WHAT'S UP THIS MONTH - 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 June 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: None.

 

EXPLORING THE NIGHT SKY THIS MONTH

The Southern Night Sky during June 2020 at 20:00 BST

The chart above shows the night sky looking south at about 22:00 BST on 15th June. 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 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 from east to west. The constellations through which the ecliptic passes are known as the constellations of the ‘Zodiac'.

June is not the best month for looking at the night sky for two reasons. Firstly the Summer Solstice occurs on 20 th June so this is Midsummer Day. This day will be the longest day of the year which means it is also the shortest night of the year. As a consequence the night sky does not get completely dark. So the Sun sets late and twilight lasts all night and it will not be fully dark.

Constellations through which the ecliptic passes this month are: Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin), Libra (the Scales) and Sagittarius (the Goat) rising over the South Eastern horizon.

Ursa Major is very easy to find and because it is ‘circumpolar' (never sets below the horizon) it is always somewhere in our night sky. As it is so easy to find it is a good place to start exploring the night sky. The two stars of the ‘pan' opposite the ‘saucepan handle' (known as the Pointers) can be used to find Polaris the Pole Star (or North Star) in Ursa Minor. Follow the ‘Pointers' (the two stars in the pan of the Saucepan) up out of the pan to find Polaris. By following an imaginary line off the end of the saucepan handle will show the way to Arctaurus the bright red star (it looks more orange) in Bo?tes.

The constellation of Bo?tes does not have anything interesting to search out but the bright star Arctaurus is very beautiful. It is a Red Giant and appears distinctly orange to the naked eye and even more so when using binoculars or a telescope. If the binocular or telescope is moved slightly out of focus Arctaurus will look even more orange . Arctaurus is bright and easy to find in the sky so it can be used as the starting point to begin exploring the night sky.

Marked on the chart above is the ‘Summer Triangle' which is the most prominent feature in the summer sky. The term ‘Summer Triangle' was suggested by Sir Patrick Moore and has now become the starting point for exploring the summer night sky. The corners of the imaginary triangle are positioned on the three obvious bright stars: Deneb in the constellation of Cygnus, Vega in Lyra, and Altair in Aquila. The Milky Way (our Galaxy) flows through the Summer Triangle and passes through Aquila and Cygnus.

By following the ‘Pointers' in Ursa Major down (instead of up for Polaris) they point the way to the constellation of Leo (the Lion). The stick figure of Leo does actually look a little like a lion (or the Sphinx in Egypt). The bright star Regulus in Leo sits right on the Ecliptic and is often seen close to the Moon and sometimes the planets as they appear to move along the Ecliptic.

To the east of Leo is the quite indistinct constellation of Virgo. It does have one fairly bright star called Spica. It is classified as a Class B1 Giant but is in fact a very close binary star. The two stars are very close and orbit the common centre of gravity every four Earth days. Powerful gravity at close proximity is pulling on each star and has made them ‘egg' shaped.

JUPITER AND SATURN ARE COMING INTO VIEW

Jupiter and Saturn rising at 1:30 BST on 15th June

Jupiter and Saturn are now moving into view just after midnight and will be in position for observing in 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 is visible in the early morning, rising in the east around midnight in June. It will be observable in the east about an hour or so later at around 01:30 BST 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. By about 02:30 Jupiter will have risen high enough in the south to 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 imaged by Steve Harris .

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 the orbit Jupiter in 1.77 days, 3.55 days, 7.16 days and 16.69 days respectively.

Jupiter and the Galilean Moons as they may appear using a small telescope image Steve Harris

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 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.

 

THE SOLAR SYSTEM THIS MONTH

The planets observable in the early morning sky

MERCURY will be quite difficult to see in the bright sky soon after the Sun sets over the western horizon. The best time to look for the smallest planet is in the first part of the month as it will be at its greatest eastern elongation (furthest from the Sun) on 4th June. Remember do not look for Mercury using binoculars until Sun has completely set over the western horizon.

Mercury at sunset on 15th June

VENUS will be very low in the east as the sky brightens before the Sun rises and will not be easy to observe. It now appears as a very thin crescent but has a large diameter as it is moving into Inferior Conjunction with the Sun (between Earth and the Sun) on 3rd June.

Venus imaged by Steve Knight 2020 05 21

MARS Rises is the east at about 01:30 but is looking rather small as it is still a long way from Earth but is gradually getting closer. See the chart at top.

JUPITER rises over the eastern horizon just before midnight 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 is observable in the early morning sky until the sky brightens at about 04:00.

SATURN will be visible in the early morning sky before sunrise rising over the eastern horizon at 23:30 at the beginning of June and 22:00 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.

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 04:45 throughout the month as it will be midsummer. Midsummer Day (the Summer Solstice) will be on 21st June. This is the time when the Sun appears to reach its maximum height above the southern horizon at midday 13:00 BST (12:00 GMT).

THE MOON PHASES DURING JUNE

Full Moon will be on 5th June

Last Quarter will be on 13th June

New Moon will be on 21st June

First Quarter will be on 28th June

 

The New Moon as it appeared in the west on 24th May 2020 Imaged Steve Harris

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