Monthly Night Sky Guide August 2023
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.
New(ish)
The author's: Astronomy Digest
which, over time, will provide useful and, I hope, interesting articles for all amateur astronomers. A further aim is to update and add new material to link with the books recently published by Cambridge University Press and which are described on the home page of the digest. It now includes well over 100 illustrated articles.Image of the Month
The Summer Triangle
This month Cygnus, Lyra and Aquilla lie overhead in the evenings. Their three brightest stars, Deneb, Vega and Altair make up the Summer Triangle as seen in the image. The dark dust lane called the Cygnus Rift crosses the band of the Milky Way. Below Deneb is the North America Nebula and between Altair and Vege is a lovely asterism called 'The Coathanger'. Th tiny constellation Delphinus lies below the triangle.
Highlights of the Month
The mornings of August 12th and 13th - midnight to dawn: look out for the Perseid meteor shower.
A Perseid meteor
If clear, these mornings should give us a chance of observing the Perseid meteor shower - produced by debris from the comet Swift-Tuttle. The early morning of the 12th August will give us the best chance, if clear, of viewing the shower, but the peak is quite broad and so it is well worth observing on the nights before and after. Most meteors are seen looking upwards about 50 degrees from the "radiant" which lies between Perseus and Cassipeia. Happily, this year, the Moon is New on the 16th so its light will not hinder our view! NB: As we need to view a very wide area of sky, normal binoculars would be of no use but the Vixen SG 2.1 x 42 that I have reviewed in the Astronomy Digest could be useful albeit over the smaller field of view of ~27 degrees.
Looking East at ~1am on the morning of the 13th August
Image: Stellarium/IM
August - Find the globular cluster in Hercules and spot the "Double-double" in Lyra
Use binoculars to find the globular cluster M13 in Hercules and the "Double-double" in Lyra
Image: Stellarium/IM
There are two very nice objects to spot with binoculars in the south-eastern sky well after dark this month. Two thirds of the way up the right hand side of the 4 stars that make up the "keystone" in the constellation Hercules is M13, the best globular cluster visible in the northern sky.
Just to the left of the bright star Vega in Lyra is the multiple star system Epsilon Lyrae often called the double-double. With binoculars a binary star is seen but, when observed with a telescope, each of these two stars is revealed to be a double star - hence the name!
August 1st-3rd - after sunset: Mars.
Mars after Sunset
Image: Stellarium/IM
A vey last chance to spot Mars before it passes behind the Sun.
August 8th - before dawn: Jupiter and the Moon.
Jupiter and the Moon
Image: Stellarium/IM
This morning, if clear, and looking towards the East-Southeast before dawn one could spot Jupiter below the 3rd quarter Moon.
Aug 31st - before dawn: Saturn and the Moon
Saturn and the Moon
Image: Stellarium/IM
Looking towards the Southwest before dawn on could spot, if clear, Saturn to the right of the Full Moon. Actually a Supermoon!
August 26th - evening: The Hyginus Rille
Hyginus Rille location: IM.
This evening, should it be clear, is a superb time to view the Hyginus Rill as it will lie close to the terminator. For some time a debate raged as to whether the craters on the Moon were caused by impacts or volcanic activity. We now know that virtually all were caused by impact, but it is thought that the Hyginus crater that lies at the centre of the Hyginus Rille may well be volcanic in origin. It is an 11 km wide rimless pit - in contrast to impact craters which have raised rims - and its close association with the rille of the same name associates it with internal lunar events. It can quite easily be seen to be surrounded by dark material. It is thought that an explosive release of dust and gas created a vacant space below so that the overlying surface collapsed into it so forming the crater.
Hyginus Crater and Rille
M16, the Eagle nebula, imaged with the Faulkes Telescope
Messier 16 - The Eagle Nebula
Image: Daniel Duggan
Faulkes Telescope North.
The Eagle Nebula, M16, 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. It is a region of dust and gas where stars are now forming. The ultraviolet light from young blue stars is stripping the electrons from hydrogen atoms so this region contains ionized hydrogen and is called an HII region. As the electrons drop back down through the hydrogen energy levels as the atoms re-form, red light at the H alpha wavelength is emitted. This "true colour" image is composed of red, green and blue images along with a narrow band H alpha image. A Hubble image of the central region, called the "Pillars of Creation", has become quite famous but looks green/blue in colour. This is a false colour image where the H alpha image has been encoded as green!
Learn more about the Faulkes Telescopes and how schools can use them: Faulkes Telescope"
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 | third quarter |
|---|---|---|---|
| August 16th | August 24th | August 31st | August 8th |
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 9,550 pixels. The resolution of ~0.4 arc seconds 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 8 day old Moon
The 8 day old Moon imaged by Ian Morison.
This image was taken by the author on a night in March 2018 when the Moon was at an elevation of ~52 degrees and the seeing was excellent. This enabled the resolution of the image to be largely determined by the resolution of the 200 mm aperture telescope and the 3.75 micron pixel size of the Point Grey Chameleon 1.3 megapixel video camera. The use of a near infrared filter allowed imaging to take place before it was dark and also reduced the effects of atmospheric turbulence. The 'Drizzle' technique developed by the Hubble Space Telescope Institute (HSTI) was used to reduce the effective size of the camera's pixels to allow the image to be well sampled. Around 100 gigabytes of data, acquired over a 2 hour period, was processed to produce images of 54 overlapping areas of the Moon which were then combined to give the full lunar disk in the free 'stitching' program Microsoft ICE. A further HSTI development called 'deconvolution sharpening' was then applied to the image. The Moon's disk is ~6,900 pixels in height and has a resolution of 0.6 to 0.7 arc seconds. Interestingly, as seen in the inset image, the rille lying along the centre of the Alpine Valley is just discernable and this is only ~0.5 km wide! [Due to size limitations the large image is 2/3 full size.]
The Planets
A montage of the Solar System. JPL / Nasa
Jupiter
A Cassini image of Jupiter . Nasa
Jupiter is now visible in the eastern pre-dawn sky rising at midnight BST. At the start of the month it will have a magnitude of -2.59 and an angular diameter of 39.8 arc seconds. By month's end, it rises at 10pm BST and will be best seen in the Southeast around 4 am BST with an elevation of 52 degrees. By then, its brightness will have increased a touch to -2.61 and its angular size to 44 arc seconds.
Saturn
The planet Saturn. Cassini - Nasa
Saturn. Early this month Saturn may be spotted before dawn in the east-southeast having a magnitude of 0.58 having risen at 10:15 BST. Its angular size will then be 18.74 arc seconds with its rings spanning some 43.7 degrees. By month's end it rises as darkness falls and will be best seen in the South at 01:00 BST having an elevation of 26 degrees, then having a magnitude of 0.45 and an angular diameter of 19 arc seconds.
Mercury
Messenger image of Mercury Nasa
Mercury is not visible this month.
Mars
A Hubble Space Telescope image of Mars.
Jim Bell et al. AURA / STScI / Nasa
Mars. Coming towards the very end of its apparition, Mars can be seen low in the west as darkness falls in the first few days of the month with a magnitude of 1.77. Binoculars will almost certainly be needed to cut through the Sun's glare, but please do not use them until after the Sun has set.
Venus
Venus showing some cloud structure
Venus. will become visible looking East in the pre-dawn sky by around the 26th of the month having a magnitude of-4.4 and an angular diameter of 54 arc seconds. Only 6.3% of its disc will then be illuminated - a very thin crescent!
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-west 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