Whats Up

The chart above shows the whole night sky as it appears on 15th September at 22:00 (10 o'clock) British Summer Time (BST). As the Earth orbits the Sun and we look out into space each night the stars will appear to have moved across the sky by a small amount. Every month Earth moves one twelfth of its circuit around the Sun, this amounts to 30 degrees each month. There are about 30 days in each month so each night the stars appear to move about 1 degree. The sky will therefore appear the same as shown on the chart above at 9 o'clock BST at the beginning of the month and at 11 o'clock BST at the end of the month. The stars also appear to move 15º (360º divided by 24) each hour from east to west, due to the Earth rotating once every 24 hours.

The centre of the chart will be the position in the sky directly overhead, called the Zenith. First we need to find some familiar objects so we can get our bearings. The Pole Star Polaris can be easily found by first finding the familiar shape of the Great Bear ‘Ursa Major' that is also sometimes called the Plough or even the Big Dipper by the Americans. Ursa Major is visible throughout the year from Britain and is always quite easy to find. This month it is located high in the North West. Look for the distinctive saucepan shape, four stars forming the bowl and three stars forming the handle. Follow an imaginary line, up from the two stars in the bowl furthest from the handle. These will point the way to Polaris which will be to the north of overhead at about 50º above the northern horizon. Polaris is the only moderately bright star in a fairly empty patch of sky. When you have found Polaris turn completely around and you will be facing south. To use this chart, position yourself looking south and hold the chart above your eyes.

The planets visible in the evening sky this month: Saturn, Neptune, Jupiter, Uranus and Mars.

The chart above shows the night sky looking south at about 22:00 BST on 15th September. West is to the right and east to the left. The point in the sky directly overhead is known as the Zenith and is shown (in red) at the upper centre of the chart. The curved brown line across the sky at the bottom is the Ecliptic or Zodiac. This is the imaginary line along which the Sun, Moon and planets appear to move across the sky. The brightest stars often appear to form a group or recognisable pattern; we call these ‘Constellations'.

Constellations through which the ecliptic passes this month are: Libra (the Scales), Scorpio (the Scorpion) Sagittarius (the Archer), Capricornus (the Goat), Aquarius (the Water Carrier), and Pisces (the Fishes).

Prominent in the southern sky is the Summer Triangle that dominates the Summer Sky and is described in detail on the following pages. The term Summer Triangle was first suggested by Sir Patrick Moore and is defined by three obvious bright stars: Deneb in the constellation of Cygnus, Vega in Lyra, and Altair in Aquila. The Milky Way (our Galaxy) flows through the Summer Triangle and passes through Aquila and Cygnus. The Summer Triangle is bigger than may be expected but once it has been found it is very easy to find again.

As the Summer Triangle is so easy to find it is very useful to use as a starting place for finding our way around the night sky.

To the west (right) of the Summer Triangle and almost overhead is the constellation of Hercules (the Strong Man). Hercules has a distinctive distorted square shape, at its centre, called the ‘Keystone'. This is due to its resemblance to the centre stone of an arch or bridge. The jewel of Hercules is without doubt the Great Globular Cluster, Messier 13 (M13) that can be found in the western vertical imaginary line forming the ‘Keystone'.

It is just visible using a good pair of 9 x 50 binoculars. The spherical cluster, of about a million stars can be seen using a 90mm f 10 telescope but will look even more impressive when using a larger telescope.

To the west of Hercules and moving towards the western horizon is the bright orange coloured star called Arcturus in the constellation of Boötes. Arcturus is a star similar to our Sun but more advanced and is developing into a Red Giant star that is nearing the end of its ‘life' as a normal star. It has used almost all of its Hydrogen fuel and has expanded to become a Red Giant, 25 times the diameter of our Sun. At the moment it shines 115 times brighter than our Sun but it is destined to collapse and become a White Dwarf and Planetary Nebula.

To the East (left) of the Summer Triangle is the constellation of Pegasus (the Winged Horse). The main feature of Pegasus is the square formed by the four brightest stars. This asterism (shape) is known as the Great Square of Pegasus. The square is larger than might be expected but once found is easier to find again.

The square can be used to judge the seeing condition of the night sky. Under perfect conditions about ten stars can be seen inside the square this would indicate a very good night for observing. If three to five stars can be seen then conditions will still be good. If fewer or none can be seen then stick to looking at the Moon or planets. There is a very nice Globular cluster in Pegasus it is known as Messier 15 (M15) and is a lovely sight to see in a medium to large telescope.

The Ecliptic is low in the sky during the summer months so the Moon and planets appear close to the southern horizon. Saturn and Jupiter are well placed this year but due to their low altitude will not be at their best for observation. However the thick, murky and turbulent air will cause the planets to appear quite unsteady.

The chart above shows the sky around the Summer Triangle. The term ‘Summer Triangle' was suggested by Sir Patrick Moore and has now become the best known feature of the summer night sky. The corners of the imaginary triangle are positioned on the three obvious bright stars: Deneb in the constellation of Cygnus, Vega in Lyra, and Altair in Aquila. The Milky Way (our Galaxy) flows through the Summer Triangle and passes through Aquila and Cygnus.

The constellation of Aquila (the Eagle) is found at the bottom corner of the Summer Triangle. There are no interesting objects in Aquila but the one bright star, Altair, has a fainter star above and below it that makes it quite easy to find.

The constellation of Cygnus (the Swan) is located at the top of the Summer Triangle. The brightest star in Cygnus is Deneb that denotes the upper point of the Summer Triangle and represents the Swan's tail. The wings spread out from the star Sadr and the head is marked by Albireo. Deneb is one of the largest and brightest stars in our vicinity in our galaxy the Milky Way and is classified as a Supergiant. It is about 25 times more massive than our Sun and has a diameter 60 times that of our Sun. It is located 3000 light years away. As it is so much larger than our Sun it consumes its Hydrogen fuel much faster and consequently shines 60,000 times brighter.

Cygnus (the Swan) does actually resemble the swan it is supposed to represent. We start at the bright star Deneb which marks the tail of the swan. From the fairly bright star Sadr the wings are spread out to each side and the long neck of the swan stretches on to Albireo.

Albireo can be seen as a beautiful double star when viewed through a telescope. One star is bright and gold in colour the other is fainter and distinctly blue. This is not a true pair they just happen to be in the same line of sight. Although the blue star is much bigger and brighter than the golden coloured star it is a lot further away from us. This type of double star is much rarer than a pair of stars that are associated and linked by their common gravity and orbiting a common centre of gravity.

The constellation of Lyra (the Harp) is located to the west (right) of Cygnus but is much smaller. The most obvious feature of Lyra is the very bright star Vega that is located the top right corner of the Summer Triangle. Vega is the fifth brightest star in our sky with a magnitude of 0.4. It is located at a distance of 25.3 light years from us and is thought to be 3.2 times the diameter of our Sun and 58 times brighter. Inferred detectors on the IRAS satellite have detected a ring of dust around Vega that may indicate planets are forming around the star.

The main asterism (shape) of Lyra is composed of a line of three stars with Vega in the centre and a group of four fainter stars that form a parallelogram shape that is better known as the ‘Lozenge'.

To the south east of the very bright star Vega is the lozenge shaped asterism comprised of four stars . Between the two lower stars: Sulafat and Sheliak is the Messier object M57. This is a ‘Planetary Nebula' which has nothing to do with a planet. It is in fact a dying star that was similar to our Sun but older. The star had used most of its Hydrogen fuel and expanded to form into a Red Giant. After passing though that red giant phase it gently collapsed to become a White Dwarf. The very thin outer mantle of the red giant drifted away into space as the star collapsed. The white dwarf is now surrounded by a bubble of gas and dust. It looks like a small ‘smoke ring' when seen through a telescope but can't be seen using normal binoculars.

There are two other constellations that are located within the Summer Triangle. They are both small and comprised of relatively faint stars but are worth seeking out using binoculars.

Sagitta is good fun to find using just our eyes or small binoculars because it really does look like an ‘arrow'. It is composed of three stars that look like the shaft of the arrow and two stars that resemble the flight feathers.

The real beauty of Sagitta is how it looks using small binoculars but it does host one messier object this is M71 also known as NGC 6838. This is a rather nice but small and faint Dwarf G lobular Cluster that does need a medium to large sized telescope to see well.

Vulpecular is a quite indistinct constellation located in the Summer Triangle, see the chart above. The pattern of stars that denotes Vulpecular is just three rather faint stars that do not resemble anything like the fox that it is supposed to represent. However it is host to a bright planetary nebula (M27) that can just be seen using a good pair of binoculars. It is also known as the Dumbbell Nebula but looks more like a butterfly. It is a similar object to M57 but has two interesting lobes.

It is thought that as the original star began to collapse to form a White Dwarf the surrounding gas was in influenced by either a strong magnetic force in the star or the presence of one or more planets around the star. This may have caused the gas to be formed into the two lobes that we can see.

Between the small constellations of Vulpecula and Sagitta is a rather delightful ‘Asterism' (pattern of stars) known as the Coat Hanger. It is best seen using binoculars or a small telescope (using a low power eyepiece). It is located about half way between the ‘tail feathers' of Sagitta (the Arrow) and the western (right) star of the three ‘brightest' stars in Vulpecular (the Fox).

The Coat Hanger (also known as C399) is a sparse Open Cluster of ten 5th to 7th magnitude stars in a pattern that does resemble an up-side-down Coat Hanger. It is easily seen using a pair of 8x50 binoculars and looks very pleasing to the eye. There are other smaller stars in the cluster but the main interest is the Coat Hanger shape.

To find the Coathanger, first locate the two tail feather stars of the Arrow then slowly sweep the binoculars up and to the west (right) and the Coat Hanger should come into view. The asterism is too large to fit into the field of view of most telescopes but looks good in a finderscope.

Just to the east (left) of the lower part of the Summer Triangle is the lovely little constellation of Delphinus (the Dolphin). It is small but can be seen easily with the unaided eye from a dark area when there is a clear sky.

The asterism (shape) of Delphinus is comprised of a four stars that form a neat diamond shape and a fifth star a short distance from the diamond shape that completes the dolphin's body and tail. With a little imagination it does look remarkably like a dolphin leaping out of the water.

Once we have identified and explored the Summer Triangle we can venture out to identify the constellations that surround the Summer Triangle.

Further to the west is a beautiful red giant star that is moving towards the western horizon this is the bright orange coloured star called Arcturus in the constellation of Boötes. Arcturus is a star similar to our Sun but more advanced and is developing into a Red Giant star that is nearing the end of its ‘life' as a normal star.

Finally, after exploring the Summer Triangle it is well worth spending a little time to marvel at the Milky Way. This is our Galaxy which our Sun is just one of the 200 billion (or more) stars that reside in it. On a dark clear night the misty cloud of stars can be seen as they cascade down through the Summer Triangle. If we start at the very distinctive ‘W' shape of Cassiopeia and pass through the Zenith (the point directly overhead) we pass into Cygnus the Swan. The Milky Way passes right down the centre of the Summer Triangle to exit at the bottom of the triangle marked by the star Altair (see the chart above). The centre of our Galaxy is located in the constellation of Sagittarius that is sitting on the south western horizon see the chart on page 1. The best way to appreciate the Milky Way is to lay flat on a garden lounger or just lie on the patio and look up. Binoculars can be also used to see the clouds of stars in the Milky Way.

The immediate area around us in space and where we live is called our ‘Solar System'. This is the whole area around us that is dominated by the star that we call The Sun. The bodies that we call Planets are objects that orbit our star. The Planets have cleared paths from the original disc of gas and dust and have grown massive enough to become spherical. Our Solar System has eight main planets that, in order out from the Sun, are called: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. They orbit the Sun anticlockwise as we look at the chart.

The chart above shows the location of the Inner Planets in their relative positions compared to the Sun and our viewpoint (following the arrows) on Earth this month. The four inner planets Mercury, Venus, Earth and Mars are the smallest and are comprised of rock with an Iron core. They are clustered closely around the Sun with their orbits spaced about 50 million kilometers apart. They are called the ‘Terrestrial Planets' because they are ‘Earth like'. Earth is the only Terrestrial Planet with a Moon but Mars does have two very tiny moons that may be captured asteroids. Moons are objects that orbit the planets.

The two innermost planets Mercury and Venus orbit the Sun inside the orbit of Earth. So we always see them in the general direction of the Sun. As they orbit the Sun we see them illuminated from different directions so they show phases like we see on our Moon. Mars has its orbit outside of Earth so we always see it with one side almost fully illuminated.

Beyond the orbit of Mars are the two Gas Giant Planets called Jupiter and Saturn. Jupiter is the largest planet and is comprised mainly of Hydrogen gas with traces of other gases. Jupiter has beautiful cloud formations and has four large moons that can be seen using a telescope. Saturn is the second largest planet and is famously the planet with a beautiful ring system. The ring system and one of Saturn's many moons called Titan are visible using the smaller telescopes previously mentioned. Saturn is also comprised mainly of Hydrogen gas and has surface markings but they are not as noticeable as those seen on Jupiter. Details in the ring system can be seen using a larger telescope and five or six of the smaller moons may visible on a clear night.

The orbits of the outer planets are much further apart than the Inner (Terrestrial) Planets so there is a noticeable difference in brightness and size between Jupiter and Saturn. This is because the orbit of Saturn is about as far from Jupiter as Jupiter is from us therefore Saturn appears less than half the diameter and much fainter.

The outer most planets are Uranus and Neptune that are known as the Ice Giants. Jupiter and Saturn are over ten times the diameter of Earth but Uranus and Neptune are about four times the diameter of Earth so are still regarded as giants. Both of the Ice Giants appear blue but look more like ‘fuzzy stars' than the other planets.

The chart above shows the location of the planets along the Ecliptic in the early morning sky. The sky has been darkened to make the planets visible. The planets are: (in order as they appear) Saturn, Neptune, Jupiter, Uranus and Mars. Venus and Mercury are close to the Sun this month. The planets appear low in the sky, in the bright morning or evening sky so are not well positioned for observing.

MERCURY will be at Inferior Conjunction with the Sun on 23rd September this means it will be passing in front of the Sun. After conjunction it will move into the morning sky and will rise just before the Sun. Mercury will be at its greatest westerly elongation on 8th October when it will be at its apparent furthest point from the Sun.

VENUS rises about one hour before the Sun climbs over the eastern horizon at the beginning of the month. It is looking very bright but low in the east before sunrise. It is moving back towards the Sun and Superior Conjunction (behind the Sun) on 22nd October so it appears smaller and will appear in its gibbous phase. As it is located on the other side of the Sun it appears small and will be close to the Sun and quite difficult to see.

MARS will be best seen from midnight in the east until sunrise. It is still some distance away but is approaching its closest position when it will be at Opposition on 8th December. The image below gives an approximation of how Mars will appear using a medium sized telescope.

Mars will be at its best during December when it will be at or close to its opposition. Although Mars will not be as close to Earth as it can be, it will be high in the sky and away from the turbulent and contaminated air close to the horizon. So we should be able to obtain some good views of the Red Planet around Christmas time.

JUPITER will be at Opposition (directly in line with the Sun and Earth) at midnight on 26th September. At this point Jupiter will be at its best position for observing and will be a little higher in the sky than it was last year. So it will be a little clearer as it will be higher above the horizon and in slightly clearer and less turbulent air. The cloud markings and the four brightest (Galilean) moons will be visible, using a smaller telescope, even with the turbulent air above the horizon.

The image below shows the kind of view we can expect using a medium sized telescope (150mm) using a high magnification eyepiece on a good night. For those with a smaller telescope, do not feel disappointed that the view is not as good as shown in magazines or on the internet. The important thing is that we are using ‘our own' telescope to see this beautiful object. The light from the planet has travelled through space and has entered our eye to produce a real image on our retina.

One of the most interesting things to do when observing the planets is to monitor the movements of Jupiter's four largest moons. This can be done with any good quality telescope whatever size it is. Obviously the bigger the telescope used the better the view will be but it is good fun whatever telescope is used.

The images below show how the positions of the moons change from day to day. Each moon can appear on either side of Jupiter and there can be combinations of the numbers of moons to each side. On 1st September three moons will be to the left and one to the right. On 4th September all the moons will be to the left with no moons to the right of the planet. Even using a small telescope the positions of the moons can be recorded using hand drawn sketches in a sketch pad. But be sure to mark the time and date.


Jupiter's moons on 1st September	Jupiter's moons on 4th September

We can also look closer at Jupiter and its moons and see that the moons can pass in front of the planet or pass behind. A smaller telescope will need to be fitted with its highest magnification (lowest number - 10mm for example). In the images below the first image shows the moon Io approaching Jupiter at 21:00 on 2nd September. The second image shows the shadow of Io imposed on the cloud tops of Jupiter. In reality Io will not be visible when it is directly in front of Jupiter the surface of Jupiter is too bright and drowns out the light from Io.

The very black shadow of the moon can easily be seen using a telescope. In image 3 the shadow is moving towards the right limb of Jupiter. Image 4 catches the moment that the shadow leaves the surface of Jupiter.


Io on 2nd September at 21:00	Io on 2nd September at 22:00

Io on 2nd September at 23:00	Io on 2nd September at 24:00

When a moon passes behind the planet it can be interesting to check the predicted time that the moon is due to emerge at the other side of the planet. We will need an accurate clock to do this. We can use a Planetarium application to predict all of these events. The images above were created using Starrynight. Stellarium can be downloaded free from the internet

SATURN is the first planet to rise over the eastern horizon so it will be seen very low in the south eastern sky as soon as it gets dark. It will be very low over the south eastern horizon at the beginning of September but the evenings will become darker earlier and Saturn will appear higher towards the end of the month.

Saturn will look small in a small telescope and not much bigger in a medium sized telescope but the ring will be visible even using a small beginner's telescope. The view of Saturn is very dependent on the seeing conditions. This is the term used by astronomers to describe how clear the sky appears. This depends on the brightness of the sky, how transparent it appears and how steady the atmosphere is. The image above was taken on a night when the ‘seeing' was very good. The shadow of the planet can be seen on the ring to the left of the planet.

The Cassini Division (gap in the ring) can be seen quite clearly. The ring is easier to see when Saturn is at its maximum tilt but becomes very difficult to see when the tilt is at minimum. When our view is edge on the ring becomes very difficult to see and all but disappears for a few of days. Although the ring is 282,000 km in diameter it is only about 100 meters thick.

URANUS is just observable this month as it was in conjunction with the Sun on 5th May. It rises in the east just as the sky darkens. Uranus will be best seen later is the night as it rises higher in the sky. It will be best at about 04:00 and just before sunrise.

NEPTUNE rises at about 19:10 so will be moving into the sky as the Sun sets. It will still be difficult to see in the bright late summer sky and will need a telescope to see looking like a small blue ‘fuzzy' star.

The Sun rises at about 06:20 BST at the beginning of the month and 6:50 BST by the end of the month. It sets at 19:30 at the beginning of the month and 18:50 at the end of the month. There have been a lot of very nice Sunspots and even some impressive groups of sunspots recently.

Sun spots can be seen and studied using most telescopes. However the telescope must be fitted with a special Solar Filter. This filter must be a specially manufactured solar filter and no other type of filtering device can be used. This special filter fits over the front of the telescope to hugely reduce the amount of sunlight that can enter the telescope. The telescope can be used as normal but only the Sun is bright enough to be visible through the filter.

Sunspots and other activity on the Sun can be followed live and day to day by visiting the SOHO website at: http://sohowww.nascom.nasa.gov/ .

There have been some very nice sunspots and groups of sunspots recently. These sunspots are caused by the magnetic forces in the Sun when they react with the upper layers of the Sun. The magnetic field causes an indentation that can reveal a slightly cooler and less bright layer beneath the surface. The sunspots below are larger than the size of Earth.


Uranus imaged Kyle Edwards		Neptune Imaged Kyle Edwards