WHAT'S UP THIS MONTH - JUNE 2018

(Link to What's Up May 2018)

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

Click HERE for a downloadable PDF white chart - (Close PDF file to return here)

The chart above shows the whole night sky as it appears on 15th June at 22:00 (10 o'clock) British Summer Time (BST). As 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, marked on the chart as the Zenith (in red). 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 almost just to the west of directly overhead. 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: Venus, Jupiter, Mars and Saturn.

EXPLORING THE NIGHT SKY THIS MONTH

The Southern Night Sky during June 2018 at 22:00 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 at the upper centre of the chart. The curved brown line across the sky at the bottom is the Ecliptic or Zodiac. This is the imaginary line along which the Sun, Moon and planets appear to move across the sky. The constellations through which the ecliptic passes are known as the constellations of the ‘Zodiac'.

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) on the South Eastern horizon.

The planet Venus is in the constellation of Cancer and is very easy to find in the west as soon as the sky darkens.

Ursa Major is almost directly overhead as can be seen by the location of the ‘Zenith' (the point directly overhead) on the chart above. It is one of the best known and easily recognised constellations . It is also known as ‘the Plough' or the ‘Big Dipper' to the Americans. It does actually resemble a saucepan more than anything else and is very easily recognised as a saucepan in the sky.

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. Just follow the ‘Pointers' up and 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. Bo?tes is also a good point to use to find other constellations like Hercules. Hercules is to the east (left) of Bo?tes and is host to the beautiful Globular Cluster Messier 13 (M13).

By following the ‘Pointers' in Ursa Major down they point the way to the constellation of Leo (the Lion). The stick figure of Leo does actually look a little like a lion. 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. Their gravity pulling on each other has made them ‘egg' shaped.

To the east of Virgo is the small and rather indistinct constellation of Libra. This constellation is easy to find this year because it is host to the very bright planet Jupiter. Libra is followed along the ecliptic by the constellation of Sagittarius which is host to the beautiful ringed planet Saturn. There are also a lot of star clusters and other interesting objects in the direction of Sagittarius as this is where the centre of our Galaxy the Milky Way is to be found.

Just coming into view in the east is the Summer Triangle defined by the stars: Deneb (in Cygnus), Vega (in Lyra) and Altair (in Aquila).

THE SUMMER TRIANGLE

The constellations of the Summer Triangle

The chart above shows the sky around the Summer Triangle. The term ‘Summer Triangle' was suggested by Sir Patrick Moore and has now become the best known feature of 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.

THE CONSTELLATION OF AQUILA (the Eagle)

The constellation of Aquila (the Eagle) is found at the bottom corner of the Summer Triangle. There are no interesting objects in Aquila but the one bright star, Altair, has a fainter star above and below it that makes it quite distinct and easy to find.

The constellation of Aquila

THE CONSTELLATION OF CYGNUS (the Swan)

The constellation of Cygnus (the Swan) is located at the top of the Summer Triangle. The brightest star in Cygnus is Deneb which denotes the upper point of the Summer Triangle and represents the Swan's tail. The wings spread from the star Sadr and the head is marked by Albireo. Deneb is one of the largest and brightest stars in our vicinity in our galaxy the Milky Way and is classified as a Supergiant. It is about 25 times more massive than our Sun and has a diameter 60 times that of our Sun. It is located 3000 light years away. As it is so much larger than our Sun it consumes its Hydrogen fuel much faster and consequently shines 60,000 times brighter.

The constellations of Cygnus and Lyra

Cygnus (the Swan) does actually resemble the swan it is supposed to represent. We start at the bright star Deneb which marks the tail of the swan. From the fairly bright star Sadr the wings are spread out to each side and the long neck of the swan stretches on to Albireo.

Albirio 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. This type of double star is much rarer than a pair of stars that are associated, linked by their common gravity and orbiting a common centre of gravity.

The double star Albireo in Cygnus

THE CONSTELLATION OF LYRA (the Harp)

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. Inferred detectors on the IRAS satellite have detected a ring of dust around Vega that may indicate planets are forming around the star.

The constellation of Lyra (small harp)

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 better known as the ‘Lozenge'.

To the south east of the very bright star Vega in the ‘Lozenge' shaped asterism comprised of four stars and 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.

Messier 57 (M57) the Ring Nebula

There are two small constellations called Vulpeculs and Sagitta that are located within the Summer Triangle. They are both small and comprised of relatively faint stars. Vulpecula is rather indistinct but Sagitta is worth seeking out using binoculars.

THE CONSTELLATION OF SAGITTA (the Arrow)

Sagitta is located at the bottom of the Summer Triangle and is good fun to find using binoculars because it really does look like an ‘arrow'. It is composed of three stars that look like the shaft of an arrow and two stars that resemble the flight feathers.

The constellation of Sagitta

The real beauty of Sagitta is how it looks using binoculars but it does host one messier object this is M71 also known as NGC 6838. This is a rather nice but small and faint globular cluster that does need a medium sized telescope to see well. Close to Sagitta is the small and indescript constellation of Vulpecula (the Fox). It is just three stars joined by two lines set at an angle but this does not do justice to the beautiful object within its borders. This is a large Planetary Nebula Messier 27 (M27). It can be found just above the arrow using a good pair of binoculars or a small to medium sized telescope. A dark sky is a great help for seeing M27 more clearly.

Messier 27 (M27) the Dumbbell Nebula

 

THE SOLAR SYSTEM JUNE 2018

MERCURY will be in superior conjunction with the Sun on 6th June and will remain too close to the Sun so will not be observable this month. See the Venus chart below.

VENUS is now rising higher in the west at sunset and is very bright at magnitude -4.0. The telescopic view is not very good because Venus is on the opposite side of the Sun and appearing small. It will become larger but narrower over the next few months. It still requires a Moon filter to reduce the dazzling and sparkling effect and improve the appearance. See the chart below (the sky has been darkened to show the planets).

Venus and Mercury in the west at sunset

Venus is still fairly low in the west after sunset. It passed through conjunction with the Sun on 9th January. This was when it appeared to pass behind the Sun from our point of view. It is still further away than the Sun but moving out from its conjunction with the Sun and towards us. As it moves closer to us it will appear to grow larger in diameter.

Venus showing its orbit as it moves away from the Sun
The phases of Venus as it draws closer to us

As Venus loops up and towards us over the next few months it will appear to get bigger but will also change to a progressively thinner crescent. It will appear bigger and thinner but remain at the same overall brightness. While it is still further away than the Sun the side of Venus facing us will be fully illuminated by the Sun. When Venus is at the same distance as the Sun (they appear side by side) the half of Venus facing towards the Sun will be illuminated. As it moves closer to us the illuminated side will begin to disappear from our view and we will see more of the dark side (night) and Venus will appear Gibbous (as in the left image of the phases shown above). Eventually Venus will appear as a thinning crescent as the illuminated side progressively disappears and the planet moves between us and the Sun. At this later stage Venus will appear quite large in diameter.

MARS will rise in the south east at 23:00, following Saturn but will be lost in the brightening sky by 04:00. See the Saturn chart below. The Red Planet is appearing larger at 19.0 arc-seconds in diameter and will brighten to magnitude -1.6. Mars is low and in the turbulent air but is starting to look larger. The surface markings are just starting to become visible.

JUPITER is now a good evening and early morning object. It rises over the eastern horizon at about 16:30 and will be observable in the south east as the sky darkens. 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 at 22:30 BST on 15th June

Jupiter was at opposition at midnight on 9th May (01:00 BST). This means it was due south when the Sun is due north (but below the horizon). Earth was overtaking Jupiter on the inside of the orbit of Jupiter. Jupiter was at its best position for observing at that time. Jupiter's largest moons Io, Europa, Ganymede and Callisto can also be seen transiting (passing in front of Jupiter) and being occulted (passing behind Jupiter) using a small telescope. The times of these events can be found using a planetarium application.

SATURN will be visible in the early morning sky close to the south eastern horizon. The ringed planet rises in the east at about 21:30 this month. The view of Saturn will not be good this year as it will be close to the horizon. It will be observable in the south east from 23:00 until the sky begins to brighten at about 03:00.

Mars, Saturn and Jupiter at 01:00 BST on 15th June

URANUS will not be observable this month as it is still too close to the Sun after its conjunction with the Sun April.

NEPTUNE will not be easy to see this month as it rises over the south eastern horizon at midnight so it will be in the brightening sky before the Sun rises at 03:40. It will need a telescope to see it as a small blue disc.

THE SUN

There were a few small sunspots visible during April but the main active phase of the Solar Cycle is now over.

The Sun rises at about 03:45 the whole of this month and will be setting at 20:20 during the whole of this month. The Summer Solstice (Midsummer Day) will be on 21st June when the Sun reaches its highest position in the sky.

THE MOON PHASES IN JUNE

Last Quarter will be on 6th June

New Moon will be on 13th June

First Quarter will be on 20th June

Full Moon will be on 28th June

The thin crescent of the New Moon should be visible in the west after sunset on the 15th June and will be a good target for binoculars or a small telescope. See the Venus chart above.

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