WHAT'S UP THIS MONTH - FEBRUARY 2020
(Link to What's Up January 2020)
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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 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: Uranus and Venus are observable in the early evening with Mars and Jupiter in the very early morning.
EXPLORING THE NIGHT SKY THIS MONTH
The Southern Night Sky during February 2020 at 21:00 GMT
The chart above shows the night sky looking south at about 20:00 GMT on 15th February. 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 Aquarius (the Water Carrier) just moving over the western horizon, Pisces (the Fishes), Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion) and Virgo (the Virgin) rising over the eastern horizon.
Just disappearing over the south western horizon is the constellation of Aquarius (the Water Carrier) followed by Pisces (the Fishes). The planet Uranus is in Pisces and can be found in the early evening using binoculars.
Now prominent in the south is the constellation of Taurus (the Bull). It sits on the Ecliptic and looks like a squashed cross ‘X'. The most obvious star in Taurus is the lovely Red Giant Star called Aldebaran. It appears slightly orange to 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 ‘naked eye' Open Star Cluster Messier 45 (M45) known as the Pleiades (or the Seven Sisters). It really does look magnificent using binoculars.
Following Taurus along the Ecliptic is the constellation of Gemini (the Twins). The two brightest stars in Gemini are Castor and Pollux that are named after mythological twins and they are so alike they do look like twins. There are lines of fainter stars linked to Pollux and Castor and extending to the south west (down to the right). There is a lovely Open Cluster called Messier 35 (M35) just off the end and above the upper line of stars emanating from the star Castor. M35 will need a telescope to see well.
Following Taurus along the Ecliptic is the rather faint constellation of Cancer (the Crab). It does need a dark and unpolluted sky to see with the naked eye. In a good sky the faint stars can be seen and a nice Open Cluster of stars at its centre. The cluster is called Messier 44 (M44) or ‘the Beehive Cluster' because of its resemblance to an old straw built beehive with a swarm of stars looking like bees around it. It looks best using binoculars.
Following Cancer along the Ecliptic is the constellation of Leo (the Lion). It does actually look a little like a resting male African lion but perhaps more like the Sphinx in Egypt. Below Leo are some relatively bright galaxies M65, M66, M95 and M96 but they do need a telescope to see them. The sky around Leo and particularly between Leo and Virgo hosts a cluster of nearby galaxies. Our Galaxy (the Milky Way) is actually a member of a small local group of galaxies that forms part of this larger cluster of galaxies.
To the south of Taurus and Gemini is the spectacular constellation of Orion (the Hunter). Orion dominates the southern sky and is one of the best known constellations and hosts some of the most interesting objects for us to seek out. See the January What's Up (Click on the link at the top of this page).
CONSTELLATION OF THE MONTH - TAURUS
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 and the surrounding constellations
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. An Open cluster is created as stars form in a giant cloud of gas and dust called a ‘Nebula'.
M45 is visible to the naked eye initially looking like a ‘fuzzy' patch of light. Closer observation 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. 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 exponentially 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 20km 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'.
THE SOLAR SYSTEM THIS MONTH
MERCURY will be observable this month in the west as soon as the Sun sets. The innermost planet will be at Greatest Eastern Elongation (furthest position from the Sun, see the red orbit below) on 10th February. Mercury is small but quite bright although its brightness is rather overwhelmed by the brightness in the sky from the setting Sun. It is best seen using binoculars but we must wait until the Sun has disappeared over the horizon before sweeping the sky using binoculars to find Mercury.
Mercury, Venus, Uranus and Neptune at sunset
VENUS has been moving out from behind the Sun. See the gray orbit arc on the chart above. The fainter section (below the elliptic) shows the section Venus has moved along and the brighter section is the part of its orbit it will be moving along during the next few months. So Venus is looping out from behind the Sun and moving towards us. It will soon appear to be moving back towards the Sun, following the brighter gray orbit arc. Venus will become a narrower crescent shape but will appear to become larger in diameter as it moves closer to us.
Venus how it will appear on 15th February
MARS will be observable (with difficulty) this month low in the east before sunrise. Mars is still a long way from us on the other side of the Solar System so it looks small at just 5.1” (arc seconds). See the chart below.
JUPITER is moving away from the Sun in the early morning sky in the east. It will be very low in the sky and looking rather disappointing in the dirty and turbulent air close to the horizon. See the chart below
SATURN will be low in the south east as the sky brightens and the Sun rises over the eastern horizon. Saturn is very low and in the murky and turbulent air close to the southern horizon. It will be in the bright dawn sky and will require a clear view to the eastern 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. See the chart below.
Mars, Saturn, Jupiter at Sunrise on 15th February
URANUS will be visible during 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 Mercury chart above.
NEPTUNE is now moving towards the western horizon. 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 Mercury chart above.
There was one small sunspot visible at the end of January even though we are in the inactive phase of the Solar Cycle. No other sun spots have been seen since early last year and that was just one fairly large one. See the image below:
The sunspot imaged by SOHO on 29th January 2020
The Sun rises at 07:30 GMT at the beginning of the month and at 06:50 GMT by the end of the month. It will be setting at 16:50 GMT at the beginning and 17:35 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 FEBRUARY
First Quarter will be on 2nd February
Full Moon will be on 9th February
Last Quarter will be on 15th February
New Moon will be on the 23rd February
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