The Telescope

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

 

 

Constellations of the month

 

 
CURRENT MOON

Saturn

Saturn, was at opposition on the 27th of June and so will be visible in the south at an elevation of ~15 degrees after sunset at the beginning of August. Its disk has an angular size of 18 arc seconds falling to 17 during the month. Its brightness reduces from +0.2 to +0.4 magnitudes as the month progresses. The rings were at their widest some months ago and are still, at 26 degrees to the line of sight, well open and spanning ~2.5 times the size of Saturn's globe. Saturn, lying in Sagittarius, is close to the topmost star of the 'teapot' slowly moving in retrograde to within a few degrees of M8, the Lagoon Nebula, and M20, the Trifid Nebula. Sadly, atmospheric dispersion will thus greatly hinder our view and, as for Jupiter, it might be worth considering purchasing the ZWO Atmospheric Dispersion Corrector to counteract its effects.

Jupiter

Jupiter can be seen in the southwest soon after sunset at the start of the month. It shines at magnitude -2.1 (falling to -1.9 during the month) and has a disk some 38 (falling to 35) arc seconds across. Jupiter's equatorial bands, sometimes the Great Red Spot and up to four of its Gallilean moons will be visible in a small telescope. Sadly, moving slowly westwards in Libra during the month, Jupiter is heading towards the southern part of the ecliptic and will only have an elevation of ~15 degrees after sunset. Atmospheric dispersion will thus hinder our view and it might be worth considering purchasing the ZWO Atmospheric Dispersion Corrector to counteract its effects.

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Mars

Mars, moving in retrograde motion westwards in Capricornus made its closest approach to Earth since 2003 on the night of July 30th/31st. Mars begins the month rising just after sunset shining at its peak magnitude of -2.8 but this falls to -2.2 by month's end. Its angular size exceeds 24 arc seconds until August 8th and falls to 21 arc seconds by the start of September. With a small telescope it should (but see below) be possible to spot details, such as Syrtis Major, on its salmon-pink surface. From the UK, it will only reach an elevation of ~14 degrees when due south and so, sadly, the atmosphere will hinder our view. Another reason for purchasing a ZWO Atmospheric Dispersion corrector? As I write this in July, a dust storm obscures much of the surface - lets hope it clears during August.

Venus

Venus, can be seen low in the west after nightfall sinking towards the horizon as the month progresses. During August, its illuminated phase thins from ~57% to ~29% but, at the same time, the angular diameter of its disk increases from 20 to 29 arc seconds. The surface area reflecting the Sun's light becomes greater and so the brightness increases from -4.3 to an oustanding -4.6 magnitudes. Venus moves towards Spica in Virgo as August progresses and ends the month just one degree below the star. Sadly, however, they are then only ~10 degrees above the western horizon after sunset. .

Mercury

Mercury, having passed between the Earth and Sun (inferior conjunction) on August 9th, becomes visible after the 20th before reaching greatest elongation east of the Sun on August 26th. Then, some 18 degrees from the Sun, it rises before 5 am shining at magnitude zero.

The Night Sky In and Around Swindon August 2018

Slide Presentation

The following presentation was given at our meeting on the 18th May, 2018 by Rob Slack

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.


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.
Owl Nebul
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M97 - The Owl Planetary Nebula Lord Rosse's 1848 drawing of the Owl Nebula
The constellation Virgo

Virgo, rising in the east in late evening 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
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

August - observe Saturn


Saturn photographed by Damian Peach
Damian Peaches Website

Saturn reached opposition on the 27th of June, so is now low (at an elevation of ~14 degrees) in the west-southwest as darkness falls lying above the 'teapot' of Sagittarius. Held steady, binoculars should enable you to see Saturn's brightest moon, Titan, at magnitude 8.2. A small telescope will show the rings with magnifications of x25 or more and one of 6-8 inches aperture with a magnification of ~x200 coupled with a night of good "seeing" (when the atmosphere is calm) will show Saturn and its beautiful ring system in its full glory.

Compiled by Prof. Ian Morison
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 about 50 degrees from the "radiant" which lies between Perseus and Cassipeia. The really good news is that, this year, these nights are only a few days after New Moon on the 11th so that the Moon will have set by the time we should look out for meteors and 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.

The planets this month
As Saturn rotates quickly with a day of just 10 and a half hours, its equator bulges slightly and so it appears a little "squashed". Like Jupiter, it does show belts but their colours are muted in comparison.

The thing that makes Saturn stand out is, of course, its ring system. The two outermost rings, A and B, are separated by a gap called Cassini's Division which should be visible in a telescope of 4 or more inches aperture if seeing conditions are good. Lying within the B ring, but far less bright and difficult to spot, is the C or Crepe Ring.

Due to the orientation of Saturn's rotation axis of 27 degrees with respect to the plane of the solar system, the orientation of the rings as seen by us changes as it orbits the Sun and twice each orbit they lie edge on to us and so can hardly be seen. This last happened in 2009 and they are currently at an angle of 26 degrees to the line of sight. The rings will continue to narrow until March 2025 when they will appear edge-on again.

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.

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
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
August - observe Mars
Mars came to its closest opposition to Earth since 2003 on the 27th July but, sadly two things conspire to limit our views. From the UK its maximum elevation when on the meridian will be only 12 degrees when observed from a latitude of +52 degrees. Thus the atmosphere will hinder our view and the use of an Atmospheric Dispersion Corrector may well help to alleviate its effects. The second problem is that, as sometimes happens, Mars is now suffering a major dust storm which, at the end of July, was making it very difficult to observe any features on the surface. These can happen every six to eight years and can last for several months. A small scale dust storm began on May 30th and, by the 20th of June, had engulfed the whole planet. Sadly, it could take as long as September for the dust to settle thus greatly inhibiting our view of Mars this apparation. However, it does look as though the South Polar Cap is still visible. Lets just hope that the dust storm subsides in time for other details on the surface such as Syrtis Major and the Hellas Basin to become visible in small telescopes. On the night of August 11th, these should be facing the Earth.
Compiled by Ian Morison - Jodrell Bank Centre for Astrophysics