WHAT'S UP THIS MONTH - FEBRUARY 2017

(Link to What's up - January 2017)

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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 February at 21:00 (9 o'clock) in the evening Greenwich Mean 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 in the evening sky: Uranus, Mars, Venus and Jupiter (from midnight until dawn) .

EXPLORING THE NIGHT SKY THIS MONTH

The night sky looking south on 15th February at 19:00

The chart above shows the evening sky looking south at about 7 o'clock (19:00 GMT) on 15th January. 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 constellations through which the ecliptic passes are known as the constellations of the ‘Zodiac'.

Constellations through which the ecliptic passes this month are: Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion) and Virgo (the Virgin) just appearing over the eastern horizon.

The Milky Way (our Galaxy) appears to rise up from the south eastern horizon. It continues up through the constellations of Monoceros, Orion, Gemini, Auriga, Perseus and into Cassiopeia at the top right of the chart.

Neptune is in Aquarius and now moving over the western horizon. Mars (the Red Planet) is in Pisces and is still visible in the south west in the evening twilight. Uranus is also in Pisces and still in a good position for telescopic observation. Venus is also in Pisces and rising higher in the west in the evening over the next few months. Jupiter is an early morning object rising before midnight in the east. It is very bright and easy to find in the south until the sky brightens at about 7 o'clock. Saturn is a very early morning object in the constellation of Ophiuchus but is too close to the Sun and not observable.

The beautiful constellation of Orion is now dominating the southern sky. Orion is the mythical hunter with his two hunting dogs Sirius and Procyon. It is almost due south by 20:00 but can be seen in the south east and east in the earlier evening. Orion is the main feature in the Newbury Astronomical Magazine this month.

To the north of Orion are the fairly obvious constellations of Taurus and Gemini. To the north west and sitting astride the ecliptic is the constellation of Taurus (the Bull). The Taurus asterism (shape) looks like a squashed cross ‘X'. At the centre of the cross is a large, faint Open Cluster called the Hyades. It has the bright Red Giant star Aldebaran in the centre. The real beauty of Taurus is the naked eye Open Cluster M45 the Pleiades.

To the north of M45 the Pleiades cluster in Taurus is a line of stars defining the constellation of Perseus. The whole asterism (shape) of Perseus looks like a horse rider's stirrup. At the top of the line of stars is the beautiful object ‘the Double Cluster' that is best seen using binoculars but can be seen on a clear dark night with the naked eye as a ‘fuzzy' patch of light.

Following Taurus along the ecliptic is Gemini (the Twins). The twin stars Pollux and Castor are easy to find. There is a lovely Messier Open Cluster M35 in Gemini just off the end of the line of stars emanating from the bright star Castor. Castor is a rather nice double star when viewed through a telescope.

To the east of Gemini is the faint and rather indistinct constellation of Cancer (the Crab). Even though the asterism (shape) of Cancer looks quite uninteresting it does have a very nice Open Cluster called Messier 44 (M44) Praesepe or the Beehive Cluster. M44 does look like a swarm of bees around an old style hive. It is large with dispersed stars and is best seen using binoculars.

High in the west are the conjoined constellations of Pegasus and Andromeda. Following the lower and brighter line of stars that define Andromeda, count along two stars (three including Alpheratz) to Mirach. Then count two stars up (three including Mirack) and just to the right of the second star is a small fuzzy patch of light, this is Messier 31 (M31) the Great Spiral Galaxy.

CONSTELLATION OF THE MONTH – Orion (the Hunter)

The constellation of Orion (the Hunter) photographed by Nicky Fleet

Orion is one of the easiest constellations to recognise and dominates the southern sky at this time of the year. There are many depictions of Orion shown on many different star charts. Some old pictures of Orion are very beautifully drawn in fact some are so beautiful that the artists even moved the positions of some of the stars so they would fit the image they had drawn.

Chart showing the stick figures and the illustrations superimposed

Orion the Hunter appears in the winter sky, with his club held over his head and his shield (sometimes shown as a lion's skin) held out in front of him. His hunting dogs, Canis Major (the star Sirius) and Canis Minor (the star Procyon) following behind him.

Orion is not only one of the most beautiful constellations it is also one of the most interesting with stars ranging from the very youngest to stars reaching the end of their life.

Orion is one of the few constellations that does look (with a little imagination) like what it is named after. The most obvious feature is the line of three stars, called Alnitak, Alnilam and Mintaka that make up Orion's belt. From his belt we can see two bright stars called Saiph and Rigel below. These define the bottom of his ‘skirt like' tunic.

Above the belt are two stars Betelgeuse and Bellatrix that denote the position of his shoulders. Above and between his shoulders is a little group of stars that mark out the head. From his left shoulder (Bellatrix) he holds out a shield. From his right shoulder (Betelgeuse) a club is held above his head. It almost looks as if Orion is fending off the charge of the great bull Taurus who is located above and to the west (right) of Orion.

Appearing to hang down from Orion's very distinctive belt is a line of stars, ending at the star Nair al Saif that looks very much like a sword attached to his belt. Here can be found the main interest in Orion, the Great Nebula, see the following pages for details.

Orion with his hunting dogs Sirius and procyon

If an imaginary line is traced down from the belt for about six belt length towards the south eastern horizon, a bright twinkling star will be seen. This is Sirius, Orion's Large Hunting Dog in the constellation of Canis Major. It is the brightest and closest star to be seen from the UK at just 8.6 light years from us. It is also the brightest star in the whole of the night sky. It shines with a magnitude of -1.4 and is almost pure white. Sirius is 1.8 times as massive as our Sun and 23 times brighter. To Orion's left (east) of Betelgeuse, a bright star in a rather large empty area of sky can be seen. This is Procyon in Canis Minor, Orion's Small Hunting Dog. Coincidentally both of these ‘Dog Stars' are double stars that have a small, very massive but almost invisible white dwarf companion .

When we look towards Orion we are looking into one of the nearest spiral arms of our galaxy the Milky Way. Our Sun appears to be located in the area between two spiral arms. Towards the centre of the Galaxy from our point of view is the Sagittarius Arm and looking away from the centre is the Orion Arm.

An artist impression of our position in the Galaxy

Most of the stars in Orion are located about 900 light years away from us including Rigel but Betelgeuse is much closer at only 650 light years distant. Because the stars of Orion are in a spiral arm there is a lot of gas and dust around the whole area of the constellation. Huge numbers of young bright stars are hidden by the gas and dust.

 

THE STARS OF ORION

As well as being one of the most spectacular and beautiful constellations, Orion is also very interesting because we can see evidence of all the stages of the life cycle of stars from birth to death. Obviously we can't see the life cycle of an individual star but we can observe stars at various stages of their existence in Orion.

Stars are not actually living things like us but they do exist in various stages of evolution that resemble the life cycle of living entities. We saw in the January issue of this magazine that stars are being ‘born' in the stellar nursery in Orion's sword in the Great Nebula M42. These stars are still very young and at this stage are very active. After a few tens or hundreds of millions of years they will settle down to live the longest stage of their lives as normal ‘Main Sequence' stars. Our Sun is about 4.3 billion years old and approaching half way through its main sequence. We can see many stars at this stage in Orion and others older and many much younger.

There is another factor that affects the life span of a star and that is its mass (the amount of Hydrogen gas it is made of). Large stars have denser and hotter cores and their nuclear fusion process produces more energy and consumes the Hydrogen at a much faster rate. These large stars use up the fuel supply very quickly and therefore have short lives (some less than 5 million years). There are two bright stars in Orion that demonstrate this very well. The first is Rigel at the bottom right of Orion. This is a star about 30 times the mass of our Sun and about 120,000 times more powerful than our Sun.

A star like our Sun will fuse Hydrogen into Helium and towards the end of its life will begin to fuse some of the Helium. A larger star like Rigel will be able to fuse the Helium and then manufacture other heavier atoms until Iron is produced. At this point it will have become a Red Giant and will eventually explode as a Super Nova.

Rigel as seen using a telescope

Rigel is currently a star in its prime, very powerful and mature and perhaps just moving towards the end of its middle age. Another star Betelgeuse, located at the top left of Orion is much further along its pathway of ‘life'. It is approaching the last phases of its existence as a normal star and has grown into a Red Giant with a diameter greater than the orbit of Jupiter in our Solar System.

Betelgeuse is so big and unstable that it pulsates and wobbles rather like a water filled balloon. By carefully observing the brightness of Betelgeuse it can be seen to brighten and fade. At its brightest it can be as bright as magnitude 0.2 and at its dimmest only magnitude 1.2. It is quite difficult to determine the cycle of the pulsations and brightening because there seems to be a number of intertwined cycles. So it appears to vary at different rates of between 150 to 300 days.

Betelgeuse as seen using a telescope

Betelgeuse appears to be edging towards the end of its life. In fact it is the closest star to us that might explode as a super nova at any time in the near future (astronomically speaking). It could explode and destroy itself sometime in the next million years (maybe as soon as tomorrow). For all we know it may have already exploded but the light from the explosion will take 650 years to reach us.

These two stars are close enough to us and so bright that we can even see their nature with our naked eyes. Rigel is obviously very white in appearance which is even more obvious using binoculars or a telescope. This is because it is very hot with a surface temperature of about 12,000ºK compared to our Sun at about 6400ºK. This is in contrast to Betelgeuse which is only 3500ºK and looks distinctly orange to the naked eye and again more so when viewed using binoculars or a telescope.

Betelgeuse looks red (orange) because it is more advanced in its life cycle than Rigel and has already moved into its Red Giant Phase. The nuclear fusion process is fusing the heaver atoms it has produced into even heavier elements, with each fusion stage contributing additional energy to power the star. All this additional energy pushes out against the force of gravity pushing inwards. The additional energy has forced the outer regions of the star to expand outwards to produce this huge (in volume) bloated and unstable Red Giant star.

An impression of what Betelgeuse might look like

Giant stars like Rigel and Betelgeuse destroy themselves dramatically in a massive super nova explosion but smaller stars like our Sun reach their end in a much less dramatic way. With less pressure and heat in their core they cannot fuse atoms heavier than Helium to create the heavier elements. They consume their fuel supply a lot slower and therefore last much longer. Our Sun had enough Hydrogen, when it formed, to last about 10 billion years and has so far, in the last 4.3 billion years, used just under half of its fuel.

In another 4 billion years our Sun will begin to fuse the Helium that has accumulated in its core. The additional energy produced by the fusion of the Helium will cause the Sun to inflate to become a red giant. It is thought the Sun may reach a diameter equivalent to the orbit of Earth before the fuel supplies are exhausted. The outer layers will drift away into space to create a beautiful bubble called a Planetary Nebula. As fusion, in the core, begins to break down and stop, the radiation pressure that had been overcoming the force of gravity also disappears and the star will begin to collapse inwards. It will collapse into a dense sphere called a White Dwarf about the size of Earth ~12,000 km but still weighing about the same as the Sun.

In mythology, Orion the Hunter has two hunting dogs so the constellation of Orion also has hunting dogs in the form of the stars Sirius in the constellation of Canis Major (the large dog) and Procyon in Canis Minor (the little dog). Sirius can be found by following a line down from Orion's belt and Procyon can be found to the left (east) of Orion.

The White Dwarf star Sirius B compared to Earth

Both Sirius and Procyon are double stars with their companions both being White Dwarfs. The companions must have been slightly larger than the main stars we see now when they formed and used up their fuel supply quicker. The White dwarfs are too small to see but their great mass cause the stars to appear to wobble.

An image showing Sirius B (towards the lower left)

 

 

THE GREAT ORION NEBULA - Messier 42 (M42)

Below the line of three stars of Orion's belt there is a vertical line of stars forming his sword (hanging below his belt). In the line of stars making up Orion's sword a small hazy patch can be seen using binoculars or even with just the naked eye on a clear night. The hazy patch is known as M42 (Messier 42), t he Great Orion Nebula. This Nebula is a gigantic cloud of mainly Hydrogen gas mixed with other gases and dust from which new stars are being formed. Using a pair of binoculars the nebula looks like a small fuzzy patch in the line of stars.

The Trapezium cluster superimposed on M42

When seen through a telescope the ‘fan shaped' cloud like structure can been made out. Swirls of gas and dust can be seen, some are lit up but some are dark and silhouetted against the illuminated clouds behind.

The cloud is actually illuminated by the young stars forming in it. Most of the energy illuminating this nebula comes from a group of four stars known as the Trapezium. These stars have formed from the gas and dust in the nebula; they are young, hot and very active. The Trapezium can be seen easily using a small telescope. The four stars of the Trapezium (there is a fifth fainter star) are just the brightest of what is an Open Star Cluster in the process of being created. The Orion Nebula actually contains many more very young stars that are still hidden by the gas and dust of the nebula.

Special telescopes, that can detect ultraviolet and inferred radiation, can be used to penetrate the gas and dust to see the stars forming inside the nebula. There are in fact another 300+ stars forming the new Open Cluster that are currently hidden by the gas and dust clouds.

Gravity draws the atoms of Hydrogen gas together and as the gas gets denser it pulls in even more until huge contracting spherical spheres of gas are formed. As the pressure in the core of a sphere increases the temperature rises to tens of millions of degrees and the Hydrogen atoms begin to fuse together to form an atom of Helium. In this process, known as Nuclear Fusion, a small amount of mass is lost and converted into energy in the form of Gamma and X-Rays. This heats the mass of gas and it begins to shine as a bright new star.

Much of the gas and dust of the nebula is illuminated by reflecting light from the very young stars of the Trapezium in the centre of the nebula. Some gas also produces its own light because the ultraviolet radiation energy from the powerful young stars excites the gas atoms causing them to emit light somewhat like a fluorescent light.

When a photon of ultraviolet light from the powerful young stars hits a gas atom it is absorbed and causes an electron to jump from its normal orbit to a higher orbit. After a short time the electron jumps back to its original orbit and emits the excess energy in a flash of light. The colour of this light is unique to the type of atom that has emitted it. For example Hydrogen always emits red light. The glowing Hydrogen gas can be seen in the following images.

The Orion Nebula can be seen with the naked eye from a dark location on a clear moonless night. It is easily seen using a pair of binoculars. The image below shows the sort of view seen using a pair of 8 x 50 binoculars.

Binocular view of M42 with Orion's belt at the top

A small to medium sized telescope will show a larger view and some detail in M42. Structure in the nebula can be seen with parts of the nebula illuminated and other parts appearing dark. See the images below.

The sort of view seen using a small telescope

A larger telescope will show more detail and the structure of the nebula with wisps of gas appearing. Photographic images show much more detail including colour in the clouds of gas and dust. The red in the image below is typical of the emissions from Hydrogen gas.

A photographic image of M42

The whole of the sky around Orion is full of vast Hydrogen clouds. These huge clouds called Nebulae (single Nebula) and produce some of the best astronomical images. The image below shows some of the nebula to the east of Orion's belt.

The Horse Head Nebula imaged by our own John Napper

 

THE PLANETS THIS MONTH

MERCURY is a morning object rising in the east at 07:00 and very close to the Sun. It is so close to the Sun and very low over the eastern horizon this month it will not be observable.

Chart showing Mercury and Saturn in the dawn sky

VENUS is very well positioned in the south as the Sun sets and very bright at magnitude -4.6. The telescopic view is now very good because Venus is higher in the sky and above the turbulent, dirty air close to the horizon. Venus appears as a very nice crescent and is getting noticeably bigger in diameter as it approaches Earth but the crescent will be getting narrower. The brightness will remain the same because it appears larger as it gets closer to us but the crescent also becomes narrower as less of the illuminated surface is visible to us. Consequently a Moon filter is required to reduce the dazzling effect and improve the view through a telescope. See the chart below.

Chart showing Venus, Mars, Uranus and Neptune at sunset

MARS will be in the south as the Sun is setting and the sky begins to darken. The Red Planet appears small at just 5.0 arc-seconds in diameter and is fading to magnitude +1.2. Mars is getting low in the turbulent air near the horizon and will set at 21:40. Mars is falling further behind as we on Earth move faster along our orbit inside the orbit of Mars. We will have to wait until the end of this year before we begin to catch up with Mars again and it starts to look bigger. See the Venus chart above.

JUPITER is now a good early morning object. It rises over the eastern horizon at 22:00 and will be observable before midnight towards the end of the month. To avoid losing too much sleep, Jupiter can be observed in the morning before sunrise high in the southern sky. A pair of binoculars will reveal the four brightest of Jupiter's many moons, Io, Europa, Ganymede and Callisto. A small telescope will allow the moons to be seen very clearly. Jupiter is the most detailed planet to look at using a telescope and therefore the most interesting. There is always something different to see. Even a good pair of binoculars will show the four brightest moons changing position as they orbit the giant planet.

Jupiter with its four brightest moons imaged by Steve Harris

A small telescope will show the two equatorial cloud belts and a larger telescope will reveal the other fainter belts. On a clear night a larger telescope will allow the Great Red Spot to be seen. However the spot is often difficult to make out as it is usually pink in colour rather than red. A planetarium application will help identify the moons .

Jupiter will be rising over the eastern horizon at about midnight during January and will be well placed for observing from 02:00 until about 07:00 when the sky becomes too bright. It is very easy to find because it is so bright and can be seen even in the brightening dawn sky.

Jupiter imaged by Newbury's own John Napper

SATURN will be visible towards the end of February in the brightening dawn sky close to the south eastern horizon. The ringed planet rises at about 03:30 by the end of this month, this about 2½ hours before the Sun. The view of Saturn will not be good as it is still quite close to the Sun, very low and close to the south eastern horizon in turbulent and dirty air. Saturn will remain low in the sky this year so the views will not be perfect but the rings are nearly wide open and should still look very impressive.

Jupiter and Saturn at 06:00 (6 o'clock in the morning)

URANUS will be in a good observable position this month. It will be quite high in the south as the sky darkens. It will be visible using a good pair of binoculars but a telescope at a magnification of 100x or higher will be needed to see it as a small blue/green disc. See the Venus chart.

NEPTUNE will not be visible as it will be close to the western horizon as the Sun set. It will be too small and difficult to find in the bright dusk sky. See the Venus chart.

 

THE SUN

There are still occasional sunspots to see even though the active phase of the Solar Cycle is all but over.

The Sun rises at 07:35 at the beginning of the month and at 06:50 by the end of the month. It will be setting at 16:55 at the beginning and 17:40 at 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 FEBRUARY

First Quarter will be on 4th February

Full Moon will be on 11th February

Last Quarter will be on 18th February

New Moon will be on 26th February

 

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