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 Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

The Monthly Sky Guide October 2017

 Late October is normally the month that finds those of us in the UK and Europe reverting to standard time (CET/GMT).  This is normally greeted with groans by those outside the astronomical community, as it leads to it getting darker earlier - those of us of a more astronomcial inclination will feel somewhat different, as it increases the opportunity for observations at a reasonable hour of the evening.  Those in North America will have to wait until the early part of November for this changeover to take place.  Naturally, what happens in the Northern Hemisphere has the opposite effect in the Southern.  Those in many territories in Australia and Brazil will begin their Daylight Saving Time (Summer Time) in October (New Zeland and Chile having started their DSTs somewhat earlier).

 Wherever you find yourself in the world, there's plenty going on in the skies above us this month...


The Solar System


The Moon


The Moon begins October at Waxing Gibbous phase, around 79% illuminated, in Capricornus. It reaches Full on October 5th in Pisces, rising around a quarter to six in the evening (from latitude 51 degrees N), and setting a little before 6.30am the following morning. This means inevitably, the first few days of October are not so great for deep sky observations or imaging with anything less than very narrowband filtration. 


The Moon reaches Last Quarter on the 12th, when high in the sky (from a Northern Hemisphere perspective) in Gemini. Beyond this point, the Moon presents on of its High Morning Crescent phases to those in the temperate Northern Hemisphere - a great time to observe the Moon's western limb, if you fancy getting up early. 


On the morning of the 17th, before dawn, the razor-thin old crescent Moon, some 6% illuminated, can be found above Mars and Venus in the east, which should make for a pretty wide field vista before the Sun rises. You may be able to find the Moon the following morning, slightly closer to Venus, but at just 2.4% illumination it may be a tricky spot. 


The Moon, Mars and Venus, Sunrise, 17th October.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

The Moon becomes New, the following day, October 19th, when it joins the Sun in the eastern half of Virgo. After this point in the month, the Moon becomes an evening object, joining Mercury and Jupiter low in the sky on the evening of the 20th. 


The Moon continues its journey through the southerly parts of the ecliptic, passing through Libra, Ophiuchus, Scorpius and Sagittarius, until reaching First Quarter in Capricornus on the 27th. 


The Moon ends the month in Aquarius, at 85% illuminated Waxing Gibbous phase. 



The Planets




The Innermost planet begins the month as a bright -1.3 mag morning target in Virgo. It is perilously close (just over 7 degrees) to the Sun, so despite the planet's luminosity, it's going to be a difficult spot in the dawn sky, sitting just over 5 degrees high at daybreak (from 51 degrees N).


Mercury is heading rapidly towards superior conjunction on October 9th, after which it will re-emerge as an evening planet, though won't be observable until the latter part of October. Even during the latter part of the month, Mercury will be really low on the western horizon for those of us observers in the temperate northern hemisphere - barely reaching a couple of degrees in altitude from 51 degrees N, although those further south in the equatorial regions of the Earth and the Southern Hemisphere will see it much better placed. 


Mercury at Superior Conjunction, Noon, 9th October.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

Mercury ends October at mag -0.4 in Libra. 





Venus, at -3.9 on the 1st, is still a great object to catch in the morning sky. At 91% illumination, our neighbouring planet sits 20 1/2 degrees high at sunrise (from 51 degrees N), making it straightforward to observe. 


On the morning of the 5th and 6th, Venus comes into very close conjunction with the much fainter Mars, separated by around 1/3 of a degree - easily putting both objects in the field of view of a telescope with a wide field, low power eyepiece and making binoculars observation of the event very simple. Mars at mag +1.8 and just 3.7 arc seconds across will be disappointing in comparison with the much brighter and larger Venus. 


Venus and Mars in Conjunction, Sunrise, October 6th. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

By mid-month, Venus has dipped a little in altitude at sunrise (just over 17 degrees high from 51 degrees N), but hasn't in brightness, remaining much the same as it was at the beginning of October. 


However, the trend as far as Venus is concerned is downward, as the planet slips towards the Sun. By the time October is at its end, Venus hasn't changed in brightness, but now stands just below 14 degrees high at daybreak  (again, from 51 degrees N). 





Mars starts October as a morning target in Leo. At +1.8 mag and just 3.7 arc seconds diameter, it is not an inspiring object to observe at the present time. Mars' proximity to the Sun, just under 23 degrees on the 1st, doesn't make it especially hard to find, especially with the brighter Venus nearby, but once located, the planet's small disk and comparatively low altitude in the sky make high magnification observations tricky. 


As previously mentioned, Mars and the much brighter Venus are in close conjunction on the morning of the 5th and 6th which will be an interesting sight to behold in telescopes and binoculars. This line of sight meeting of the two worlds doesn't mean they are actually in close proximity within the solar system at all.  Venus is at 226.4 million km distance, whereas Mars is 379.5 million km away. 


By the middle of the month, nothing has changed much as far as Mars is concerned. The planet's brightness, altitude at sunrise and size hasn't changed significantly. 


By October's end, Mars stands just over 26 degrees high at sunrise, still at +1.8 mag and now presents a 3.9 arc second diameter disk. 





Jupiter begins October as a difficult evening object for those of us in temperate northern climes, as although bright at -1.7 mag, it is very low (just over 5 degrees) at sunset (from 51 degrees N). 


Jupiter is heading for superior conjunction on the 26th October, after which it will re-emerge from the other side of the Sun (from our perspective here on Earth) as a morning planet. 


 Jupiter at Superior COnjunction, 26th October.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,



The Ringed Planet is an excellent evening object in early October. Though low in the south of the sky from a northern hemisphere perspective, Saturn always presents a pleasing view in a telescope, though those in the Southern Hemisphere will see it undeniably better. 


At +0.5 mag and 16.1 arc seconds across on the 1st, Saturn is hardly striking from a naked eye perspective, but is still brighter than any star in the same area of sky - in this case the Ophiuchus/Sagittarius area. 


By mid-month, Saturn is still much the same size and brightness and now sets a little shy of three hours after the Sun (from 51 degrees N). 


Saturn at Sunset, Ocober 15th.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,


At the end of October, Saturn is still +0.5 mag and now sets around 2 1/2 hours after the Sun. The window for observation is slowly closing - so make the most of Saturn while you can. 


Uranus and Neptune 


Whereas Neptune came to opposition last month and was therefore the focus of our attention, this month it's the turn of Uranus to come to the fore. 


Uranus comes to opposition in Pisces on October 19th and presents a +5.7 mag, 3.7 arc second diameter disk for much of the month. Unlike many of the inner planets, the two outer gas giants don't vary tremendously in brightness, even around opposition. It's certainly possible to see Uranus with the naked eye from a dark site, but binoculars or a telescope are often a necessity for positive identification of this distant world. And distant it is - even on the night of opposition, Uranus lies a staggering 2.83 Billion Km away. Even traveling at around 186,000 miles per second, light from Uranus takes 157 minutes to arrive at this opposition.  


Uranus in Pisces, Opposition night.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

Neptune is just past opposition in September, so is still well-situated for observation throughout the majority of the hours of darkness in October. At +7.8 mag and just 2.3 arc seconds across, it is considerably more challenging to find - though can be relatively easily. Neptune lies about half a degree to the SE of the star Hydor, or Lambda Aquarii, a 3.75 magnitude target. Hydor is one of the five stars which make up the main "body" of Aquarius. Although none of these stars are brighter than the third magnitude, it is reasonably simple to make these out from a reasonably dark location. Neptune can be found inside this distorted pentagon of stars, closest to Hydor. Binoculars will be needed to make a positive identification, as Neptune is below naked eye visibility - though a telescope with high magnification will be needed to see the planet's tiny disk. 


Neptune in Aquarius, October 15th.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

On the nights of the 3rd and 31st October, the Waxing Gibbous Moon visits this part of the sky, providing a useful celestial signpost to Neptune's location - just after midnight, on both nights, the Moon will lie around 1 1/2 degrees to the SE if Neptune. 





Comet C/2017 O1 (ASASSN) is well placed for observation during October, travelling north through the stars of Perseus, becoming circumpolar (from 51 degrees N) on the evening of the 2nd. The comet crosses the northern border of Perseus, into the faint constellation Camelopardalis (the Giraffe) around 16th October.  The comet may be approaching the limits of naked eye visibility (from a very good location), but as most readers know, cometary prediction is a difficult art. It seems as if C/2017 O1 was found undergoing an outburst, which may have boosted its initial brightness somewhat. However, most recent observations (at time of writing), but the comet towards the upper range of brightness estimates. At worst, C/2017 O1 should still be a binocular object and worth looking out for. 


Comet ASSASN - location shown for 15th October.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars, 



The Orionid meteor shower peaks on October 21st this year. While not as major a shower as the Perseids of August, or the Geminids of December, the Orionids normally put on a reasonable show. With the Moon just past New on the night of the peak, observers should be able to see a few of the 10-20 meteors per hour which will be caused by particles arriving from the debris field left over from the path of the most famous of all comets, Comet Halley. With the Moon out of the way, this should be a great time to observe this particular shower. 



Deep Sky Delights in Pegasus and Aquarius 


Pegasus and Aquarius.  Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

Moving in a southerly direction from last month’s Deep Sky highlights in Cepheus and Cassiopeia, we come to the constellations of Pegasus and Aquarius, which share a border and are home to some easy and not-so-easy to observe objects. 

Though lacking in major nebulae, Pegasus is a haven for galaxies - maybe not quite to the extent of the Virgo and Leo regions - but has many extra-galactic targets worth attention. 


The most famous feature of Pegasus is readily observable without a telescope - this is, of course, the famous Square of Pegasus. Consisting of the stars Alpheratz (Arabic for “the navel”), Scheat (”the leg”), Algenib (”the flank”), Markab (”the saddle”), the Square of Pegasus dominates this area of sky and can be used as a useful “jumping off” guide for starhopping. However, the Square of Pegasus is not solely “of Pegasus”, as Alpheratz is actually now officially a part of neighbouring Andromeda. This is a similar situation to Elnath (Beta Tauri) which is officially now part of Taurus, but has been shared as Gamma Aurigae with neighbouring Auriga. These constellations are rare as they are still shown on modern star charts as connected via their “shared” star. 


A third of the way along the line between the lower stars of the Square, Markab and Algenib, lies an object not visible to the naked eye at all. This is the notable (if unspectacular) Pegasus Dwarf Galaxy, This is an associated galaxy with the nearby M31, the Andromeda Spiral and as such a neighbour of our own Milky Way. It’s a rather faint object at +13.2 mag and spread out over a reasonable area of sky, so is only really detectable in long duration photos. Dwarf galaxies are often (though not always) older, more primitive than galaxies such as our own. However, whilst they are not brilliant in the conventional visual sense, dwarf galaxies such as the Pegasus Dwarf are havens for Dark Matter. The Pegasus Dwarf lies 3 million light years away from the Milky Way and is tidally interactive with M31. 


Much more easily-observed and better-known is an object on the other side of Pegasus: the great globular cluster, M15. Found 4 degrees north-east of the star Enif (Arabic for “nose”), or Epsilon Pegasi, M15 is a glorious object in any telescope or binoculars and at +6.2 mag can be seen as a naked eye object from a reasonable site. This globular was discovered by Maraldi in September 1746 and catalogued 18 years later by Messier in 1764. Located about 33600 light years away, M15 contains around 100,000 stars. As a well-known object, it has been studied exhaustively and found to contain the first extra-galactic planetary nebula discovered: Pease 1, first identified in 1928. In addition to Pease 1, M15 has a pair of co-orbiting neutron stars, 8 pulsars and two strong X-ray sources. It has been postulated that one of these sources is in fact a Black Hole, to which has been attributed M15’s relatively recent core collapse. Globular clusters are both beautiful and intriguing objects and M15 is almost certain to contain more as-yet-undiscovered features. 


M15, pictured by the Hubble Space Telescope (showing Pease 1, upper left centre). Image Credit: NASA/ESA, Public Domain.

Back inside the Square of Pegasus lies the lovely NGC7814 - the “Little Sombrero” (so called because it resembles the Sombrero Galaxy, M104, in Virgo). NGC7814 is a Spiral, presented edge-on to our line of sight. This reveals a dark dust lane bisecting a bright core. At +10.6 mag this galaxy isn’t overly bright, but due to its compact nature, is still well-seen in small telescopes. NGC7814 is easily found due to its proximity to Algenib. 


NGC7814.  Image Credit: Hunter Wilson, Creative Commons.


Another galaxy near to a member of The Square is NGC7479, which lies just under 3 degrees south of Markab. This is one of the most photogenic Barred Spirals in the sky, lying almost face on to us. It was discovered in 1784 by William Herschel and is just slightly fainter than 7814 at +10.9 mag. NGC7479 is a very active galaxy - a so-called Seifert Type, in which enormous amounts of star formation are taking place. The serpentine structure of NGC7479 is beautifully depicted in long-duration photos - it almost seems to be slithering like a Sidewinder through space! 


NGC7479, pictured by the Hubble Space Telescope. Image Credit: NASA/ESA, Public Domain.

Further north are a fascinating collection of galaxies: the NGC7331 group and Stephan’s Quintet. These two groups of galaxies are separated by just half a degree of sky and can be found north of Matar (Eta Pegasi). Of the two groups, the NGC7331 group are the more conspicuous and their principle member was discovered first - by William Herschel - in 1784. This principle galaxy, NGC7331, was thought to be a very similar size, mass and taxonomy to our own Milky Way: a tightly-barred spiral. However, most up-to-date surveys of the Milky Way suggest that it may only have two massive spiral arms, whereas NGC7331 has more (NGC6744 in Pavo is now seen to be the nearest Milky Way analogue). Behind NGC7331 lie NGCs 7340, 7336, 7335, 7327 and 7338 - some of which can be seen with averted vision in reasonable-size telescopes. NGC7331 at +9.5 mag is by far and away the most prominent of the group and can be seen in smaller scopes. The whole group is a great target for astrophotography as regular contributor Mark Blundell’s picture below clearly shows. 


NGC7331 and Stephan's Quintet.  Image Credit: Mark Blundell.

The second of these two galaxy groups is the famous Stephan’s Quintet. Discovered in 1877 at Marseilles Observatory by Eduoard Stephan, the Quintet consists of NGCs 7317, 7318, 7318A, 7318B, 7319 and 7320 (this is technically a Sextet as 7318A and B are separate galaxial cores). Stephan’s Quintet occupies a tiny area of 3.5‘ x 3.5’ of sky and is an area of both enormous destruction, as the component galaxies literally rip each other apart and massive areas of creation where the resulting gas-rich loops of material released by these dynamics leads to starbirth. 


The interior of Stephan's Quintet, pictured by the Hubble Space Telescope. Image Credit: NASA/ESA, Public Domain.

Of the components of the Quintet, NGC7320 appears to be an unrelated foreground object - much closer to us at 39 million light years distance as opposed to the 210-350 million light years of the other members. 


Moving south into the Zodiacal constellation of Aquarius, the Water Carrier, we are presented with a large, but quite a barren area of sky. Although Aquarius is rather muted in terms of brighter stars, it is a haven for deep sky objects. The most northerly of these is the very fine globular cluster M2. At +6.46 mag, it is amongst the brighter of these interesting objects, lying 37,500 light years away from us and about 175 light years in diameter. From Earth, it appears 2.1 arc minutes in diameter, M2 is about the same relative size and brightness of the neighbouring M15 and the second of Hercules’ well-known globulars, M92. Discovered by Comet Hunter Jean-Dominique Maraldi in 1746, it languished in relative obscurity until Messier added it to his list in 1760, describing it as a “Nebula without stars”. Modern instruments show it as most definitely “with stars”, indeed there are several beautiful star chains visible through telescopes, as well as some deep, dark lanes and patches, adding to the “three-dimensionality” of the object, particularly in larger telescopes. There are quite a mix of older orange and newer blue stars within M2, making it a particularly pretty telescopic sight. 


M2, pictured by the Hubble Space Telescope. Image Credit: NASA/ESA, Public Domain.

Moving SW from M2, we arrive at three objects in quick succession: NGC 7009, The Saturn Nebula, the asterism M73 and another globular, M72. The Saturn Nebula is a fascination Planetary Nebula, well worth seeking out in any telescope, as it is reasonably bright, at +7.8 mag, yet compact at 0.5 arc minutes across. Telescopes of 6-8-inch aperture will be needed in order to see the two extended lobes that give the object its popular name. Lord Rosse, observing NGC 7009 in 1850, described two lobes or projections sitting either side of the nebula, making it appear very similar to Saturn, when its rings are edge on to us. Although the object has a distinctly un-Saturn-like green-blue hue, which is most easily seen in long duration photographs. The Saturn Nebula, in common with some other Planetaries - including the Blinking Planetary - can appear to blink on and o when looking at it for prolonged periods. This is of course a trick of the eye, caused by NGC 7009’s reasonably bright central star overwhelming a dark-adapted observers eye. When the observer averts their vision slightly, the Saturn Nebula returns to view. Although the Blinking Planetary is the most well-known object that exhibits this phenomenon, to the writer’s mind, the Saturn Nebula is actually the best example of a “Blinking” Planetary Nebula. As ever, aperture helps in resolving the finer details of NGC 7009 (especially the projections), but the Saturn Nebula should be sought out by all those with telescopes - it’s certainly bright enough to be seen in even the smallest scopes. 


Saturn Nebula, pictured by the Hubble Space Telescope. Image Credit: NASA/ESA, Public Domain.

The next object is an interesting one. When is a star cluster not a star cluster? Answer: when it’s an Asterism like M73. Lying less than 2 degrees SW of the Saturn Nebula, M73 has been the subject of some controversy over the years since its discovery. Charles Messier first noted it in 1780 as a “cluster of four stars with nebulosity”, although this nebulosity has never been picked up by any other observers. John Herschel, whilst including it in his General Catalogue, was suspicious of its definition as a true cluster. Debate raged on throughout the 20th century as to the true nature of the Y-shaped M73, with evidence of a relationship between the members of the group being published for and against. The matter was finally and conclusively put to bed in 2002, when spectral signatures of each of the constituent members, gathered in high resolution, concluded that they were all moving in different directions and the cluster was not, it fact, a cluster. M73 is not unique amongst the Messier list for controversial description, but remains interesting for the fact that it took so long to finally work out its true nature. 


1.5 degrees to the west of M73 is the slightly less controversial Globular Cluster M72. At +9.27 mag, it is considerably fainter than M2, despite being not much smaller. M72 is considerably further away from us than M2 - it lies 55,000 light years distance from Earth. As it is fainter and further away, M72 requires a larger telescope to resolve individual stars. It is a pleasing sight in a 10-inch reflector and above, though William Herschel in his observing notes of 1783, noted that a power of 150x was needed to resolve the individual stars “fairly”. 


M72, pictured by the Hubble Space Telescope. Image Credit: NASA/ESA, Public Domain.

Lastly, we journey 23 degrees east of NGC 7252, to rendezvous with the closest Planetary Nebula to Earth, NGC 7293 - The Helix Nebula. Overlooked by experienced observers, such as Messier and William Herschel, it is not di cult to understand why. Though intrinsically quite bright at +7.59 mag, the Helix is half the diameter of the Full Moon, which spreads its surface brightness out considerably. The Helix was eventually discovered around 1824 by German Astronomer Karl Ludwig Harding. Observation or the Helix requires either large binoculars and a very dark site, or a wide eld low power eyepiece and as much telescopic aperture as you can throw at it! Large Dobs are the ideal instrument for observing the Helix, particularly when coupled with an OIII filter. From our perspective on Earth, we see the Helix like looking down a tube. Its prolate spheroid shape is almost aligned on axis with us, at a distance of 650 light years. 2.5 Light years across, the Helix appears 14.7 arc minutes across at its widest point. A magnificent object, it will take the right conditions to see it well - if the Moon’s up, you’ll have to wait until it has set before attempting to locate the Helix. It will be well worth the wait though. 

 The Helix Nebula, pictured by the Hubble Space Telescope. Image Credit: NASA/ESA, Public Domain. 

Text: Kerin Smith