WHAT'S UP THIS MONTH - AUGUST 2020
(Link to What's Up July 2020)
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THESE PAGES ARE INTENDED TO HELP YOU FIND YOUR WAY AROUND THE SKY
The chart above shows the whole night sky as it appears on 15th August at 22:00 (10 o'clock) in the British Summer Time (BST). As the Earth orbits the Sun and we look out into space each night the stars will appear to have moved across the sky by a small amount. Every month Earth moves one twelfth of its circuit around the Sun, this amounts to 30 degrees each month. There are about 30 days in each month so each night the stars appear to move about 1 degree. The sky will therefore appear the same as shown on the chart above at 11 o'clock BST at the beginning of the month and at 9 o'clock BST at the end of the month. The stars also appear to move 15º (360º divided by 24) each hour from east to west, due to the Earth rotating once every 24 hours.
The centre of the chart will be the position in the sky directly overhead, called the Zenith. First we need to find some familiar objects so we can get our bearings. The Pole Star Polaris can be easily found by first finding the familiar shape of the Great Bear ‘Ursa Major' that is also sometimes called the Plough or even the Big Dipper by the Americans. Ursa Major is visible throughout the year from Britain and is always quite easy to find. This month it is high in the west. Look for the distinctive saucepan shape, four stars forming the bowl and three stars forming the handle. Follow an imaginary line, up from the two stars in the bowl furthest from the handle. These will point the way to Polaris which will be to the north of overhead at about 50º above the northern horizon. Polaris is the only moderately bright star in a fairly empty patch of sky. When you have found Polaris turn completely around and you will be facing south. To use this chart, position yourself looking south and hold the chart above your eyes.
Planets observable: Jupiter, Saturn, Neptune, Mars, Uranus (in the evening) and Venus (in the early morning).
EXPLORING THE NIGHT SKY THIS MONTH
The Southern Night Sky 14th July 2020 at 01:00 BST
The chart above shows the sky as it will appear at midnight on 15th August to show the positions of all the outer planets. Across the lower part of the chart is the brown curved line depicting the Ecliptic also called the Zodiac. This is the imaginary line along which the Sun, Moon and planets appear to move across the night sky. It is actually the equator of the Solar System and the plane of the orbits of the planets including Earth. The Ecliptic is low at this time of the year due to Earth's 23.4º tilted axis of rotation. So we see the Moon and planets low in the night sky and the Sun high in the midsummer sky during the day.
All the Superior Planets (outside the orbit of Earth) are visible this month. Venus will be visible in the east before sunrise.
Constellations through which the ecliptic passes this month are: Virgo (the Virgin), Libra (the Scales), Scorpius (the Scorpion). These constellations will have set over the western horizon by midnight. The following constellations can be seen during the night: Sagittarius (Archer), Capricornus (the Goat), Pisces (the Fishes) and Aries (the Ram).
All the stars in the night sky appear to rotate around a point in the sky that we call the ‘North Celestial Pole'. This point is located very close to the star Polaris in the constellation of Ursa Minor (the Little Bear) which is partly visible at the top of the chart.
Polaris can always be found by first finding Ursa Major and following the two ‘pointer' stars opposite the handle of the ‘saucepan shape', up out of the pan. This line points to Polaris about five times the distance between the two pointer stars in Ursa Major.
Our planet Earth rotates around the North Celestial Pole (Polaris) once every day (24 hours). As Earth rotates, the sky appears to rotate above us. As the sky appears to rotate, Ursa Major and the other constellations will appear to move around the North Celestial Pole in an east to west direction. The whole sky will appear to move anticlockwise around Polaris. The movement is slow and not perceivable in real time. The whole sky also appears to move east to west by approximately 1º per day due to Earth's orbit around the Sun every 365.25 days.
The summer sky is dominated by the ‘Summer Triangle' first identified by Sir Patrick Moore. The corners of the triangle are marked by the stars Deneb in Cygnus, Vega in Lyra and Altair in Aquila.
Albirio in Cygnus can be seen as a beautiful double star when viewed through a telescope. One star is bright and gold in colour the other is fainter and distinctly blue. This is not a true pair they just happen to be in the same line of sight. Although the blue star is much bigger and brighter than the golden coloured star it is a lot further away from us.
The constellation of Lyra (the Harp) is located to the west (right) of Cygnus but is much smaller. The most obvious feature of Lyra is the very bright star Vega that is located the top right corner of the Summer Triangle. Vega is the fifth brightest star in our sky with a magnitude of +0.4. It is located at a distance of 25.3 light years from us and is thought to be 3.2 times the diameter of our Sun and 58 times brighter. The main asterism (shape) of Lyra is composed of a line of three stars with Vega in the centre and a group of four fainter stars that form a parallelogram shape that is known as the ‘Lozenge'.
Between the two lower stars: Sulafat and Sheliak is the Messier object M57 also known as the Ring Nebula. This is a ‘Planetary Nebula' which has nothing to do with a planet. It is in fact a dying star that was similar to our Sun but older. The star had used most of its Hydrogen fuel and expanded to form into a Red Giant.
After passing though that red giant phase it gently collapsed to become a White Dwarf. The very thin outer mantle of the red giant drifted away into space as the star collapsed. The white dwarf is now surrounded by a bubble of gas and dust. It looks like a small ‘smoke ring' when seen through a telescope but can't be seen using binoculars.
What we are seeing in M57 is what the last gasps of our Sun will be at the end of its existence as a normal star in about five billion years time .
Planets observable: Jupiter, Saturn, Neptune, Mars, Uranus (in the evening) and Venus (in the early morning).
COMET 2020 F2 (NEOWISE) OBSERVED LAST MONTH
Comet 2020 F3 imaged by Steve Knight
Comet 2020 F3 (NEOWISE) has graced the night sky since early July and is now moving away and will not return for over 6000 years. It is fair to say that this comet has exceeded expectations after so many recent disappointments. It has reach naked eye visibility even in light polluted areas such as Thatcham.
The comet imaged by Emma Chivers Thatcham
The image above was taken by Emma using just her mobile phone camera through the window in her roof on 16th July. Look just to the right of the tree and above the street lights. The comet actually looked larger and brighter than the image shows it.
The comet has been close to the northern horizon and has therefore needed a clear view to north. The bright star Capella in the constellation of Auriga has been a useful guide to help with locating NEOWISE (see Emma's picture, Capella is on the right edge half way up).
In a darker sky the comet has been easy to spot and well within ‘Naked Eye' capability. It reached Perihelion (closest approach to the Sun) on 3rd July. It stayed at naked eye brightness until its closest approach to Earth on 23rd July. It had reached a magnitude of around +3 and was even visible in light polluted areas but perhaps requiring binoculars in the more light polluted areas.
The image below was taken using a DSLR camera mounted on a tripod and set to manual operation. So the focus was set manually and the exposure set to 25 seconds and making sure the flash was turned off. It took some trial and error to get the image right but a reasonable result was achieved in the end.
Comet 2020 F3 imaged by Steve Harris 17th July
The bright coma is well defined in the image as was described by other observers. The location was in a ‘pull in' by the roadside on Burys Bank at Greenham Common looking over Thatcham to the north.
The image below was taken by Steve Knight at 23.50 on 20th July. Two tails can be seen on the image. The brighter curved tail on right is dust tail and the one on left is the blue ion tail.
Comet 2020 F3 imaged by Steve Knight
The image was produced using 36x 10sec exposures from a Sony A7S camera with a 135mm f2 lens on Astrotrac and was set at ISO 6400. The 36 images were stacked in DSS and processed in Pixinsight and Faststone Image Viewer
THE CONSTELLATION OF PERSEUS
The Constellation of Perseus
Perseus is our constellation of special interest this month because it is host to the Radiant of the Perseid Meteor shower. The other articles in the magazine this month give the details of the meteor shown but the constellation of Perseus has interesting things to see as well.
The asterism (stick figure shape) looks rather like a horse riding stirrup. The two brightest stars Algol and Mirfak along with the fainter star Atik mark out the ‘V' main shape with another line of stars pointing from Mirfak towards the very obvious ‘W' shape of Cassiopeia.
Other constellations around Perseus are: Cassiopeia to the north, Andromeda to the west (right) Auriga to the east (left) and Taurus to the south (below). Continuing along the line of stars from Mirfak to Atik is the beautiful Open Cluster of stars Messier 45 (M45) the 'Pleiades' also called the Seven Sisters can be found in the constellation of Taurus (the Bull).
During the summer months Perseus is located in the north close the horizon so that is where it can be found this month. During the winter it is located almost overhead and during November and December is actually host to the Zenith (the point in the sky directly over head).
The constellation of Perseus is also host to one of the best annual meteor showers which is called the Perseid Meteor Shower. The meteor shower is named after Perseus because the meteors of this shower appear to radiate out from a point located in Perseus. This Radiant is actually located very close to the point on the chart above marking the two NGC objects NGC884 and NGC869. So the Radiant has been omitted from this chart but can be seen in detail in the article about the Perseid Meteor shower below.
Details of NGC884 and NGC869 are also shown below.
Perseus is host to two Messier ‘deep sky' objects Messier 34 (M34) and Messier 76 (M76). M76 is a rather nice Planetary Nebula which is sometimes called the Little Dumbbell. This is a star similar to our Sun that has collapsed to become a White Dwarf and has developed a ‘bubble' of gas around it. It does need a medium sized telescope to see it.
Messier 34 is a fairly bright Open Cluster comprised of about 80 stars. It can be seen as a small ‘fuzzy' patch of light using binoculars but does need a telescope to see as a cluster of stars.
Messier 34 (M34) Open Cluster
Messier 76 (M76) Planetary Nebula
However there is another Open Cluster or rather two clusters called the Double Cluster that is listed in the New General Catalogue as NGC 869 and NGC 884 and shown in the image below.
NGC 869 and NGC 884 the Double Cluster
The Double Cluster can be seen on a clear dark night with the ‘Naked Eye' as a ‘fuzzy patch of light in the line of stars leading from the star Mirfak up towards the constellation of Cassiopeia. It is best seen using binoculars or a small telescope fitted with a low power eyepiece (25mm or 32mm). It is not clear whether this is a true associated double cluster or just a ‘line of sight' coincidence.
THE PERSEID METEOR SHOWER
The Perseid Meteor Radiant at 01:00 14th August looking north
Meteor showers are notoriously unpredictable. The exact time of any spectacular increase in numbers or if the meteors will be bright is difficult to predict as is the clear weather needed to see them. However every year on the evenings of the 11th and 12th August there is usually a spectacular display from the Perseid Meteor Shower.
Unfortunately this year there will be a bright Last Quarter Moon rising in the east on the 12th August so some of the fainter meteors may be drowned out. The meteors of a shower appear to radiate from a point in the sky that is called the ‘Radiant'. The meteors of this particular shower appear to originate from a ‘Radiant' point in the constellation of Perseus. See the chart above and the images in the next section.
If the trail of any meteor that is seen can be tracked back and found to have originated from this radiant point it will be a Perseid. A few meteors might appear to originate from other directions so these are the meteors that might be seen randomly and not part of any named shower. These are known as Sporadic Meteors.
From a clear dark site, the constellation of Perseus can be clearly seen as a line of stars stretching from the very distinctive ‘W' shape of Cassiopeia towards the northern eastern horizon. The brighter stars appear to mark out the rough shape of a horse riding spur.
If the sky is clear the Milky Way (our galaxy) can be seen rising up from the northern horizon passing through Perseus, Cassiopeia and right across the sky though Cygnus and the Summer Triangle. The bright star Capella in the constellation Auriga will be twinkling noticeably close to the northern horizon. See the chart on page 1.
No special equipment is required to see meteors but it does pay to make yourself comfortable for a meteor watch. It is essential to dress to keep warm. A warm coat should be worn along with a good thick pair of trousers or perhaps an extra pair of trousers or long legged underwear can be worn for additional comfort. It can get very cold during the night even during the summer.
A garden lounger will make the observer much more comfortable and avoid getting a stiff neck from looking up for too long. It will also allow an extra blanket to be used if it is chilly.
Observing can start as soon as it is dark but there is likely to be more meteors after midnight. Position the lounger so your feet point towards the northern horizon. Look at about 45º above the horizon and anywhere between west, through north and to the east so more or less anywhere in the northern hemisphere of the sky. Meteors will appear as a fast streak of light flashing across the sky. One or two bright meteors every five to ten minutes may be seen.
Some might be fainter and difficult to see from a well-lit area in the towns. Any bright meteors will be seen even from fairly light polluted skies. These may appear anywhere in the sky from close to the radiant point in the north to directly overhead. With a clear sky it may be possible to follow the tracks back through the constellations they passed through to the radiant point in Perseus. See the images in the next section.
WHAT IS A METEOR?
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 just like how a space craft become very hot as it re-enter s 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 and the surrounding air is also heated until it glows in a similar way to a fluorescent light.
As Earth is travelling at about 100,000 km/h around the Sun the meteors appear to radiate from a point in the direction we are travelling. This is rather like driving a car into a snow storm as shown below where the flakes appear to radiate from a point directly ahead.
Driving into a snowstorm
A meteor shower radiant
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 planet.
Very rarely two asteroids may collide but when they do, chips of rock and Iron are thrown off and occasionally may head towards 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.
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 that reside beyond the orbits of the outer planets. There are millions of these objects just sitting there quietly orbiting around the Sun at enormous distances.
Occasionally one of these objects may be nudged out of its orbit by a close encounter with another object and may begin to move in towards the Sun. A comet can be thought of as being like a giant dirty snowball. As it approaches the Sun, the water and frozen gases begin to boil off by the radiation from the Sun. The gases are ionised by the Sun and form a blue tail and dust will form a curved white tail to create the familiar twin tails associate with many comets.
Comet Hale Bopp seen in 1998
Dust particles released by the melt are heavier and therefore continue more or less on the same orbit. Some comets return in periods of tens or hundreds of years so particles become spread out along the orbital path and may eventually form a complete ring around the orbit.
Once or twice a year Earth may pass through this stream of particles that then collide with the atmosphere as Meteors. Meteoroid dust particles are usually small and very light and generally have the consistency of cigarette ash.
The clarity of the sky will make a significant difference to the number of meteors that can be seen. Any mist or hazy cloud will severely reduce the chance of seeing the fainter meteors especially if observing from a light polluted area. If it is cloudy there is of course less chance of seeing any meteors at all. It is never possible to predict exactly when the maximum peak might appear and sometimes it may not appear at all. This it because the dust from the comet that produces the meteors moves through space in wisps and filaments. All depends on whether Earth passes through a filament and how thick that filament is.
Meteoroid path showing wisps and filaments
Travelling at between 11 and 76 km per second meteors have a lot of kinetic energy (energy due to velocity) and burn up in the atmosphere at a height of about 100 km. Only the largest rocky or metal meteors from asteroids reach the ground. So nearly all the meteors originating from comets burn up in the upper atmosphere and present no danger to us.
The only thing that is predictable about meteor showers is they will always be unpredictable. Just hope for a clear sky and a good shower.
THE SOLAR SYSTEM THIS MONTH
The night sky at midnight showing the positions of all five of the outer planets
MERCURY will not be visible this month as it is in the bright sky before sunrise on the north eastern horizon. See the chart below.
Mercury and Venus at sunrise on 15th August
VENUS will be observable in the east before sunrise. It rises over the eastern horizon at 02:00 so will be observable from 03:00 until sunrise. Venus will appear ‘half Moon' shaped as it will be at greatest western elongation (at its furthest apparent distance from the Sun) on 14th August. On the 15 th August the ‘old' crescent Moon will be close to Venus and will make a good photo opportunity. The phase of the Moon on 15 th August is shown on the Lunar Chart opposite.
MARS rises in the east at about 22:30 but looks small as it is still a long way from Earth. See the chart at the top.
JUPITER rises over the eastern horizon at about 19:00 and will be observable in the south east early evening. A pair of binoculars may reveal the four brightest of Jupiter's moons, Io, Europa, Ganymede and Callisto. A small telescope will allow the moons to be seen very clearly. Jupiter will be close to the horizon but still good for observing. For more details about Jupiter see the June magazine.
SATURN will be visible in the late evening sky rising over the eastern horizon at 19:00. Both of the gas giants will be in the thick, murky and turbulent air close to the horizon. Saturn will be observable but not at its best.
URANUS will not be easy to see this month as it will be close to the southern eastern horizon. It will rise at about 23:00 and be visible for the rest of the night. It will require a clear view to the horizon and modest telescope to see.
NEPTUNE will not be easily visible this month as it will be rising at about 21:00 and will be close to the south eastern horizon in the early hours of the morning.
The Sun rises at about 05:30. A small sunspot was seen towards the end of July.
A small sunspot imaged by SOHO on 26th July 2020
Any activity on the Sun can be found live using the day to day images of the Sun in detail by visiting the very good SOHO website at: http://sohowww.nascom.nasa.gov/ .
THE MOON PHASES DURING AUGUST
Full Moon will be on 3rd August
Last Quarter will be on 11th August
New Moon will be on 19th August
First Quarter will be on 25th August
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