WHAT'S UP THIS MONTH - OCTOBER 2019
(Link to What's Up September 2019)
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THESE PAGES ARE INTENDED TO HELP YOU FIND YOUR WAY AROUND THE SKY
The chart above shows the night sky as it appears on 15th October at 21:00 (9 o'clock) in the evening 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 10 o'clock BST at the beginning of the month and at 8 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 easy to find. This month it is 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.
Remember British Summer Time (BST) ends on 27th OCTOBER
EXPLORING THE NIGHT SKY THIS MONTH
The Southern Night Sky during October 2019 at 21:00 BST
The chart above shows the night sky looking south at about 21:00 BST on 15th October. 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 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 Sagittarius (the Archer) just moving over the western horizon, Capricornus (the Goat), Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram) and Taurus (the Bull) in the east.
Just disappearing over the south western horizon is the constellation of Sagittarius (the Archer). It is really a southern constellation but we can see the upper part creep along the horizon during the summer. The central bulge of our galaxy is located in Sagittarius so the richest star fields can be found in the constellation along with many of the beautiful and interesting deep sky objects that we seek out. Saturn is currently in Sagittarius.
The summer constellations are still prominent in the night sky lead by Hercules (the Hunter). Following Hercules is the Summer Triangle with its three corners marked by the bright stars: Deneb in the constellation of Cygnus, Vega in Lyra, and Altair in Aquila. The Summer Triangle is very prominent and can be used as the starting point to find our way around the night sky. See the previous pages. The Milky Way (our Galaxy) flows through the Summer Triangle passing through Cygnus, down to the horizon in Sagittarius.
The Milky Way flows north from the Summer Triangle through the rather indistinct constellation of Lacerta (the Lizard), past the pentagon shape of Cepheus and on through the ‘W' shape of Cassiopeia (a Queen) .
Just visible at the top of the chart above is the fairly faint constellation of Ursa Minor (the Little Bear) also called the Little Dipper by the Americans. Although Ursa Minor may be a little difficult to find in a light polluted sky it is one of the most important constellations. This is because Polaris the North Star is located in Ursa Minor. Polaris is the star that is located at the approximate point in the sky where an imaginary line projected from Earth's North Pole would point to. As the Earth rotates on its axis the sky appears to rotate around Polaris once every 24 hours. This means Polaris is the only bright star that appears to remain stationary in the sky as Earth rotates.
To the East 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.
Coming into view in the east is the constellation of Taurus (the Bull). The most obvious star in Taurus is the lovely Red Giant Star called Aldebaran. It appears slightly orange to the unaided eye (we call the ‘naked eye') but it is very obviously orange when seen using binoculars or a telescope. Aldebaran is located at the centre of the ‘flattened' X shape formed by the brightest stars in Taurus. At the end of the top right (upper west) arm of the ‘X' is the beautiful Open Star Cluster Messier 45 (M45) known as the Pleiades (or the Seven Sisters). It really does look magnificent using binoculars.
CONSTELLATIONS OF THE MONTH – PEGASUS AND ANDROMEDA
The constellations of Pegasus and Andromeda to the east (left) of the Summer Triangle
The constellations of Pegasus and Andromeda share and are joined at the star Alpheratz. Alpheratz is actually designated as belonging to Andromeda but looks to be more a part of Pegasus as it is required to complete the familiar ‘Great Square of Pegasus'. The Great Square is larger than may be expected which sometimes makes it a little difficult to initially identify. However once it has been identified it is easy to find again in a clear dark sky.
The constellation of Pegasus
Pegasus is named after the mythical winged horse and with Andromeda included to provide the wings and a lot of imagination the stars could be said to resemble the flying horse. The square generally is used to represent the body of the horse and the three lines to the west (right) of the stars Scheat and Markab do look a little like the horse's legs.
The square can be used to judge the seeing condition of the night sky. Under perfect conditions about ten stars can be seen, using our ‘naked eyes', inside the square so 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 than five 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). It is a lovely sight to see in a medium to large telescope.
Messier 15 (M15) the Globular Cluster in Pegasus
To find M15 start at the star Markab, located at the bottom right of the Great Square (see the preceding charts). Follow the fainter line of stars to the west (right) to the star Baham then North West (up and right) to the star Enif, see the charts above and the previous column. Continue the imaginary line on for about the same distance to find the fuzzy patch that will be the Globular Cluster M15. M15 can just be seen using binoculars but really needs a telescope.
Globular Clusters are generally spherical clusters of between 10,000 and 1 million stars. They are thought to be the central core of smaller galaxies that have had their outer stars torn away in close encounters with our Giant Spiral Galaxy that we call the Milky Way. M15 is the second brightest Globular Cluster that can be seen from the UK. M13 in the constellation of Hercules is the largest and brightest. It can be seen using binoculars but looks beautiful when using a telescope.
There is thought to be about one hundred Globular Clusters orbiting the centre of our Galaxy (The Milky Way). They do not move round in the flat disc structure of the Galaxy, like most of the other material. They appear to follow random orbits is a sort of halo surrounding the Galaxy. Amazingly Globular Clusters can and do even pass through the spiral arms in the flat disc structure of the Galaxy. As the stars in the globular cluster and the galaxy are so far apart compared to their size they very rarely if ever collide. The stars just past through almost ghost like.
SPECIAL CONSTELLATION OF THE MONTH – ANDROMEDA
The constellation of Andromeda is host to the only ‘naked eye' Galaxy that we call Messier 31 (M31). It is the most distant object that can be seen with our naked eyes (2.4 million light years away). It is quite easy to find using binoculars and is getting well placed at this time of year.
The easiest way to find M31 is to first locate the Great Square of Pegasus. Once the square is found the pointer to Andromeda is the top left star of the square named Alpheratz. Strangely Alpheratz is officially not part of Pegasus but is designated as Alpha (a) Andromedae. From Alpheratz follow the fairly obvious line of stars to the left (east). Locate the second star in the line which is shown as Mirach on the chart above. From Mirach follow a slightly fainter short line of stars to the north (above) Mirach and up to the second star. Just to the right of this star is the faint fuzzy patch of light that is M31 the Great Andromeda Galaxy. See the chart above.
Messier 31 (M31) as seen in the sky (with lines and names added)
The Image above shows M31 imaged through a small telescope. The image is much clearer than can be hoped to be seen with the naked eye. However a pair of binoculars will enable the galaxy to be seen looking similar but not so bright and less stars. A small telescope will show a cigar shaped hazy patch with a brighter spot in the centre. Larger telescopes will show it more clearly but photographic imaging is required to reveal its true nature. See the image below.
Messier 31 (M31) the Great Spiral Galaxy in Andromeda
At the end of the lower line of stars that mark out the constellation of Andromeda is the star Almach or (Almaach). It is a beautiful example of a pair of stars that are not physically related. They are thought to be at different distances but appear to be in the same ‘line of sight' as seen from Earth. The apparently brighter golden coloured star is thought to be located much nearer to us than the apparently fainter blue star. The blue star is in fact a Blue Giant, a very hot and powerful star that is many thousands of times brighter than the golden star but much further away. A telescope is required to separate this beautiful double.
Almach the ‘line of sight' double star in Andromeda
THE SOLAR SYSTEM THIS MONTH
MERCURY will not be observable this month as it will be too close to the Sun. It was in conjunction with the Sun (passing just above the Sun) on 4th September. It is very close to the southern horizon in the glare of sunset.
Mercury and Venus at sunset on 15th October
VENUS will not be observable this month as it will be too close to the Sun and very low on the south western horizon at sunset. It was in conjunction with the Sun (passed just above the Sun) on 14th August. See the chart above.
Mars rising at sunrise in the east
MARS will not be observable this month as it will be too close to the Sun as it rises in the east. It was in conjunction with the Sun (passing just above the Sun) on 2nd September. See the chart above.
JUPITER is now past its best for this year and setting over the western horizon soon after sunset. It has been very low in the sky this year and has been rather disappointing in the dirty and turbulent air close to the horizon.
SATURN will be in the in the south as the sky darkens and is following Jupiter along the ecliptic. Saturn is also low and in the murky and turbulent air close to the southern horizon. It is still possible to see the ring system although it will appear unstable due to the air movement close to the horizon. It will require a small telescope 75mm to 100mm and a magnification of about 100x to see the rings well. Saturn's largest moon Titan will also be visible in a telescope but the fainter moons will be difficult to see even using a larger telescope. See the chart below.
Jupiter and Saturn in the south west at 19:00 in the beginning of October
The two Gas Giant planets have not been good for observing this year due to their very low position above the horizon. This low altitude has spoiled the view because the air close to the ground is affected by the heat rising from the ground and producing turbulence that causes the image to wobble. The problem is compounded by the thickness of the air we have to look through. When we look directly up over our head we are peering through about 100km of atmosphere but the upper 50km is very thin. When we look through the atmosphere close to the horizon we must peer through about 300km of the thickest part of the atmosphere.
Unfortunately there is not a lot we can do about ‘seeing' conditions close to the horizon and have to accept the poor quality of the view. However there are few things we can do to make the best in these bad conditions. Firstly we will need at least a small telescope to see any detail on Jupiter and Saturn.
Dust Cover and Cap
Dust Cover with Cap removed
Jupiter appears larger and brighter than Saturn so more detail can be seen. However the additional brightness will cause too much glare so an aperture reducer should be used. Most telescopes are supplied with a Dust Cover with a removable cap that can be used to reduce the amount of light entering the telescope. Fit the Dust Cover over the open end of the telescope and remove the small cap to reduce the amount of light entering the telescope. See above.
The aperture reducer should not be required to observe Saturn . It may also be found that a lower magnification will improve the image and reduce the effect of air turbulence. Refraction of the light from the planet will also cause colour separation in the image. This is seen as red and blue fringes on opposite sides of the image. This effect will also be reduced by using a lower magnification.
Unfortunately Jupiter is now too close to the south western horizon and the image will be very poor. It will need to be observed as soon as it is dark enough and a clear view to the horizon is essential. Jupiter will set over the horizon at about 20:15. Saturn is about two hours behind Jupiter so it will be in view longer and will initially be higher. The ring system and moons will be difficult to resolve. Not very good prospects but it is the last chance this year.
URANUS is in its best position for observing this month. The Ice Giant Planet will be in opposition to the Sun (due south at midnight – 24:00 GMT) on 28th October when it will be at its best position for observation this year. It will be visible during in the evening using a small telescope as a slightly fuzzy blue, star like, object. A larger telescope with a magnification of 100x or more will show it as a small blue/green disc. See the chart below
Uranus, Neptune and Saturn in the south at 21:00
NEPTUNE was at opposition (due south at midnight – 01:00 BST) on 10 th September and at its best position for observation this year. A medium sized telescope (100mm to 150mm) will be needed to show Neptune as a small blue/green disc using a magnification of 150x but it is small and difficult to find. See the chart above.
There may still be some occasional sunspots to see even though the active phase of the Solar Cycle is now over.
The Sun rises at 07:00 BST at the beginning of the month and at 06:45 GMT by the end of the month. It will be setting at 18:35 BST at the beginning and 16:45 GMT by the end of the month. 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/ .
THE MOON PHASES IN OCTOBER
First Quarter will be on 5th October
Full Moon will be on 13th October
Last Quarter will be on 21st October
New Moon will be on the 28th October
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