of August - called superior conjunction - and so will not be visible for a month or so when it will reappear in the evening twilight sky.

Radar image showing surface features

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

The Stars

The mid evening August Sky

The August Sky in the south - mid evening.

Now that the evenings are drawing in, the night sky gets darker earlier so encouraging one to go out to observe.
This map shows the constellations seen towards the south at about 10pm BST in mid August. High over head towards the north (not shown on the chart) lies Ursa Major. As one moves southwards 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 souther horizon lie Sagittarius and Scorpio. To the right of Hercules lie the arc of stars making up Corona Borealis and then Bootes with its bright star Arcturus. Rising in the east is the beautiful region of the Milky Way containing both Cygnus and Lyra. Below is the constellation of Aquilla, the Eagle. The three bright stars Deneb (in Cygnus), Vega (in Lyra) and Altair (in Aquila) make up the "Summer Triangle".

The constellation Ursa Major

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.

M81 and M82

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).

M101 - The Ursa Major Pinwheel Galaxy

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.

M51 - The Whirlpool Galaxy

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.

M97 - The Owl Planetary Nebula Lord Rosse's 1848 drawing of the Owl Nebula

The constellation Hercules

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 Globular Cluster M13 in Hercules. Image by Yuugi Kitahara

The constellation Virgo

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.

The Giant Elliptical Galaxy M87 HST image showing the jet

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.

M104 - The Sombrero Galaxy

The constellations Lyra and Cygnus

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

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.
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.

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 Here is the original version of this data.