WHAT'S UP THIS MONTH - NOVEMBER 2019
Special event Transit of Mercury (See the Solar System this month)
(Link to What's Up October 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 November at 21:00 (9 o'clock) in the evening Greenwich Meantime Time (GMT). 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 GMT at the beginning of the month and at 8 o'clock GMT 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 east. 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.
Planets observable this month: Uranus and Neptune.
EXPLORING THE NIGHT SKY THIS MONTH
The Southern Night Sky during November 2019 at 21:00 BST
The chart above shows the night sky looking south at about 20:00 GMT on 15th November. 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 Sagittarius (the Archer) just moving over the western horizon, Capricornus (the Goat), Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram), Taurus (the Bull) and Gemini (the Twins).
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 early night sky led 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. The Milky Way (our Galaxy) flows through the Summer Triangle passing through Cygnus, down to the horizon through Altair in the lower part of the Summer Triangle.
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) .
At the top of the chart above is Polaris in the 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 (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.
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.
CONSTELLATION OF THE MONTH – TAURUS (the Bull)
The constellation of Taurus
The chart above shows the constellation of Taurus the Bull. There are many different representations of Taurus but he is generally shown with his horns tipped by the stars at the end of the obvious ‘>' shape. The bright red star Aldebaran is normally used to show the bull's eye.
An illustration of the constellation of Taurus
With a little imagination Taurus appears to be charging Orion in the illustration. It sits on the Ecliptic and is one of the star signs of the Zodiac. The asterism (shape) used to identify Taurus resembles a stretched ‘X'.
The bright red star Aldebaran is located at the centre of Taurus. It is easy to find and therefore helps to identify the constellation of Taurus. It is in fact a Red Giant Star and that is why it appears distinctly orange. A Red Giant is a star similar to our Sun (perhaps a little larger) that is approaching the end of life as a normal star. It has used up most of its Hydrogen fuel and has swollen into a giant . Its outer layers are now stretched over a larger area so the available heat is also spread over a bigger area so the surface is cooler and appears orange in colour . Aldebaran is not a true member of the Hyades cluster it is located at about half the distance to the Hyades and is just in the same line of sight.
Surrounding the bright red star Aldebaran is an Open Cluster of Stars known as the Hyades. It is an older cluster so its stars have begun to disperse. The Hyades star cluster is estimated to be about 400 billion years old. It is also quite far away from us so the stars appear quite faint. In a dark Moonless sky the cluster can be seen with the naked eye but is best seen using binoculars. The cluster is large, at 3.5° in diameter (about 7 Moon diameters) and well dispersed.
The Open Star Clusters Hyades and Pleiades
The real jewel of Taurus is without doubt the beautiful Open Cluster, Messier 45 (M45) also called the Pleiades or the Seven Sisters. Messier 45 is a relatively young Open Cluster with its stars estimated to be about 100 million years old. An Open cluster is created as stars form in a giant cloud of gas and dust called a ‘Nebula'.
M45 is easily visible to the naked eye initially looking like a ‘fuzzy' patch of light. A longer look will reveal a cluster of up to seven stars. Using a good pair of binoculars many more stars will be seen. There are in fact about 300 bright young stars in the cluster and possibly another 1000 smaller stars. The cluster is estimated to be about 100 million years old. M45 is one of the closest open clusters to us at 400 light years.
The Pleiades look brighter than the stars of the Hyades because they are very bright large young stars and are relatively close to us. The largest is Alcyone which is 10 times the mass of our Sun and 1000 times brighter. The larger and brighter stars of the Pleiades are also rotating very fast. The fastest is Pleione which is rotating 100 times faster than our Sun.
Messier 45 (M45) the Pleiades (Seven Sisters)
The stars of the Pleiades cluster would have formed from the gas and dust of a Nebula. Gravity draws the atoms of the Nebula together to form denser clumps of gas that become ever denser. Eventually the gas is squeezed into dense spheres where the pressure and high temperature at the core causes atoms to combine through Nuclear Fusion. As Hydrogen atoms are fused into Helium. Heat is produced and the sphere becomes a shining star. Any left-over gas and dust is blown away by intense radiation from the young stars and a cluster of new stars is revealed. This type of star cluster is called an ‘Open Cluster'.
The biggest and brightest stars of M45 (the Seven Sisters) have been named after seven Pleiades sisters from Greek Mythology. They were the seven daughters of the Titan called Atlas and the sea-nymph Pleione and were born on Mount Cyllene.
Impressive as they are, the Seven Sisters are just the brightest (naked eye) stars in a cluster of around 250 young stars. In the images above the Seven Sisters appear to be surrounded by gas remaining from the original nebula. However it is now thought the cluster is just passing through a cloud of Hydrogen gas in space.
It is thought that all stars originated and formed in a Nebula, including our own star the Sun. The stars are relatively close together when they form but over a period of many hundreds of millions of years the stars disperse and the cluster will disappear. Our Sun would have formed in a Nebula about 4.5 billion years ago so all the Sun's siblings would have dispersed throughout the Galaxy at least 3 billion years ago. If our Open Cluster had survived until today we would have a sky full of dazzling bright stars. Every night would be as bright as our nights when there is a Full Moon and the hundreds of stars would be bright enough to cast shadows.
The names of the Seven Sisters
The Seven Sisters Cluster is close to us so the cluster has a relatively high apparent movement across the sky although it is still too slow for us to perceive. It will take 30,000 years to move a distance equal to the diameter of our Moon.
Although the cluster is moving through space the individual stars all have slightly different trajectories and relative speeds. Gradually over millions of years the stars will move further apart and the cluster will disperse, like the Hyades. Binoculars will reveal around 30 to 50 stars in the cluster and a telescope will reveal many more. However the cluster is too large to fit into the field of view of most telescopes so the outline of the cluster will be lost.
There is another very interesting object in Taurus. At the end of the lower left (eastern) arm of Taurus is Messier 1 (M1) the Crab Nebula. See the Taurus chart above. It can be seen using binoculars in a dark clear sky but really needs a telescope. From Aldebaran look east to the star ? (Ksi) Tauri. Just above ? Tauri is a small smudge of light, this is M1.
Messier 1 (M1) the Crab Nebula imaged by Hubble
This is the remnant of a giant star that exploded as a Supernova about 7000 years ago. The light from the explosion took 6000 years to reach Earth and was observed by Chinese astronomers in the year 1054 AD. It has faded now and has expanded but can still be seen in a dark clear sky as a ‘fuzzy' patch of light using a medium sized telescope.
A Supernova is the ‘death' of a star more than three times the mass of our Sun. Giant stars consume their Hydrogen fuel at an experientially faster rate than smaller stars. Consequently bigger stars do not ‘live' as long as smaller stars. As stars begin to exhaust their supply of Hydrogen they develop into a Red Giant like Aldebaran. Very massive stars develop into larger Red Super Giants.
A star like our Sun and those up to about twice the mass of our Sun become Red Giants and eventually slowly collapse as their fuel eventually runs out. The outer layers of the Red Giant drift away to form a gas bubble but the core ‘gently' collapses to form a White Dwarf Star.
Stars that are three or more times the mass of our Sun come to a more dramatic end. As the fuel of a larger Red Giant Star finally runs out the star suddenly collapses and all the mass of the star falls inwards under the massive force of its own gravity. The collapse reaches a point where the pressure and heat causes a gigantic thermonuclear explosion. The outer regions of the giant star are blown into space to create a Supernova Remnant like M1. The inner regions are compressed into a super dense Neutron Star about 10km in diameter but with a mass from 1.4 times and up to just over twice the mass of our Sun.
These tiny stars spin very fast with some spinning faster than 1000 revolutions per second. They also have powerful beams of high energy particles emanating from their poles. The axis of spin is often not at the actual pole of the Neutron Star so the beams can sweep around the sky. If one of these beams sweeps past in our direction we will see a burst of radiation mainly of short radio waves. These are seen as regular pulses at the frequency of the star's rotation. These very regular pulses lead to the discovery of these very strange stars so they are also called ‘Pulsars'.
A QUICK LOOK AT SOME TYPES OF STAR
We have examples of all the types of star mentioned in the article above on view in the sky at the moment. The bright red star Aldebaran, located at the centre of Taurus is a Red Giant about 1.16 times the mass of our Sun. So it is about the same mass as our Sun but has progressed further along its line of development (life time). It has used up most of its Hydrogen fuel and has started to fuse some of the Helium that has accumulated in its core. The additional energy from the Helium has pushed the outer layers of the star outwards. The diameter of Aldebaran is now 44 times greater than our Sun. Our Sun is 1.4 million kilometres in diameter so Aldebaran is something like 61.6 million kilometres in diameter.
Later in the night the beautiful constellation of Orion will be rising over the eastern horizon. The bright orange star at the top left of Orion is Betelgeuse a Red Super Giant. It has a mass 11.6 times that of our Sun but its diameter is about 900 times the diameter of our Sun. It will finally explode as a Supernova to produce a Supernova Remnant like Messier 1 (M1) the Crab Nebula. At the centre of the Supernova Remnant will be a Neutron Star (Pulsar) similar to the one in M1.
The star Rigel at the bottom right of Orion is a Super Giant star that is in the prime of its ‘life'. It has a mass 23 times greater than our Sun and shines about 250,000 times brighter than our Sun. It will also become a Red Super Giant and will eventually explode as a Supernova to produce a Neutron Star or perhaps even a Stellar Black Hole.
Orion's Hunting Dog ‘Canis Major' is marked by the closest and brightest star in our sky and is called Sirius. It is a star similar to our Sun but twice the mass and about 25 times brighter than our Sun. It is in fact a double star but its companion was probably a little larger than Sirius and lived its ‘life' faster. It became a Red Giant like Aldebaran then collapsed to form a white Dwarf Star. It is now about the size of our planet (12,000 km diameter) but has a mass about the same as our Sun. In the Constellation of Lyra is the bright star Vega (at the top right star of the Summer Triangle). Vega is a star similar to our Sun but about twice the mass and about 40 times more luminous. Just below Vega is Messier 57 (M57) a Planetary Nebula. A Planetary Nebula is nothing to do with a planet it is in fact the remnant of a star similar to our Sun. It has passed through its Red Giant phase and has collapsed to form a White Dwarf Star. The outer layers of the Red Giant drifted off into space as the core of the star collapsed. A beautiful ‘ring' shaped bubble was formed by the outer layers that is now called the Ring Nebula Messier 57 (M57).
We will be having a closer look at Orion next month and his Hunting Dogs in January.
THE SOLAR SYSTEM THIS MONTH
MERCURY will not be observable this month as it will be too close to the Sun as it rises in the East. However during the afternoon of Monday 11 th November there will be a Transit of the planet Mercury. Transits occur when the inner planets Mercury or Venus pass directly between the Sun and Earth. Mercury will appear as a small dot that can be seen to slowly move across the Sun. The last transit of Mercury was on Monday 9 th May 2016 and the next transit will be on 13th November 2032.
The projected image of the 7th May 2003 transit
A telescope fitted with a suitable and safe solar filter will be required to see Mercury during the transit. Alternatively the image from a telescope must be projected on to a screen for safe viewing (see the images above and below). Never look directly at the Sun and never use binoculars or a telescope to look at the Sun without a solar filter.
The telescope set up used to take the picture above.
Here are the key times for watching the transit:
Begins: Monday 11th November 2019 12:35
Midpoint: Monday 11th November 2019 15:19
Ends: Monday 11th November 2019 16:17
Duration: 3 hours, 42 minutes
The very end of the transit will not be visible from the UK as the Sun sets over the western horizon at 16:15.
Location of Mercury at 13:00 (sky darkened)
Transits of Mercury usually occur every 10 years then 3 years and then another 10 years and 3 years. The 10th year always occurs in May and the 3rd year transit is always in November. The last transit of Mercury was on the 9th May 2016 three years ago so this coming transit will be on Monday 11th November 2019. The next transit will be an odd one occurring on 13th November 2032 (13 years) then 7th November 2039 (7 years) It then reverts back to 7th May 2049 (10 years) and 8th November 2052 (3 years).
A SOHO image of the 9th May 2016 transit
Transits of Mercury are not spectacular but they are interesting because Mercury is difficult to see as it is always close to the Sun. A transit does allow us to see Mercury even though it is in silhouette. If it is cloudy or it is not possible to follow the transit, SOHO images can be obtained from NASA's Solar and Heliospheric Observatory at: http://sohowww.nascom.nasa.gov/ .
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 above the Sun) on 14th August and is now moving away from the Sun. See the charts above and below.
The Planets at Midday on 15th November
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 looked rather disappointing in the dirty and turbulent air close to the horizon. We will now have to wait until next summer to see it again.
Jupiter, Saturn and Venus at Sunset
SATURN will be in the south west as the sky darkens and is following Jupiter along the ecliptic towards the western horizon. Saturn is low and in the murky and turbulent air close to the southern horizon. It may still just be possible to see the ring system although it will appear unstable due to the air movement close to the horizon. It will require at least 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 charts above.
URANUS the Ice Giant Planet was at opposition to the Sun (due south at midnight – 24:00 GMT) on 28th October when it was 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 10th 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 GMT at the beginning of the month and at 06:35 GMT by the end of the month. It will be setting at 16:30 GMT at the beginning and 16:00 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 NOVEMBER
First Quarter will be on 4th November
Full Moon will be on 12th November
Last Quarter will be on 19th November
New Moon will be on the 26th November
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