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Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 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.

 

 

The Solar System

 

Moon

 

The Moon begins June on the Cetus/Aries borders as a Waning Crescent of around 6% illumination. You could catch the Moon in the predawn sky, sitting a little to the west of the striking Venus, on the morning of the 1st, were it not for the fact that both Venus and the Moon are rising practically in line with the Sun from a northern hemisphere perspective. Those in the equatorial regions of the planet will fare better in this respect, as the Moon is still 28 degrees away from the Sun at this point.

 

New Moon occurs three days later, when the Moon slides to the south of the Sun in Taurus, after which it becomes an evening object. 

 

We are now past the point where the Moon is at its greatest separation from the horizon for northern hemisphere observers, in relation to the Sun’s position in a more southerly part of the Ecliptic.  As such, the High Spring Crescents are now over for Northern hemisphere observers for another year.  Now the Sun is in the northern hemisphere of the sky, the altitudinal difference between the two bodies, as viewed from temperate or high northern hemisphere perspectives, during the New-to-Half-Phase sector or the Moon’s monthly trip round the sky, is less extreme.  As a result, the altitude of the 7 day old moon above the horizon on the 9th June at sunset, is still a healthy 39 1/2 degrees (from 51 degrees N).  Wind the clock back to May’s seven day old Moon and you would find it over 12 degrees higher in the sky at sunset from the same latitude. Wind back further still and April’s 7 day old Moon stood an impressive 59 degrees high at sunset (again, from 51 degrees N).

 

The Moon reaches First Quarter in the 10th while in Virgo, sitting almost equidistant between Virgo’s principal star Spica and Regulus, or Alpha Leonis, the brightest star in neighbouring Leo.

 

The Moon then gently continues its slide south through the ecliptic, until it reaches Full in the Ophiuchus/Sagittarius borders on the 17th, when it will be found under 3 degrees from neighbouring Jupiter, as both bodies rise in the early morning sky.   On the morning of the 19th, the Moon can be found just under a degree and half from Saturn in Sagittarius.

 

Full Moon and Jupiter in Ophiuchus, 17th June.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

The Moon comes to Last Quarter on the Pisces/Aquarius borders on 25th June, before ending the month much as it started, on the 30th as a thin 9% illuminated Crescent in Taurus, rising just next to the Hyades, a little under a hour and three quarters before the Sun rises.  We’d normally point out that the Moon’s being close to New phase at beginning and end of the month would favour deep sky observers and imagers during these periods. But as June coincides with the Sun’s northern hemispherical Summer Solstice, true astronomical darkness won’t return until late July for those around 51 degrees N latitude - and later still for those based further north.  Of course the reverse is the case for readers in the Southern Hemisphere, who will be experiencing their midwinter at this time.  This isn’t to say observations and imaging can’t take place at all, but that true astronomical darkness inevitably produces the best contrast between a target and the background sky - essential for resolving fainter detail.

 

 

Mercury

 

The Innermost Planet starts the month in Taurus as an evening object, standing just over 9 degrees high in the NW (from 51 degrees N). From a temperate northern hemisphere perspective, this evening apparition of Mercury will be probably the best chance of the year to observe the illusive inner planet, as it is now approaching the most northerly part of the Ecliptic. At -1.1 magnitude and 5.5 arc seconds across, Mercury presents an 82% illuminated face at the beginning of the month.  It is separated from the Sun by just over 13 1/4 degrees on the 1st.

 

As May progresses, Mercury heads westwards away from the Sun, increasing in angular size, but decreasing in brightness, as its phase shrinks as it pulls towards us within its orbit. By the 7th, Mercury will be -0.5 mag and showing 71.5% phase across a 6 arc second diameter disk. It will stand over 12 degrees high above the horizon at sunset on the evening of the 7th (from 51 degrees N), separated from the Sun by just under 18 3/4 degrees.

 

By mid-month, Mercury is nearly at half phase, shining at a steady +0.0 mag, having increased its angular diameter to 7 arc seconds.  By this point it will be separated from the Sun by nearly 23 1/2 degrees and stands just under 13 1/2 degrees high at sunset (from 51 degrees N). 

 

On the 18th June, Mercury comes into very close conjunction with Mars, with both bodies appearing just 13 arc minutes from each other in Gemini.  Mercury will be +0.2 mag at this point and appear 13 1/2 degrees high at sunset.  Mars, however, will be over a magnitude and a half fainter at +1.8 mag and will be a significantly more difficult target to spot in the twilight sky. This conjunction will require a telescope and very favourable atmospheric conditions to spot, though won’t be an exceptional sight, as Mars is now a tiny 3.7 arc second diameter target - half the diameter of Mercury, which is now 7.4 arc seconds across.

 

Mercuy in conjunction with Mars, Sunset, June 18th.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

Mercury reaches its maximum eastern elongation from the Sun on the 24th June. By this time it will be a +0.6 mag target, displaying a 8.3 arc second diameter, 38% illuminated disk.  At this point in the month it will be separated from the Sun by over 25 degrees.  Mercury will stand just under 12 degrees high at sunset (from 51 degrees N) on the evening of the 24th.

 

Mercury ends this pretty spectacular month on the 30th in Cancer, having faded significantly from peak brightness earlier in June to a modest +1.1 mag.  It will now be a relatively thin 27% illuminated crescent of 9.3 arc seconds diameter.

 

 

Venus

 

Venus begins the month in Aries.  A morning object, rising at a little after 4am on the 1st, our nearest planetary neighbour is not well placed for observation from the temperate northern hemisphere (or further north). However, it will be much better placed for those in the equatorial regions of our planet, as Venus’ separation from the Sun is still a fairly healthy 20 degrees at the month’s beginning.

 

Venus alongside the old crescent Moon, sunrise, 1st June.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

As Venus is rising practically in line with the Sun, it will stand just 6 degrees high from the horizon at sunrise (from 51 degrees N), shining at a brilliant -3.9 mag.  It will certainly be possible to see Venus from European and North American locations, if the atmosphere is kind and your eastern horizon is flat enough.  However, the view through a telescope will not be great at all - atmospheric extinction and sheer air mass and movement will play havoc with seeing at even modest telescopic magnifications, so we would thoroughly recommend other more rewarding targets at this time.

 

Venus is headed sunward, towards Superior Conjunction in mid-August, so the trend as far as observational possibilities go, gets worse as the month progresses.  Venus ends June just under 12 1/4 degrees from the Sun.  Lovely as Venus can often be, now is not the greatest time to see it.

 

 

Mars

 

The Red Planet is technically observable in the evening sky as the month begins, but at +1.8 mag, just 3.9 arc seconds diameter and an altitude of a little below 19 degrees at sunset (from 51 degrees N) on the 1st, is a poor target.  Like Venus, Mars is headed sunwards, albeit at a more sedate pace.  Superior Conjunction occurs in early September, so while there’s still time to catch Mars, again, as with Venus, there’s little point at the current time.  The very patient and talented planetary astrophotographer could potentially still image Mars at this time and catch some major surface details on its tiny face, but the visual view will be beset with disappointment.  Mars sets around 2 1/2 hours after the Sun on the 1st, being separated from it by 29 degrees.

 

Mars at sunset, 1st June.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

By the end of June, the Martian situation has deteriorated further - Mars is still +1.8 mag, though has shrunk to 3.7 arc seconds diameter.  It now stands just under 10 degrees high at sunset (from 51 degrees N) and sets just over an hour and a quarter later.  To all intents and purposes, the long window of evening opportunities to observe Mars has now come to an end.

 

 

Jupiter

 

Whereas Venus and Mars are disappointments, Jupiter is anything but, reaching Opposition in Ophiuchus in the first half of the month.  Rising at a little after 9.30pm (from 51 degrees N) in the evening of the 1st, Jupiter will shine at a prominent -2.6 mag brightness, offering up a 45.9 arc second diameter disk.  Jupiter reaches transit point (the highest point in the sky) at just after twenty to two the following morning, standing over 16 degrees high in the south as it does (from 51 degrees N).  

 

Jupiter reaches Opposition with Earth on the 10th June.  By this point it will not be any brighter than at the month’s beginning, have increased its angular size by just 0.1 arc seconds - hardly a major gain.  Transiting at just after 1am, Jupiter will, at this point, be 641 million km / 398 million miles from Earth.   As far as Oppositions go, this is a fairly average one.  Jupiter can get closer and subsequently appear larger and fractionally brighter than it appears currently. The following couple of Jovian Oppositions to this one will be closer and brighter as a consequence. 

 

Jupiter at transit point, opposition night, 10th June.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

By mid-month, Jupiter will rise just after half past eight in the evening and transit at twenty to one the following morning. 

 

By June’s conclusion, Jupiter rises at just before half past seven in the evening, transiting four hours later. Still shining at -2.6 mag, the planet will remain bright and unmistakable in the SE in the early evening for some months to come.

 

Jupiter, 1am 21st June - simultaneous GRS and Io transit and shadow transit.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

It’s worth pointing out again that for those readers in the northern hemisphere, Jupiter is not especially well-placed, reaching a maximum altitude of 16 1/2 degrees at the end of the month (from 51 degrees N).  Those attempting observations are encouraged to keep magnifications modest when it comes to telescopic viewing. Atmospheric haze and movement will inevitably be something we’ll have to deal with and those attempting to image Jupiter would be best to go down the high speed filming route, preferably using an Atmospheric Dispersion Corrector, which can compensate for atmospheric refraction, which affect objects increasingly, the closer they appear to the horizon. An ADC won’t combat poor seeing, but it will make a difference in keeping everything tighter from a spectral point of view, as is aptly displayed by Geof Lewis' image of Jupiter below, taken around last year's opposition. 

 

 Image credit: Geof Lewis.  Image used by kind permission.

 

 

Saturn 

 

The Ringed Planet is coming to Opposition next month and can be found to the east of Jupiter in neighbouring Sagittarius. At +0.3 mag, at the beginning of June it’s nowhere near as prominent as Jupiter, but easy enough to find, being brighter than any star in its immediate area of sky. Saturn presents an 18 arc second diameter disk at the start of the month. 

 

Saturn being further east in the ecliptic, rises later than its planetary neighbour, breaching the horizon at a little after twenty to midnight on the 1st and reaching transit in the south at just before 4am, when it reaches an elevation of 17 degrees above the horizon (from 51 degrees N).

 

By mid-month, Saturn will rise at 11.40pm and transits at 2.45am the following morning (from 51 degrees N). It will have increased brightness by an almost undetectable tenth of a magnitude from the month’s beginning and increased its diameter to 18.2 arc seconds across. 

 Saturn and major moons, 15th June.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

By month’s end, Saturn will rise at a little after 9.30pm and transit at 1.42am. By this time Saturn will again have become fractionally brighter and now shines at +0.1 mag, presenting a 18.4 arc seconds diameter disk. 

 

 

Uranus and Neptune 

 

Uranus is in Aries and rises just under an hour and a half before the Sun on the 1st.  At +5.9 magnitude and having reached a maximum altitude of just over 12 degrees high  as the Sun rises (from 51 degrees N), it won’t be practical to attempt observations of the planet at this time, as the bright morning sky will wash out such a faint target.  Uranus is separated from the Sun by around 35 degrees at the month’s beginning.  By the end of June, this figure has increased to 62 degrees and the planet now stands just under 30 degrees high in the east at sunrise (again, from 51 degrees N).  If it wasn’t for permanent astronomical twilight at this time of year, it would now be a more practical task to attempt to find Uranus in the morning sky.  It will still be a month or two before circumstances come together and Uranus becomes a comparatively easier target.

 

Neptune, further west in the ecliptic than Uranus, rises earlier than its neighbour (a little after 2am on the 1st), in the constellation of Aquarius.  Although separation from the Sun is distinctly healthier than Uranus’, Neptune is much fainter and always a greater challenge to readily identify.  At +7.9 mag and just 2.3 arc seconds across, it is difficult at best. Again, the lack of true astronomical darkness will come into play when trying to seek out Neptune in the early morning sky.

 

Uranus and Neptune relative positions, 15th June.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

The latter half of the year will be when both the outer planets rise earlier and also reach opposition - this occurs in late October for Uranus and early September for Neptune.  This will be an easier and more productive time to try and find these outlying worlds.

 

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.

A fine display of Noctilucent clouds taken by Anke Morbitzer of Bresser GMBH in 2018.  Image used with kind permission.

 

 

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