WHAT'S UP THIS MONTH - JULY 2020

(Link to What's Up June 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 July 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 in the evening sky: Jupiter, Saturn and Mars .

EXPLORING THE NIGHT SKY THIS MONTH

The Southern Night Sky 14th July 2020 at 01:00 BST showing Jupiter at opposition

One of the Constellations of this Month is one of the best known of all the constellations and is certainly one of the most recognisable . It is Ursa Major (the Great Bear) also known as the ‘Plough' or ‘the Big Dipper' in the USA. It has very little resemblance to a bear and looks much more like a ‘Saucepan' and appears larger in the sky than might be expected.

Ursa Major is almost overhead at this time of the year as can be seen by the chart above. The point in the sky directly overhead of the observer is called the ‘ZENITH' and is shown in red on the chart. Ursa Major is a circumpolar constellation, this means it never disappears below the horizon from the UK and so is always visible somewhere in the night sky throughout the year. 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).

The sky rotates around Polaris once a year due to Earth's orbit around the sky. Polaris can always be found by finding Ursa Major. Then by following the two stars opposite the handle of the ‘saucepan shape', up out of the pan and looking about five times the distance between the two pointer stars that are called Dubhe and Merak in Ursa Major. See the chart above.

Our planet Earth rotates around the North Celestial Pole once a 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. It will appear to move anticlockwise around Polaris as shown on the chart above (handle behind). The movement is slow and not perceivable in real time.

The chart shows the sky as it will appear at 01:00 on 14th July this is the time when the planet Jupiter will be at opposition. This is the point where Earth will be overtaking Jupiter on their orbits around the Sun. At this time Jupiter will be at its closest to Earth and at its best position for observing. Saturn will be at its opposition on the 20th July when it will be at its best. See the article about the oppositions of Jupiter and Saturn.

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. 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, Mars and Neptune.

JUPITER AND SATURN ARE COMING INTO VIEW

Jupiter and Saturn rising at 22:00 BST on 15th July 2020

Jupiter and Saturn are now moving into view before midnight and will be in good position for observing by midnight and into the early hours. Jupiter will reach Opposition on 14th July when it will be at its very best. Opposition is the exact time that Earth will be overtaking Jupiter on the respective orbits of the two planets. Earth's angular speed is much greater so travels faster on its smaller orbit around the Sun. It therefore catches up and overtakes Jupiter about every 13 months.

At this time of year the ‘Ecliptic' (the imaginary line along which the Sun, Moon and planets appear to move across the sky) is low in the sky during the night due to the 23.4º tilt of Earth's axis. The ecliptic is high during the day which is why the Sun appears high in the summer sky. With the ecliptic low at night Jupiter appears low in the sky and in the relatively thick, misty and turbulent air closer to the southern horizon.

Jupiter will be rising at about 21:00 in the east and at its best around midnight. It will be observable in the east about an hour or so after is rises when it is higher in the sky. Jupiter is easy to find as it is very bright, in fact it is the third brightest object in the night sky after the Moon and Venus. Jupiter will not rise very high above the southern horizon so will be in a reasonable but low position for observing in the constellation of Sagittarius (the Archer ).

A good pair of 9 x 50 binoculars will just about show the four bright moons known as the Galilean Moons. These four bright moons are called the ‘Galilean Moons' after Galileo Galilei who first recorded seeing them.

Jupiter and the Galilean Moons 23:00 on 15th July 2020

OBSERVING JUPITER USING BINOCULARS

Using binoculars to observe Jupiter is better if you prepare first. There are two things that can help improve the view. The first is to set up the binocular to suit your eyes.

The right hand eyepiece can be rotated to adjust the focus of each optical body to suit each eye this is called ‘dioptre adjustment'. The way to do this is to find a bright star in the binocular (or any distant object can be used during the day). Close the right eye and adjust the focus to suit the left eye using the central focusing barrel. When the sharpest image is achieved (a star is the smallest point of light) open the right eye and close the left. Now rotate the right eyepiece by turning the dioptre adjuster [on the right eyepiece] each way until the sharpest image is achieved in the right eye. Now open both eyes and adjust the focus to suit both eyes, using the central focusing barrel only, to check the quality of the view. The binocular is now adjusted to suit both your eyes and it should look clearer.

The second thing to try is to provide extra support for the binoculars. One option is resting your elbows on a solid object such as a wall or fence. If this is not possible stand against a wall and steady the binocular or your hand against the wall to stop shaking movements.

The best possible answer is to support the binocular on a stand of some sort. Even a cheap camera tripod can be used perhaps utilising an elastic strap (Aerolastic) or any other means to secure the binocular to the support. This will help steady the binoculars. It may even be found that the view is improved by sitting in a reclined garden lounger and somehow supporting the elbows.

Binoculars will just about show the moons and may just reveal the two darker equatorial belts if using larger binoculars.

OBSERVING JUPITER USING A TELESCOPE

For those who a lucky enough to have access to a telescope Jupiter is one of the most impressive things to see in the night sky. Even a modest telescope will show the coloured cloud belt and Zones. The four brightest moons can be observed as they orbit the Giant Planet.

The Belts and Zones are regions of higher and lower atmospheric pressure. The lighter coloured ‘Zones' are regions of rising gas caused by convection of heat from the core of Jupiter. The darker ‘Belts' are regions of falling gas and are approximately 20 kilometres lower in altitude than the Zones. In the regions where the belts and zones meet, huge storms are created as the gas in the belts and zones moves at different speeds and directions. A larger telescope will allow some detail of the storm patterns to be seen.

The cloud markings on Jupiter

The most famous feature in the cloud system is the ‘Great Red Spot' (GRS). This huge storm has been raging for over 350 years. We know this because it was recorded by astronomers in 1664 using some of the earliest telescopes. The GRS does change its colour, size and shape but it is always there. Its colour may fade from the normal pink to nearly white when it may almost disappear. The colour is thought to be caused by Phosphorus welling up from deep regions in Jupiter's atmosphere.

The four bright ‘Galilean Moons': Io, Europa, Ganymede and Callisto can be seen quite easily even using a small telescope. They can be followed as they orbit Jupiter in 1.77 days, 3.55 days, 7.16 days and 16.69 days respectively.

Jupiter and three of the Galilean Moons as they may appear using a small telescope

Io is the innermost of the four large moons that Galileo discovered and is the second smallest at 3,630km in diameter which is slightly larger than Earth's Moon which is 3,476km. Io orbits Jupiter every 1.77 Earth days at a distance of 421,000km from Jupiter. When seen up close the surface resembles a pizza. Io is the most volcanically active body in the Solar System.

Europa is the second large moon out from Jupiter and is the smallest of the four at 3,138km in diameter (slightly smaller than our Moon) . The ice on the surface reflects 10 times more sunlight than the surface of our moon, making its surface the brightest of Jupiter's moons.

The moon is thought to be comprised mainly of water ice and is believed to have a 70 to 100km thick layer of water and ice that covers the surface of this, the smoothest moon in the solar system. The surface is criss-crossed with huge cracks thought to be caused by powerful tidal forces produced by the gravity of Jupiter. Radar scans have indicated that there may be a liquid salty water ocean beneath the 20km to 30km thick water ice crust.

Ganymede is the largest moon in the solar system (5,263km in diameter). It orbits Jupiter in about 7.16 (Earth) days at just over 1 million km from Jupiter. Ganymede is the only moon known to have a magnetosphere and that indicates it may have a hot (<1500°K) liquid Iron core. Polar ice caps have been detected that may be formed by water molecules migrating along the magnetic force lines and being deposited at the poles. There may be a multilayered water and ice surface layer up to 800km deep. It is suspected that there may be a deep liquid layer of water at the ice / rock interface.

Callisto unlike the other three large moons, appears not to have any noticeable internal activity or source of heat. Consequently the surface is old and has one of the most heavily cratered surfaces in the Solar System. Callisto is a large moon with a diameter of 4,800km orbiting Jupiter at 1.8 million km and takes 16.69 (Earth) days to complete each orbit.

Sometimes we can see the moons pass in front or behind Jupiter on every orbit and not above or below as they do for a lot of the time. This makes observing Jupiter very interesting. We can watch the moons approach the planet to disappear behind or in front of Jupiter and then watch them reappear an hour or two later. We can also see their shadows as they pass in front and project their shadow on to the planet. These events can be predicted using a planetarium application and the events can then be followed and timed using a fairly modest telescope.

Eclipse occurs when a moon casts its shadow on to Jupiter. It is quite easy to see because the eclipse shadow looks like a black full stop against the bright glare of the surface of the planet. Moons can also be eclipsed and disappear as they pass through the very large shadow cast by Jupiter.

Transit occurs when a moon passes in front of Jupiter. The moon is actually very difficult to see while it is in front of the planet as it is lost in the glare from the surface.

Occultation occurs when a moon passes behind the planet. An Occultation or Transit is easy to follow with a telescope as the moon approaches Jupiter.

 

SATURN (The Ringed Planet)

Saturn the beautiful ringed planet

Saturn, with its magnificent ring system, is surely the easiest planet to recognise. Any poster or cartoon depicting a space scene will almost certainly have a planet with a ring system looking somewhat like Saturn. The large outer planets also have ring systems but these are all feeble compared to Saturn's.

Saturn is the second largest planet in our Solar System after Jupiter. The planet itself is 120,000 km in diameter at the equator but is flattened to 108,000 km at the poles due to its rapid rotation. Although Saturn is 10 times the diameter of Earth it rotates on its axis (1 day) in only 10 hours 14 minutes. The rings are 275,000 km (170,000 miles) across but are mostly less than 30 metres thick. To put this in perspective, the ring diameter is about ¾ of the distance from Earth to the Moon. The rings are made up of millions of small pieces of mainly water ice and varying in size from a few millimetres to a few metres across.

Like Jupiter, Saturn is a gas giant planet. This means it has no solid surface that a probe craft could land on. The majority of the planet (96.3%) is made up of Hydrogen gas with 3.7% Helium and traces of Ammonia and Methane. The cloud markings are more subtle than those on Jupiter and need a larger telescope to discern clearly.

Saturn is approximately ten times further out from the Sun than Earth therefore we always see Saturn fully illuminated and never see phases. However we do see the rings from a different aspect over the course of Saturn's 29.46 (Earth) years orbit around the Sun. As Saturn is so far away from us and we are a lot closer to the Sun, we view Saturn almost as if we are at the same position as the Sun. Saturn has a 27.6° tilt but is always tilted in the same direction as it orbits the Sun. Therefore as we look out from our position, close to the Sun, Saturn's ring appears to tilt up and down as Saturn orbits the Sun every 29.46 years.

Observing Saturn does need a telescope to see the ring system. The bigger the telescope the more detail will be seen. The ring system can be seen using a 100mm aperture telescope and about 1000mm focal length. Saturn's largest moon Titan can be seen but another four or five moons can be seen using a larger telescope. Unfortunately Jupiter and Saturn are very low and close to the horizon so the views will not be good due to atmospheric turbulence.

OBSERVING SATURN

Saturn can be seen with our ‘naked' eyes as a bright and slightly yellow looking star. This year it is very close to much brighter Jupiter so that will help to find the ringed planet. A pair of binoculars will show Saturn looking brighter and that it is not a star as it will appear slightly ‘fuzzy' but the ring system will not be visible using binoculars. Saturn will be rising over the eastern horizon at about 21:20 this month and will be in a position for observing about one hour later.

Saturn is one of the most beautiful and impressive objects to look at through a telescope and really does have the ‘Wow!' factor, especially when seen using a larger telescope. Even using a small telescope the ring system can be made out but a high magnification is required on any telescope. For many people their first sight of Saturn was the thing that encouraged them to buy their first telescope.

During recent months the sky has been graced with the magnificent views of Jupiter the ‘King of the Planets' and Saturn close together in the morning sky. In some ways our expectations of observing Saturn could be diminished by the stunningly bright and colourful views of Jupiter that we have been accustomed to. Jupiter is much more impressive than Saturn for a number of reasons.

First Jupiter is bigger than Saturn. Jupiter is 142,984 km in diameter and Saturn is 120,536 km but this is not the full story. Saturn is also about twice as far away from the Sun compared to Jupiter. Jupiter orbits at 778 million km whereas Saturn's orbit is 1429 million km from the Sun. This means that Saturn receives only a quarter of the amount of light, per square metre, that Jupiter receives.

The greater distance of Saturn also means that the amount of light that we see reflected back from Jupiter is four times that reflected by Saturn. In total this means that Saturn not only appears much smaller but is also more than 16 times fainter than Jupiter. So that is the bad news but this is compensated for by the magnificent ring system of Saturn that does add a little to the brightness and can be seen even in smaller telescopes.

Saturn can be seen in a smaller telescope of the sort that a beginner to astronomy might have been advised to buy as a first telescope by experienced astronomers. This sort of telescope would be a 100mm refractor or a 150mm reflector with a focal length of about 1000mm. A high magnification must be used and on a good clear and still night the view will be very rewarding. The picture below shows the sort of image that can be expected in one of these first telescopes along with an example of the view through a larger aperture telescope and with a longer effective focal length.

Saturn viewed through a 100mm and a 200mm aperture telescope

As with all targets, finding Saturn with a telescope starts with locating the planet with the finder. Next use a low power eyepiece (e.g. 25mm) and centralise Saturn in the field of view of the main telescope. Carefully remove the low power eyepiece and fit a high power (10mm) eyepiece into the focuser. Again centralise the planet and adjust the focus until the image is as clear as possible. If Saturn is observed earlier in the evening the image may be difficult to focus due to air turbulence close to the horizon or above roof of a nearby house. The image should improve slightly as Saturn rises a little higher in the sky and as the telescope cools.

If the seeing conditions are good it may be possible to remove the high power eyepiece and fit a Barlow Lens into the focuser and then refit the high power eyepiece into the Barlow. The focuser will need to be moved in about a centimetre to compensate for the Barlow then refocused. The Barlow will have the effect of doubling the magnification of the eyepiece and therefore double the size of Saturn.

Up to six of Saturn's moons may be visible, distributed around the planet. The largest moon Titan (the second largest in our Solar System) is the easiest to see. Some of the others may be difficult (but possible) to see in a smaller telescope. On a good clear night it may be possible to see Titan and two or even three others in a 90mm refractor or a 113mm reflector. The other two will need a larger telescope to see.

Some of Saturn's Moons on 20th July 2020

The chart below shows the position of Saturn and Jupiter on 20th July. At 22:00 BST (23:00 GMT) and is the exact time when Earth will be overtaking Saturn. For about one hour the rings will brighten because the sunlight will be reflected directly back towards the Sun and Earth. This is called the Seeliger Effect and well worth look out for.

Saturn at Opposition at 22:00 on 20th July

THE SOLAR SYSTEM THIS MONTH

The night sky at 01:00 showing the positions of the planets

MERCURY will be difficult to see in the bright sky before sunrise on the north eastern horizon. See the chart below.

Mercury and Venus at sunrise on15th July

VENUS will be very low in the east as the sky brightens before the Sun rises and will not be easy to observe see the image above.

MARS rises at midnight and looks small as it is still a long way from Earth. See the planet positions chart above.

JUPITER rises over the eastern horizon at about 21:30 and will be observable in the south east. A pair of binoculars will 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 observable in the early morning sky until the sky brightens at about 04:00. For more details about Jupiter see the detailed Jupiter article above.

SATURN will be visible in the late evening sky rising over the eastern horizon at 22:00 at the beginning of June and 20:30 at the end of the month. Both of the gas giants will be in the thick, murky and turbulent air close to the horizon. Saturn will be observable, in the south, through the rest of the night until sunrise. See the Saturn article above.

URANUS will not be easy to see this month as it will be close to the southern horizon in the early hours before sunrise. It will require a clear view to the eastern horizon and the alarm to be set very early.

NEPTUNE will not be easily visible this month as it will also be close to the southern horizon in the early hours of the morning. Being close to Mars will help find it.

THE SUN

The Sun rises at about 05:00. There was a small sunspot in May, the first for quite some time. Activity on the Sun can be followed live with day to day images of the Sun by visiting the very good SOHO website at: http://sohowww.nascom.nasa.gov/ .

THE MOON PHASES DURING JULY

Full Moon will be on 5th July

Last Quarter will be on 13th July

New Moon will be on 20th July

First Quarter will be on 27th July

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