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June is significant for Astronomers in may ways.  For those of us who find ourselves in the Northern Hemisphere, June is the lightest part of the year.  This owes itself to the Summer Solstice falling on the 21st June for the Northern Hemisphere.  At this point, the Sun reaches the most northerly point in the Ecliptic and its highest separation from the horizon at Midday.  Of course, for every action, there's an equal and opposite reaction - while we Northerners bask in the glory of Midsummer, those in the Southern Hemisphere are in the grip of Midwinter.  The cause of these extremes - and all our seasonal weather on Earth - is our planets' rotational tilt (around 23.5 degrees from vertical) in comparison to the plane of our orbital path around the Sun.  During the Summer time, the leading hemisphere is pointed towards the Sun, thus receiving more light to warm up the land and sea.  Days are subsequently longer and nights are shorter, the further towards the pole you find yourself.  In Midsummer, those above the Arctic Circle experience 24 hour daylight.  Of course, the opposite is true for all of this if you find yourself in the trailing hemisphere.

 

 

This has noticeable effects on the quality of darkness for those in temperate Northern latitudes, as during this point of the year, the Sun, even at the deepest point of the night is not so far below the horizon.  For those in the Northern Europe and the Northern parts of the USA and Canada and Asia, this can mean permanent Astronomical Twilight for a while around the Summer Solstice.  

 

From the 23rd of May to 21st July 2015, there is a state of permanent Astronomical Twilight for those in Southern UK latitudes (around 51 degrees N), which means that the Sun is less than 18 degrees below the horizon all night long.  This means that the skies are never truly dark and that objects around or below the 6th magnitude are unable to be distinguished with the naked eye.  This obviously has knock-on effects for deep sky observation and astrophotography.  The further north one observes from, the longer this period of permanent Astronomical Twilight persists: in Manchester UK (latitude 53.5 degrees N) this extends from 14th May to 30th July; in Edinburgh (just shy of 56 degrees N) the period is yet longer, from May 5th to August 9th.  Do bear in mind, if you find yourself in latitudes similar to Reykjavik, Iceland (64 degrees N) Astronomical Twilight persists from 10th April to 2nd September - pretty extreme!  North of the Arctic Circle, the Sun will not set at all around the Solstice, whereas south of the Antarctic Circle, the Sun won’t rise at all during this period.

 

The Moon

 

The Moon begins June at First Quarter phase on the 1st, a resident of the constellation of Leo.  Transiting a little before sunset, the Moons in a good place for observation in the early evening.  

 

A few days later on the 3rd/4th June, the Moon passes Jupiter in Virgo, skimming just under two degrees to the north of the planet.  This reasonable conjunction will make a pretty pairing for observation and astrophotography, though is not of any great scientific importance.

 

The Moon and Jupiter, Midnight (BST) 4th June.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, www.southernstars.com.


The Moon becomes Full on June 9th, so coupled with the lack of much in the way of true darkness for many in the northern hemisphere at this time of year, makes this a relatively poor time for deep sky observation and astrophotography.

 

The Moon reaches Last Quarter on 17th June, while resident in Aquarius.  From this point, it slips towards the Sun, becoming New on the 24th, when both objects are to be found in Gemini.  

 

The Moon spends the last few days of June swiftly passing through Gemini, Cancer, Leo and on into Virgo, where in can be found on the closing day of the month a few degrees to the west of Jupiter at sunset.  It is just before First Quarter phase on the 30th June.  As the Sun has climbed higher north in the ecliptic, the Moon now does not appear quite as high in the evening sky at Waxing Crescent phase as it has done in preceding months.  The “High Spring Crescent” of Springtime is over - a sure sign that Summer is here. 

 

The Planets

 

Mercury

 

Mercury, at -0.3 mag, but just over 5 degrees high at sunrise (from 51 degrees N), presents a difficult target for those of us in temperate northern climes, at the beginning of June.  Although nearly 21 degrees angular separation from the Sun, the innermost planet is still very low in the east at sunrise and will be difficult to pick out in the dawn sky.  Still, for those in a more southerly or tropical locations, the planet will be exceptionally well-positioned for observation.

 

As June progresses, Mercury dips towards the Sun, brightening as it goes. By mid-month, the planet reaches an extremely bright -1.5mag, though will sit just under 8 degrees from the Sun on the 15th.

 

Superior Conjunction of Mercury occurs on the 21st June, when it will be on the opposite side of the Sun to us here on Earth.  Beyond this point, Mercury re-emerges into the evening sky.

 

By the end of June, Mercury has climbed into the evening sky, though at just under 11 degrees from the Sun on the 30th, despite a healthy brightness of -1.1 magnitude will still be a challenge to find.  Sitting at just under 6 degrees elevation at sunset (from 51 degrees North) on the 30th, the planet will remain a tricky target until later in July when its angular separation from the Sun has increased somewhat.  If you have a flat westerly horizon, do by all means try to find Mercury, though make sure the Sun is well and truly set before attempting to locate the planet.

 

 Mercury at Sunset, 30th June 2017.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, www.southernstars.com.


Venus

 

Venus is to be found in Pisces on June 1st, shining at a dazzling -4.3 mag and displaying a 24.5 arc second diameter, 48.3% illuminated disk - just shy of half phase.  It stands around 14 degrees high (from 51 degrees N), almost due east at sunrise and won’t be difficult to make out in the dawn sky.

 

By mid-June, Venus’ angular separation from the Sun stands at just under 45 1/2 degrees and the planet is still showing a healthy-sized disk of 21 arc seconds diameter, and although it has increased its phase to 55.6% illumination, the steady march of Venus away from Earth on its faster interior orbit means that inevitably it is dropping brightness - it is now -4.2 mag - still an impressive sight, but noticeably less bright that it was earlier in the year.  At a little under 16 3/4 degrees elevation, due east at dawn it won’t be a difficult target to pick out in the dawn sky.

 

By the end of the month, Venus will have faded to -4.1 mag, still brighter than anything else in the sky bar the Sun and Moon, but a definite decline from the beginning of the month.  By now it is just 18.3 arc seconds in diameter and is to be found 136.5 million km from Earth.  Standing at over 20 degrees elevation (from 51 degrees N), it will still dominate the sky around dawn and will be well-placed for both telescopic observation and imaging.

 

Venus at Sunrise, June 30th 2017.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, www.southernstars.com.


Mars

 

Mars reaches Superior Conjunction on July 27th, so we are now approaching our furthest point from the Red Planet.  As such, Mars is a disappointingly dim +1.7 mag and 3.7 arc seconds diameter disk in the evening sky at sunset, setting under two hours after the Sun on June 1st.

 

By the time we reach the end of the month, Mars is just 8 degrees to the east for the Sun and will be impossible to observe in the evening sky.  After the end of July 2017, Mars will reappear in the morning sky and we start the long countdown to Martian Opposition in July 2018.

 

Jupiter

 

We find Jupiter in Virgo, shining a a healthy -2.2 mag, at a little over 40 arc seconds diameter on 1st June.  Transiting at just past 9pm in the evening, the planet will reward early evening observations.

 

By the 15th June, nothing much has changed as far as Jupiter is concerned: the planet has dropped fractionally below 40 arc seconds diameter, but is still holding strong at -2.2 mag.

 

 

Jupiter at Sunset, 15th June 2017.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, www.southernstars.com.

At the end of June, Jupiter will have dimmed fractionally to -2.1 mag and shrunk to 37.4 arc seconds diameter as we draw away from it on our faster interior orbit.  The King of the Planets now transits at just past 7.15pm.  Jupiter is joined by the waxing First Quarter Moon in Virgo on the 30th, being found a little over 7 degrees from each other during the night.

 

Saturn

 

Saturn comes to opposition on June 15th 2017, so we on Earth are now approaching our closest point to this fascinating ringed world.  Beginning the month as a +0.1 magnitude, 18.3 arc second diameter object in Ophiuchus, Saturn is in prime position for observation in the southern hemisphere, whereas those of us observing the planet from the northern hemisphere will not see it as well.  Saturn will be very low in the south from a northern hemisphere perspective, but will still be a rewarding target to pick out, as long as you have a decent southernly horizon.

 

Saturn transiting on Opposition night, 15th June 2017. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, www.southernstars.com.

Opposition neatly occurs in the middle of the month, on the night of the 15th.  By this point Saturn will be at a maximum brightness of +0.0 mag and 18.4 arc seconds diameter.  With its ring system presented at a very wide angle to us, Saturn is a breathtaking sight and is at its maximum brightness and angular size.

 

Saturn and Moons, Opposition night, June 15th 2017.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, www.southernstars.com.

By the end of June, Saturn has faded fractionally to +0. Mag and shrunk to 18.3 arc seconds diameter.  The good news is that the planet now transits at just before midnight, making it better placed for evening observation.  Saturn will continue to rise earlier and earlier as the year progresses.

Saturn, imaged through 80mm Explore Scientific Triplet.  Image Credit: Kerin Smith

 

Uranus and Neptune

 

Both Uranus and Neptune are most definitely morning objects. Neptune, the fainter but more westerly target is resident in Aquarius and at +7.9 magnitude and 2.3 arc seconds diameter, rises just under 3 hours before the Sun on the 1st of the month.

 

Uranus is further east in neighbouring Pisces, but although it is brighter at +5.9 mag and 3.4 arcs seconds diameter, is more challenging currently, as it rises just over an hour and a half before the Sun.

 

Uranus and Neptune, predawn, 30th June.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, www.southernstars.com.

By the end of the month, both planets are distinctly easier to find.  Neptune rises at just before midnight from temperate latitudes and is heading for the N/S transit point as the Sun rises.  Uranus is fractionally brighter at +5.8 mag and now rises around 3 1/2 hours before the Sun. 

 

Comets

 

Comet C/2015 ER61 PanSTARRS is to be found in Pisces.  There is some debate at time of writing as to exactly how bright it will appear in the sky during its visit to the inner solar system.  Supposedly having peaked in brightness in the latter part of May, the comet has a theoretical maximum magnitude of +6 mag, +/- 2 magnitudes - quite a large margin of error.  This comet should be past peak magnitude at the beginning of June, but will be worth keeping an eye on in the morning sky, where it rises around 2 1/2 hours before the Sun on the 1st of the month. Venus provides a convenient and unmissable signpost as to the part of the sky the comet is in - with the comet being around 10 degrees to the north of the planet on the 1st.  As the month progresses, the comet will be fading in brightness - so keep an early look at for it.

 

Comet C/2015 ER61 PanSTARRS path through Pisces and Aries, June 2017 (comet position shown 1st June).  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, www.southernstars.com.

Comet C/2015 V2 Johnson should still be an easy binocular object in Boots during the early part of June, hovering around the +6.7 mag mark.  During the first week in June it will be around 5 degrees to the east of Arcturus, Alpha Bootis in the sky and should be easy to find in the sky as it crosses the meridian at a little after 10pm in the evening.  By mid-month it will have faded fractionally, but is still easy to find on the borders of Bootes and Virgo (it actually crosses the constellation boundary into Virgo on the 14th June).  By the night of the 30th, as seen from temperate northern latitudes, the comet will cross the meridian line roughly in line with Spica, Alpha Virginis, from which it will sit just under 12 degrees to the east.  By this point in the it will probably be around half a magnitude fainter than it was at the beginning if the month, but will still hopefully be a rewarding target to observe.

 

Comet C/2015 V2 Johnson path through Bootes and Virgo, June 2017.  (comet position shown 1st June).  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, www.southernstars.com.


Noctilucent Clouds

 

Noctilucent Clouds are often seen in June - their bright gossamer-like structures can normally be seen low on the northerly horizon, between latitudes of 50-65 degrees, when the Sun is between 6 and 16 degrees below the horizon.  These clouds are mysterious - there were no recorded sightings of them before 1885.  Some researchers believe they are formed as a result of volcanism, human-induced atmospheric pollution, or even the condensation of water vapour along the trails of meteors.  Whatever their origins, now is the best time to see them from Northern latitudes.  Interestingly, whilst Noctilucent Clouds have been observed in the Southern Hemisphere, their incidence appears much, much less than their Northern Hemispherical counterparts.  Whatever their origins, now is most definitely the right time to witness their ghostly displays.

 

 

Deep Sky Delights in Draco and Hercules

 

June is not the best time for observing really challenging Deep Sky objects from the Upper Northern Hemisphere, due to the Summer Solstice and the lack of true astronomical darkness, but there's still plenty to see, even if the sky is not at its darkest.  Those readers in the Southern Hemisphere will have to forgive this rather Northerly-biased guide this month - rest assured, there's plenty of Southerly objects coming in July's guide! 

 

Draco and Hercules.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, www.southernstars.com.

We start almost as Northerly as one can get in the heavens, in Draco, the constellation of the Dragon, which winds its serpentine way around its polar neighbour, Ursa Minor.  As many reader will no doubt be aware, the Pole Star of both hemispheres shifts due to the precessionary wobble of our Earth's axis.  Whereas Polaris is now the closest visible star to the Northern Celestial Pole, in times past - around 6000-4100 hers ago, Thurban, Alpha Draconis was.  Thurban is one of those seemingly disappointing Alpha-classed stars, as it is clearly fainter than others within Draco.  It's possible that the fact that it was a Pole star is the reason it was treated with such reverence - it may be possible it was once brighter, though this in itself is less likely.  

 

Despite being a large constellation, Draco has few Deep Sky highlights, in comparison to those that seemingly litter the constellations surrounding it. But those that it does have are interesting ones and well worth seeking out.  The first of these is M102 or NGC5866, otherwise known as the Spindle Galaxy.  The popular name is somewhat misleading as there are two other galaxies, one in neighbouring Ursa Major and another in Sextans - though it definitely appears spindle-like in telescopes.  M102 is an edge-on spiral galaxy, of +9.9 mag brightness and occupying an area of 6.5 x 3.1 arc minutes.  Although it may not seem especially bright, its condensed nature means it can be found in relatively small telescopes and is excellently-seen in medium and large instruments, which can resolve the dark lane bisecting its core with ease.  In this respect, M102 is very similar to NGC9891 in Andromeda and NGC4565 in Coma Berenices.

 

The Spindle Galaxy, M102, Hubble Space Telescope.  Image credit: NASA/ESA, Public Domain

M102 is one of the latter controversial Messier objects and its discoverer, Pierre Mechain later rather dismissively recanted its classification, claiming that the object in question was a mistaken duplication of the nearby M101.  However, if we examine Mechain's original notes and the exact position of M102 as described by Messier himself, then it is clear M101 cannot match the reported object in question.  Messier expert and Harvard Emeritus Professor of Astronomy Owen Gingerich put forward NGC5866 as a worthy "best fit" candidate for M102 after extensive study of Messier's original notes and the correspondence with Mechain.  Thus, we now have a M102 to seek out and study ourselves.  M102 lies around 40 million light years away from our galaxy.

 

Tracing a line NE from M102, through the stars Edasich (Iota Draconis), Eta Draconis and Aldhibah (Zeta Draconis). we come to a lovely planetary nebula, NGC6543, otherwise known as the Cat's Eye Nebula.  This object is +8.1 mag in brightness and very compact - some 0.4 x 0.3 arc minutes diameter.  As such it is relatively easy, even in small telescopes - though larger scopes will be needed to show its intricate internal structure.

 

The Cat's Eye Nebula, NGC6543 - Hubble Image.  Image Credit: NASA/ESA, Public Domain

The Cat's Eye is a greeny-blue in hue, a colour which is quite prominent even in smaller instruments.  It's often remarked that The Cat's Eye looks a little like the Outer Gas Giants, Uranus or Neptune.  What really marks NGC6543 as definitively not planetary is its central star.  This star is +11 mag and can be somewhat difficult to spot, due to the condensed and bright nature of the surrounding nebula.  Telescopic observation of the central star with averted vision reveals this nebula to be one of the so-called "blinking" planetaries - when moving one's vision from one part of the field to another, the nebula appears to blink on and off - disappearing from view. 

 

Higher magnifications with larger telescopes reveal the internal looped structure of the inner part of the nebula.  Observations by the Hubble Space Telescope have revealed much more than ground-based telescopes ever can: NGC6543 has several concentric shells of gas (see image above), which suggest a series of layers have lived off the surface of the central star, which in turn have been whipped into two 180 degree spaced jets, which give the nebula its somewhat oval shape.  It is theorised that these jets are actually a sign of an unseen secondary companion and represent the poles of its rotation. This cannot be confirmed as yet, but the Cat's Nebula gives astronomers the one of the best opportunities to study the dying phases of a star like our Sun.  NGC6543 lies around 3000 light years away from us and as such is one of our closest planetary nebulae - and also one of the youngest: observations suggest that it has been undergoing expansion and formation over the past 1000 years.

 

Moving South - by just over 24 degrees - through Rastaban, Beta Draconis, one of the four stars which represent Draco's head, across the border into Hercules, we come to one of the finest Globular Clusters in the sky, M92. 

 

Discovered in 1777 by Bode, Messier was to independently discover it and add it to his catalogue in 1781.  While it is somewhat overlooked in favour of the more illustrious M13 (more of which later), M92 is a spectacular object in its own right and can be found in binoculars and small telescopes easily. Under very dark conditions, it can actually be seen which the naked eye - at +6.44 mag it is just within theoretical naked eye visibility, though this must surely only be possible with averted vision.  It is well condensed as a target, being around 2 arc seconds in diameter, which helps keep its surface brightness up.  Binoculars of modest power will resolve the grainy texture of this globular extremely well - indeed, it is one of the best deep sky objects of its type for observation in binoculars. If the binocular view of M92 is excellent, then telescopically, M92 is spectacular.  Small telescopes will resolve the cluster into individual stars relatively easily, whereas larger scopes will really do it justice.

 

M92.  Image Credit: Mark Blundell.

Lying around 26,000 light years distance, M92 has a curious "part time" job - every 26,000 years, it becomes the marker for the Northern Celestial Pole.  Our Earth's precession, causing the polar shift, next brings the pole to within a degree of M92 in 16,000 CE. 

 

Those with larger telescopes may wish to try their luck with a much further globular cluster, NGC6229.  This cluster is much fainter than its neighbour and is to be found just under 7 degrees to the NW of M92.  This would be a similarly awesome sight as its neighbours, were it not for its distance - which is reckoned to be around 100,000 light years.  NGC6229 was discovered by Sir William Herschel in 1787 and was initially thought to be a planetary nebula. 19th century observations proved it to be broader in spectral signature and thus a collection of stars.  It will take a reasonably large scope to resolve NGC6229 into individual stars, but this will be a comparatively simpler task when imaging the object.

 

Whereas NGC6229 is really the preserve of larger instruments or imagers, the next object on our list for observing is quite simply for everyone - quite simply the finest globular cluster in the Northern Hemisphere, the wonderful M13.

 

M13 is within naked eye reach at +5.78 mag and was first noted by Sir Edmund Halley in 1714 as "a nebula [which] shows itself to the naked eye when the sky is serene and the Moon absent".  Messier himself logged it in his catalogue in 1764 and Sir William Herschel wrote of M13 "[it is] a most beautiful cluster of stars, exceedingly compressed in the middle and very rich."

 

M13's popularity is not solely down to its beauty - it's also exceptionally easy to locate, lying as it does in the "Keystone" of Hercules.  This central asterism of four stars, Zeta, Eta, Epsilon and Pi Herculis mark the Keystone, which represents the head of the Demigod.  M13 can be found 2 1/2 degrees to the South of Eta, following the Western side of the Keystone down to Zeta.  Once found, M13 will never be forgotten, as it is a marvellous object in both binoculars and any type of telescope.  Larger instruments will be able to resolve M13 easily into individual stars and give an observer the chance to spot the "Propellor" feature.  The Propellor is more easily seen in long duration photos and is common to a few globular clusters.  It is an area on the cluster in which a simple line of sight effect emphasises a lower density concentration of stars.  Human nature and cognition being what it is, this area is generally agreed to look like a three-bladed aircraft propellor, slightly silhouetted amongst the background stars.

 

M13. Image Credit: Mark Blundell.

The stars of M13 are very old, predominantly red stars, which have, in all probability, been gravitationally bound since just after the formation of the Milky Way itself.  Globular clusters in general are very metal poor, being so ancient - and the Iron content of the cluster on average is just 5% that of our Sun.  Our own Solar System, being barely more than a third of the age of M13 has benefitted immensely from the recycling of metals manufactured in the death throes of previous stars.  Our own Earth's core being part of this process, along with a very large amount of Iron that goes into our own physical makeup.  Any possible lifeforms which have evolved on planets around stars in clusters like M13 may well not have had access to metals in such abundance as life on our planet does, which would have required different biological strategies and processes to that which fuels a large amount of complex life on Earth.  These potential inhabitants of M13 would have an amazing night time sky though, as the heavens would be littered with hundreds (if not thousands) of stars brighter than the 1st magnitude - quite a view!  

 

At around 125 light years across, M13 is not the largest of our galaxy's Globular clusters (this prize must surely go to Omega Centauri), but nonetheless a very healthy size.  It is so prominent from our neck of the cosmic woods simply because it is relatively close, at around 25,000 light years away.  However, this is still not quite as nearby as Omega Centauri, which lies around 10,000 light years closer and the two closest Globulars, M4 in Scorpius and NGC6397 in Ara, both of which are found around 7,200 light years from us.   

 

If you're a seasoned observer, the arrival of M13 overhead in the Summer evening sky is a welcome return of an old friend.  If you're a beginner, this wonderful cluster awaits your discovery - it'll be an object you come back to time and time again, as it never disappoints.

 

The last of the objects on our wander around this area of sky is another Planetary nebula - NGC6210.  

 

At +8.8 mag and 0.3 x 0.2 arc minutes diameter, this nebula is similar in brightness and dimension to the Cat's Eye Nebula in Draco, though is somewhat less well-known.  This is a pity, as it's not a difficult object to pick up in small telescopes and rewards high magnification.  This nebula can be found 4 degrees to the NW of Kornephoros, Beta Herculis, which at +2.77 mag is the brightest star in Hercules . NGC6210 has, like the Cat's Eye, high surface brightness, due to its compact nature and this manifests itself in a beautiful blue coloration.  Like most planetary nebulae, this target is complimented greatly by observing it through an OIII filter, as the ionised Oxygen in its outer layers is easy to isolate and our mammalian eyes are most sensitive to greens and blues at low light levels.  The nebula shows itself to be a distorted oval shape, though larger telescopes of the 10-inch + class may well be able to distinguish a larger faintly glowing outer halo of gas, if conditions are favourable.  Like the Cat's Eye, NGC6210 has quite a complicated internal structure, which the Hubble Space Telescope's picture below aptly illustrates.

 

NGC6210 - HST Image.  Image Credit: NASA/ESA, Public Domain

NGC6210 was first discovered by the German-Danish Astronomer Friedrich Georg Wilhelm von Struve in 1825, while working at the observatory at the Imperial University of Dorpat in Russia.  Struve is best known for his immense work cataloguing double stars, many of which are still popularly referred to by their Struve classification.  Mysteriously, despite this area of sky being surveyed by Mechain, Messier, both William and John Herschel and numerous other experienced observers, it was Struve who first noted this relatively easy-to-spot planetary.  Although a challenge due to its diminutive size, NGC6210 is not a difficult target for anyone with a telescope - so why not have a go yourself?

Text: Kerin Smith