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Telescope House June Sky Guide Part 2


Comets


There are no really bright comets visible at present.  However both comets C/2020 T2 (Palomar) and the periodic comet 7/P Pons-Winnecke are visible in telescopes and large binoculars.  At around 10th magnitude, both objects will be visible in very different parts of the night.  C/2020 T2 can be found tracking south through Bootes during June and will be visible for much of the night. 




C/2020 T2 (Palomar) path through Bootes, June (comet position shown 1st June).  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.



Pons-Winnecke will not rise until 1am in Capricornus and will track south through neighbouring Aquarius and further south into Pisces Austrinus during the latter part of June, making it difficult for observations in the northern hemisphere.




Comet Pons-Winnecke path through Capricornus, Aquarius and Piscis Austrimus, June (comet position shown 1st June).  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.



Meteors


There are no major meteor events in June, though being out under clear skies, there is always the chance of observing a sporadic meteor or two during the night.  The next shower to be on looking out for are the Southern Delta Aquariids in late July/early August.




Noctilucent Clouds 


Noctilucent Clouds are often seen in June - their bright gossamer/web-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. Interestingly, a significant link between the power of the Northern Polar Stratospheric Vortex and the production of NLCs in the Southern Polar Mesosphere (the atmospheric layer above the Stratosphere) has been found by analysis of ground based data and that gleaned form NASA climate satellites.  It would appear that when the Northern Polar Vortex is particularly strong, this negatively affects the production of NLCs over the Southern pole over 12,000 miles away.  These interconnections are a sure sign of how little we truly understand the mechanics of the atmosphere of our home planet and how much is still potentially to be uncovered.


Whatever their origins, now is the best time to see NLCs from Northern latitudes.  Interestingly, whilst Noctilucent Clouds have been observed in the Southern Hemisphere, their incidence appears much fewer than their Northern Hemispherical counterparts. 



A spectacular NLC display captured by Bresser's Anke Morbitzer.  Check out Anke's other pictures of the sky and atmospherics at http://astroyuki.com.  Image used with kind permission.


Click here for Anke's timelapse video of an LNC display from 2020


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 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.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.




M102 - Hubble Space Telescope Image (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 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.



 

NGC6543, The Cat's Eye Nebula - Hubble Space Telescope Image (NASA/ESA).  Public Domain.



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 by Mark Blundell.  Image used with kind permission.



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.



 

NGC6229 - Sloan Digital Sky Survey Image.  Creative Commons. 



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 by Mark Blundell.  Image used with kind permission.



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 - Hubble Space Telescope Image (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?



Original text: Kerin Smith

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