WHAT'S UP THIS MONTH - DECEMBER 2020

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THESE PAGES ARE INTENDED TO HELP YOU FIND YOUR WAY AROUND THE SKY

TThe chart above shows the whole night sky as it appears on 15th December at 17:00 (5 o'clock) Greenwich Mean Time (GMT). The chart is drawn for 17:00 to show the position of Jupiter and Saturn in CONJUNCTION in the South West. 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 quite easy to find. This month it is in the north. 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: Jupiter, Saturn (in CONJUNCTION), Neptune, Mars and Uranus.

 

EXPLORING THE NIGHT SKY THIS MONTH

The Southern Night Sky 15th December 2020 at 17:00 GMT

The tour of the night sky this month starts early because the beautiful planets Jupiter and Saturn are moving ever closer towards the western horizon. They will be setting over the horizon at 19:10 at the beginning of December and setting at 17:45 by the end of the month. Fortunately the sky is getting dark earlier so there is still time to see the two Gas Giants appearing very close together in their planetary conjunction. They will be at their closest on 21st December when the pair will be visible together in the field of view of telescopes using a low power eyepiece but they will be setting at 18:15 on that evening. See the details about Jupiter and Saturn in 'The Solar System This Month' below:

West is to the right and east to the left. The point in the sky directly overhead is known as the Zenith or Nadir and is shown at the centre of the chart. The curved brown line across the sky at the bottom of the chart is the Ecliptic or Zodiac. This is the imaginary line along which the Sun, Moon and the 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), Capricornus (the Goat), Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram), Taurus (the Bull), Gemini (the Twins) and Cancer (the Crab, just off the chart to 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 ( labelled in yellow print). The stunning binocular cluster M45 the Pleiades (Seven Sisters) are looking beautiful in Taurus towards the east of the Ecliptic .

The summer constellations are still prominent in the early night sky. 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 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), Perseus and Auriga (The Charioteer).

All the Superior Planets (those orbiting the Sun outside Earth's orbit) are visible in the south. Jupiter and Saturn are most prominent in the south west in the early evening. Jupiter is very bright with Saturn very close by and getting closer still until they are very close together on 21st December (their closest CONJUNCTION). The Gas Giant Planets are followed across the sky by Neptune the most distant planet then the distinctly orange and bright Mars and completing the parade of planets is Uranus. The outermost planets Uranus and Neptune do really need a good large pair of binoculars to find and a telescope to see as small blue discs.

Mars was at its closest to Earth on 13th October when it was at Opposition (in the south at midnight GMT) and at its brightest this year. It is now moving away from us and will start looking smaller.

Planets observable: Jupiter, Saturn (very early evening), Neptune, Mars, Uranus (in the evening), Venus and Mercury (in the early morning in the east before sunrise).

The Winter Solstice (Midwinter Day) will be on 21st December.

There will be a Meteor shower called the Geminid Meteor Shower with a peak of activity in the early hours of the 14th December.

 

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

With a little imagination Taurus appears to be charging Orion in the illustration. Taurus 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 between 400 million and 700 million years old. It is also quite far away from us so the stars appear quite faint but it does look lovely to see when using binoculars. 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 3.5º in diameter (about 7 Moon diameters) and well dispersed.

The Open Star Clusters Hyades and Pleiades in Taurus

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 440 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 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 disperse. 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. See the chart above.

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 five times the mass of our Sun. Giant stars consume their Hydrogen fuel at an exponentially faster rate compared to 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 five 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 powerful 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 may 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 GEMINID METEOR SHOWER

 

The Geminid Meteor Shower – showing the Radiant Point in the constellation of Gemini

In the middle of this month, around 8 th to 17th December, there will be a meteor shower known as the Geminid shower. There will be a peak in activity during the evening of the 13th and morning of 14th December. The very best time to watch for the meteors will be during the early morning hours on 14th December (at 07 :00 the shower should be at its maximum as seen from the UK ).

The new Moon will be in the west during the early evening of 13th December but it will be gone by the time any serious meteor watching has started. Conditions look very promising, weather permitting and the sky will be dark and moonless all night.

The type of meteor that occurs in showers usually originates from a comet and is much more common than the ‘Fireballs' that originate from asteroids. The Geminid shower for this reason is unusual because it is thought to originate from an asteroid known as 3200 Phaethon which is a Palladian asteroid with a " rock comet " orbit. This would make the Geminids, together with the Quadrantids , the only major meteor showers not originating from a comet .

This means that some of the meteoroids (the particles moving through space) may be of a rocky nature so they will often be bright and survive for quite a long time. When they enter Earth's atmosphere about 100km up they might produce a bright and persistent trail.

The Geminid meteors also enter the atmosphere comparatively slowly at about 35 km/second compared with other showers that enter at over 75 km/second. As a result of this slower entry and some having a more robust make up, the Geminid meteors may appear brighter and their trails across the sky last longer.

The actual peek of activity will occur at 13:00 on 14th December but will not be visible from the UK as we will be in daylight. Observers in the USA will be luckier as they will be able to see it in their darkness before dawn.

Because the constellation of Gemini is above the horizon from early evening, the meteors can be seen for most of the night and in almost any part of the sky. By midnight the constellation will be almost due south and high in the sky. If you are intending to have a look remember to wrap up warm before you go out because you will soon feel very cold and that will spoil your enjoyment of the shower. Make yourself comfortable in a garden chair and spend at least an hour looking .

 

Geminid meteor shower composite by Clint Spencer

Make sure you are dressed warmly with a hat and gloves and sitting comfortably. A garden lounger chair will allow the observer to lay back and have their head supported to avoid getting a neck ache from looking up. Position the chair to face towards the south and look anywhere between south east to south west and from the Horizon to the Zenith (the point directly overhead).

ABOUT METEORS

On any clear night if you sit back and look up into the night sky for a while you will more than likely see a streak of light speed across the sky - this will be a METEOR or shooting star. It is not a star at all it is just a small speck of dust known as a METEOROID entering the Earth's atmosphere at very high speed.

This is like when the space shuttle or other space craft become very hot as they re-enter the atmosphere at about 30 thousand km/h . However these dust particles get even hotter at their re-entry speed of up to 270 thousand km/h. At this speed the dust is vaporised by the heat created by the friction with the upper atmosphere at an altitude of about 80km. T he surrounding air is also heated until it glows in a similar way to a fluorescent light.

There are two types of Meteor, the first is thought to originate from the large lumps of rock and iron left over when the planets formed , known as ASTEROIDS. Most asteroids orbit the Sun in a belt between Mars and Jupiter. The huge gravitational forces exerted by Jupiter may have pulled the rocks apart before they could accumulate into a nother planet.

Very rarely two asteroids may randomly collide but when they do, chips of rock and Iron are thrown off and occasionally may be sent spiralling in towards the Sun and Earth. These can be a few millimetres across or up to tens or even hundreds of metres across. They are quite rare and are seen as individual ‘fireballs' . Large ones can sometimes impact the ground as METEORITES and may even cause craters but these are very rare .

The second type of meteor originates from a comet and is much more common. Comets are large lumps of ice, typically between five and thirty kilometres across. They orbit the Sun in an area beyond the orbits of the outer planets called the Kuiper Belt. There are thought to be millions of these objects just sitting there quietly orbiting around the Sun at enormous distances.

Occasionally two of these lumps of ice may have a close encounter and their gravity can slightly perturb their orbits. This may move the objects enough that one might change its orbit so that will spiral in for a close encounter with the Sun. As this object, that can be thought of as a very large and dirty snowball, approaches the Sun the ice begins to melt. In the vacuum of space the frozen water will turn directly into water vapour and not pass through the liquid phase. This is called subliming.

As the ice melts the water vapour forms a cloud (called a Coma) around the solid object that is called the Nucleus. The Solar Wind (radiation from the Sun) drives the water vapour and other gases away from the coma and the familiar tail of the Comet is formed. Dust particles are released from the melting ice and slowly leave a trail along the path of the Comet as it loops around the Sun.

Comets mainly move around the Sun in very elliptical orbits that may take them out beyond the outer planets into long orbits. Some comets may have orbits taking a few decades to complete but others may take thousands of years. Every time they visit the inner Solar System they leave a dust trail along their orbit. Eventually this trail may become a ring of dust around the Sun.

This ring is tilted compared to the orbit of the planets around the Sun. Some of the dust trails spread across the orbit of Earth so once, or sometimes twice, a year Earth will pass through the dust trail. When Earth, travelling at ~108,000km/h crashes into these dust particles (that may also be travelling at a similar speed towards Earth) the combined speed of up to 270,000km/h produces a huge amount of energy. This energy is converted into heat by the friction of the dust particle with the upper atmosphere and the streak of light we call a Meteor is produced. This is the kind of meteor seen in the Geminid Shower.

 

THE SOLAR SYSTEM - DECEMBER 2020

The morning sky at 07:00 showing the positions Mercury and Venus

MERCURY will not be visible this month as it will be too close to the Sun in the east this month. See the chart above (the sky has been darkened to allow the planets to be seen). Mercury will be in Superior Conjunction (passing behind the Sun) on 20th December.

VENUS reached its greatest western elongation (at its furthest apparent distance from the Sun) on 14th August. It is still rising in the in the east before the Sun. It is now ‘gibbous' (wider than half Moon shaped see below).

It is moving back towards the Sun and will appear smaller but ‘fuller' as it moves into Superior Conjunction (behind the Sun) on 25th March 2021. After passing through Superior Conjunction Venus will reappear in the evening sky in the west as the Sun is setting.

Venus appearing ‘Gibbous' during December

After conjunction Venus will first appear close to the Sun looking small and round when viewed using a telescope. As it will be located on the other side of the Sun it will fully illuminated but will become larger and crescent shaped as it moves out from the Sun and towards us.

MARS rises in the east at midday and is still looking quite large at about 12 arc-seconds. Earth caught up and passed Mars on their orbits around the Sun. This was because Earth's orbit is inside the orbit of Mars and is consequently travelling faster. Earth overtook Mars on 13th October and this is called Opposition. At opposition Mars was in direct line with Earth and the Sun and appeared at its largest and was 17.5 arc-seconds.

At opposition Mars was at it its closest point to Earth but is still in a good position for observing in the south all evening. It will be around until May but will be moving closer to the south western horizon. It will also be reducing in size as it moves quickly away from us. After it has moved over the horizon we will not see it again for two years.

Mars, Uranus and Neptune in the evening sky

Jupiter, Saturn, Mars, Uranus and Neptune early evening on 15th December

The chart above shows the positions of the Gas Giant Planets in the middle of this month, low in the west in the early night sky after sunset. Jupiter and Saturn are moving closer together in the Conjunction (close together in the sky). They will be at their closest on 21st December.

JUPITER is now way past its best and visible in the West just after sunset. It will be difficult to see in the bright twilight sky just above the South West horizon. It will be in the thick, murky, turbulent air close to the horizon so the view will be badly distorted so very little detail will be seen. However it will be well worth searching out to see the close conjunction with fellow Gas Giant Saturn. Jupiter and Saturn will be moving closer together during December but will be at their closest point of the conjunction on 21st December.

SATURN will be very difficult to see in the bright twilight sky just above the South West horizon. See the charts below. It will be worth going to a high location (on top of a hill) with a clear view to the South West to see Saturn in conjunction with Jupiter before they disappear over the horizon.

The two Gas Giant Planets have appeared close together in the sky all summer and will continue to move even closer together until the end of the year. The converging orbital paths of the planets are shown on the chart below.

This interesting event, involving Jupiter and Saturn, will develop and become even more interesting through the months from now until the end of this year. Jupiter and Saturn are located close together in the sky at the moment and this is what astronomers call a ‘Conjunction'. This is a term used when two (or more) objects appear to move close together in the sky.

Orbital paths of Jupiter and Saturn 21st December

The orbital paths of the planets are show as red for Jupiter and brown for Saturn. It can be seen on the chart above that the orbital paths a getting closer towards the end of the year as the planets move further west.

Unfortunately Jupiter and Saturn have been low in the southern sky this year and not in a good position for observing. They have been in the thick and turbulent air close to the southern horizon so it has been difficult to see the surface details.

However the Planetary Conjunction next month should make up for the disappointing views of the planets. A clear view to the western horizon will be required to see the conjunction and the early evening sky will be bright just after the Sun has set.

Jupiter and Saturn will not be any closer to each other than they normally are and will still be moving around their established orbits. This conjunction is just a ‘line of sight' effect from our point of view on Earth. The two planets will actually be as far apart from each other as Earth is from Jupiter (about 750 million kilometres).

Jupiter is approaching Saturn as it is moving faster than Saturn along its orbital path and will overtake Saturn on 21st December. From our point of view they will appear very close together so at this time the two planets will be at their closest conjunction.

Jupiter and Saturn at their closest conjunction

The chart above shows how the two planets and their moons will appear using a telescope on the 21st December. They should fit into the field of view of most small telescopes and some larger telescopes using a low power eyepiece. Like all astronomical events the weather will need to be kind to us and we will need a clear view towards the western horizon. The conjunction will unfortunately also be in the still bright sky after sunset.

Jupiter, Saturn, Mars, Uranus and Neptune early evening on 15th December

URANUS will not be easy to see as it will be close to the southern horizon. It will rise at about 15:30 and be visible for the rest of the night. Uranus was at opposition on the 31st October. This month it will be due south and at its best at 22:40 but will need a telescope to see it.

NEPTUNE will rise at about 14:00 but will not be easy to observe this month it will be due south at about 19:30. It does require a medium sized telescope to see well.

 

THE SUN THIS MONTH

The Sun rises at about 07:50 at the beginning of the month and 08:00 at the end. It sets at 16:00 at the beginning of the month and 16:00 at the end.

Our planet Earth has its axis of rotation tilted over at 23.4º compared to the Axis of the Sun and the axis of the orbits of all the planets. This causes Earth to have Seasons as it moves around its orbit around the Sun (our year). As Earth's axis of rotation always points to the same point in the sky as it orbits the Sun we get the impression that we (from our view point on Earth) appear move higher and lower compared to the Sun. So the Sun appears to move higher in the sky in summer and lower in the winter. We will pass through the point when the Sun appears at its lowest point in the winter sky (midwinter) on 21st December, we call this the Winter Solstice.

Diagram showing how Earth's Axis of Rotation always points to the same position in the sky

The Winter Solstice (Midwinter Day) will occur on 21st December but actually occurs at 10:00 on that day this year. What this means is the Ecliptic (the position where the Sun appears move across the sky) moves south for the northern winter and north for the northern summer. The furthest position that the Ecliptic moves to the north is called the Tropic of Cancer. This will be our Summer Solstice (Midsummer Day). The furthest south that it reaches is called the Tropic of Capricorn and will be our Winter Solstice (Midwinter Day). So the Sun will be at its lowest point in the sky on 21st December and it will be our Winter Solstice so it will be our shortest day. See the diagrams above and below.

The Geographical Equator and the Tropics of Cancer and Capricorn

At the halfway point between summer and winter (when the Ecliptic is overhead on the Earth's Geoglogical Equator) it is called the Autumn Equinox (when the Ecliptic is moving south) or the Spring Equinox (when the Ecliptic is moving north).

The Ecliptic is the imaginary line that represents the equator of the Solar System and it appears to be tilted at 23.4º to us due to the tilt of our planet. The Sun, Moon and planets appear to move along this imaginary line as Earth moves around its orbit about the Sun. As the tilt of Earth's axis always points to the same direction and the same point in the sky the Ecliptic appears to rise and fall from our point of view creating our seasons.

In the northern hemisphere the North Pole of Earth's axis is tilted towards the Sun during the summer season. This gives the effect of a point on the surface (such as the UK) being closer to the equator of the Solar System (the Ecliptic). As a consequence the Sun will appear much higher in the sky during the summer. It is also warmer because the Sun is closer to overhead overhead (the Zenith).

As Earth rotates on its axis once every 24 hours (1 day) that point on the surface of Earth (the UK) will rise up due to the tilt and the Sun appears high in the sky. At midnight when the UK is looking directly away from the Sun the Ecliptic will be at its lowest point in the sky. The Moon and the planets will also appear low in the night sky.

Midwinter day at midday
Midwinter night at midnight

During the winter days the Sun appears low in the sky but at night the Ecliptic appears very high in the sky. See the charts above. This means the Moon and planets appear high in the sky as they move along the Ecliptic. In the northern hemisphere the North Pole of Earth's axis is tilted away from the Sun during the winter season. This gives the effect of a point on the surface such as the UK being further away from the equator of the Solar System (the Ecliptic) during the day and closer to the North Pole of the axis of the Solar System so the days are shorter and colder.

As Earth rotates on its axis once every 24 hours (1 day) that point on the surface of Earth (the UK) will move down due to the tilt of the axis. At midnight when the UK is looking away from the Sun it will be at its lowest point and the Ecliptic will appear high in the sky. The winter is the best time for astronomers because the nights are long and the planets and Moon are high in the sky away from the thick and turbulent air close to the horizon

 

OBSERVING THE SUN (SAFELY)

A group of Sunspots seen on 26th November

A small Sunspot was visible during the middle of October and was followed by a nice group that was seen on 7th November. Another lovely Sun Spot Group was imaged by the Solar and Heliospheric Observatory (SOHO) on 26th November, shown above and below. These mayhave been the first sunspots as we move into the ‘build up' to the next maximum of the Sun's 11 year cycle of increased activity. The Sun has been passing through its period of low activity over the last year or two and the previous Maximum was rather sparse and disappointing.

Sunspots are caused by the strong magnetic field of the Sun. We can think of the Sun being like a gigantic magnet with lines of magnetic force linking the North Pole to the South Pole. However the Sun is not solid as it is mainly comprised of Hydrogen gas and is fluid.

The equatorial region actually rotates faster than the Polar Regions. Consequentially the lines of magnetic force are dragged out and distorted around the equator. Over a period of about five years the lines of magnetic force are pulled so far around the equator they become tangled and begin to break up.

Where the lines of magnetic force interact with the surface of the Sun a cavity is created where a lower and cooler layer is exposed. As this lower layer is cooler it is less bright and appears darker hence the Sun Spot. Sunspots have a darker central area called to 'Umbra' and a lighter outer area called the 'Penumbra'.

The group of sunspots shown above enlarged

This build-up of magnetic forces has a cycle of about 11 years so we see increased and decreased solar activity over periods of about 5½ years. We are just beginning Solar Activity Cycle 25 with an increase in activity so we should start to see more Sunspots.

The previous Solar Cycle 24 had its maximum peak of activity during the summer of 2014 and the cycle was declared to be over in December 2019. The official beginning of Solar Cycle 25 has been agreed by scientists who have been closely monitoring the Sun. One of the signs is the positioning of solar magnetic activity on and below the visible surface of the Sun. This magnetic activity moves away from the equator and closer to the poles then back again over the course of a Solar Cycle, about 11 years.

Sunspots can be observed even without a telescope. Any activity can be followed by downloading the day to day detailed images of the Sun from the SOHO website at: http://sohowww.nascom.nasa.gov/ .

For those who are fortunate to have a telescope, Sunspots can be projected on to a small card screen and observed safely. Even better, a modestly priced special solar filter can be bought ready to fit and used to observe the Sun directly. These can be fitted over the end of the telescope or inside the Dew Shield. See the picture below.

The author's small Telescope fitted with a Solar Filter inside the Dew Shield

. WARNING! Never look directly at the Sun only look at the Sun using a proper safe solar filter

Looking directly at the Sun can cause blindness

 

THE MOON PHASES DURING DECEMBER

Last Quarter will be on 8th December

New Moon will be on 14th December

First Quarter will be on 22nd Dec ember

Full Moon will be on 30th December

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