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The nights are colder but longer; explore the early winter sky with:

The Australian Night Sky - June 2017

By Wayne Roberts

What's In The Sky This Month

The Planets

Our Monthly Feature

 

[Click here to show or hide the explanatory notes]
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What's in the sky this month; June 2017:

 1st Regulus (Alpha [α] Leonis, magnitude 1.3) occulted by Moon (not from Australia);
     First Quarter Moon.
 3rd Venus at greatest elongation west (of the Sun), 46°.
 6th Dwarf planet Ceres in conjunction with the Sun.
 9th Moon at apogee (farthest from Earth, 406,401 km);
     Full moon (406,272 km distant, the farthest Full Moon for 2017).
10th Theta Ophiuchids meteor shower peaks;
     Jupiter stationary (ends retrograde motion).
12th Venus at aphelion (farthest from Sun, 108.9 million km/0.7282 au). 15th Saturn at opposition.
16th Neptune occulted by Moon (not from Australia).
17th Neptune stationary (begins retrograde motion);
     Last Quarter Moon.
19th Mercury at perihelion (closest to Sun, 46.00 million km/0.3075 au).
21st Earth at winter solstice (summer solstice in the northern hemisphere).
22nd Mercury in superior conjunction (passes behind Sun from our perspective, midnight 21st/22nd).
23rd Aldebaran (Alpha [α] Tauri, magnitude 0.8) occulted by Moon (not from Australia);
     Moon at perigee (closest to Earth, 357,937 km).
24th New Moon.
27th June Bootids meteor shower peaks.
28th Regulus occulted by Moon (for the second time this month; again, not from Australia).

N.B.: When reading the following, refer back to the explanatory notes at the beginning of this article (click on the above link to expand) for information on terminology, angular separation approximations and adjustment of latitude & longitude.

Two meteor showers peak in June, the Theta [θ] Ophiuchids on the 10th and the June Bootids on the 27th. The former has only been referred to by this title since the early 1960’s; it was previously known as the Scorpiids/Sagittariids, Alpha Scorpiids or Delta [δ] Sagittariids. The radiant is variable and ill-defined over a large area, but is centred about halfway between Alpha Scorpii (Antares) and Delta Sagittarii. Theta Ophiuchi is the brightest star (only moderately so, at magnitude 3.25) in that locale, thus explaining both the previous and current names for the shower. The astronomical software used in compilation of these viewing notes does not plot this shower, so the transit time of the radiant is best given as that for Theta Oph, 12:31 am on the 10th.

While the British Astronomical Association lists the ZHR as 10, this would appear to be optimistic, about twice what would usually be expected. Unfortunately, the Full Moon sits just 7° from Theta Oph in the early morning hours of the 10th, so while the radiant is high in the sky, this event is severely compromised from the start.

The June Bootids – the ‘June’ tag is presumably attached to differentiate this shower from the Quadrantids (peaking in January; the name comes from a defunct constellation), which also emanate from the constellation Bootes – are predicted, by the International Meteor Organization, to peak at 7 pm on the evening of the 27th. This gels well with the radiant of this predominantly northern hemisphere shower, which is only above our northern horizon from 6:43 pm until 11:04 pm. While the predawn hours are normally best suited for viewing meteor showers, the afore-mentioned times would seem to delineate the preferred window, especially as evening twilight fully fades at 6:44 pm and the 15% illuminated waxing crescent Moon sets at 8:49 pm, five minutes before the radiant reaches its very modest peak altitude of 4½°.

Showers seen in 1916/21/27 were attributed to the Bootids, which arise from debris scattered by Comet 7P/Pons-Winnecke. No further activity was recorded until 1998 when ZHR’s as much as 100 were recorded, followed by counts of up to 50 in 2004 and less than 10 in 2010, with no activity in other years. No outbursts are expected this year but with favourable conditions and the fickle unpredictable nature of meteor showers, it’s worth a look.

The following chart is configured for 7:00 pm on the 27th, and labels the position of the radiant at that time; the three stars mentioned in relation to the Theta Ophiuchids are also labelled.

As shown in the monthly summary above, the Moon occults Regulus twice this month, and Aldebaran once, but none of the events, unfortunately, will be served up to we in Australia. Regulus is occulted from our location on the 1st, between 3:04 am and 3:46 am, but 45°-52° below our western horizon, the star having been 2° above the horizon when the Moon set at 11:06 pm. The event of the 28th is even less favourable for us; the Moon’s limb misses the star by almost ½°, closest approach occurring at 9:41 am, 12° below our eastern horizon.

The pairing of Luna and Aldebaran on the 23rd is every bit as unaccommodating, closest approach of a little over ½° takes place more than 60° below the NE horizon at 12:08 am.

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THE PLANETS

Mercury

The Messenger of the Gods spends the first three weeks of June in the latter stages of its best morning apparition of 2017, and the remainder climbing away from the western horizon as it begins its best evening apparition of the year.

On June 1st, Mercury rises at 5:39 am, just under ¼ hour before morning twilight commences at 5:53 am, and has attained an altitude of 18° in the NE by the time the Sun rises at 7:26 am. The planet’s disk spans 6.3" [" denotes arc-second = 1/60th of an arc-minute (symbol ') or 1/3600th of a degree (symbol °)], is 66% illuminated and shines brightly at magnitude -0.3.

After reaching perihelion – its closest approach to the Sun along its orbital track – on the 19th, the planet rounds the far side of Sol from our perspective (termed superior conjunction) at midnight on the 21st/22nd, thereafter appearing in our evening skies. On Saturday 24th, which will serve as our designated viewing night this month as it coincides with New Moon, Mercury is still in close proximity to the sunset horizon, and far too close to the Sun for observation. It sets at 5:17 pm, having been at an altitude of only 1° at sunset eight minutes earlier; the span of the 99% lit disk stands at 5.1" and shines vigorously, albeit unseen so close to our local star, at magnitude -1.9.

Come the end of the month, Mercury has started to pull away from the horizon, albeit still well within twilight – it sits 6° clear of the NW horizon at sunset (5:11 pm) and sets itself at 5:52 pm; the span of the disk is out to 5.2", with phase and brightness down to 92% and magnitude -1.2.

Save your viewing aspirations until July and August when the normally elusive innermost planet hangs prominently in the evening skies.

Beginning the month in Aries, Mercury moves into Taurus on the 3rd, and then Gemini, where it sees out the month, on the 22nd (it’s a pity that it’s unobservable on this latter date, as it skirts the open star cluster M35).

Venus

Venus continues to strut its stuff in our morning skies, carrying on from where it left off last month. It actually achieves its greatest angular separation from the Sun on the 3rd, although riding a little lower in the morning sky than it did last month due to the fact that the ecliptic rises less steeply from the June morning horizon.

On the 1st of the month, the brilliant orb crests the ENE horizon at 3:38 am; it is already 24° high in the NE when twilight commences at 5:53 am and 38° NNE at sunrise, 7:26 am. Venus’ disk has reduced in apparent size from the dizzy heights it reached last month, but still spans an impressive 25" at an appealing phase of 48%, blazing forth at magnitude -4.3 (some resources give its magnitude at this time as -4.5; figures quoted here are taken from Starry Night software).

On the 3rd and 4th, Venus passes less than 2° from Uranus (as a rough guide, one finger held at arm’s length spans a little over 1°, a closed fist 10°, an open hand, tip of little finger to thumb tip, 20°); see the notes on the latter for details. Venus’ orbital path takes it to its maximum distance from the Sun on the 12th, but this has no visually detectable effect on its brightness, which is very slowly decreasing as it moves away from Earth throughout the month.

On the morning of the 25th, corresponding to our viewing night of the 24th, Venus rises at 4:01 am; its altitude at the commencement of twilight (6:02 am) and sunrise (7:36 am) is respectively 20° and 32°, at the same compass points as for the start of the month.

At month’s end the above data read 4:08 am, 6:02 am, 7:37 am, 19° and 31°; compass points remain as above. Venus will remain above the sunrise horizon throughout the year (just), but loses a good deal of altitude throughout July and August, entering twilight on Sept 2nd. While this lessens the spectacle, it still shines as only it can at magnitude -3.95 as it enters the twilight zone, and so continues to dominate morning views for months to come. Venus goes on tour this month, transitioning from Pisces into Cetus less than ten minutes after the calendar clicks over to the 10th, then into Aries in the early hours of the 11th and to Taurus on the 28th.

Earth

We in the southern hemisphere reach the winter solstice on the 21st (summer solstice north of the equator), when days are shortest and nights longest (vice versa in the north). Note that the times of latest sunrise and earliest sunset do not exactly coincide with the solstice or each other. They vary by latitude, and for Melbourne, Victoria, to which the various data in this column apply, latest sunrise occurs June 29 and earliest sunset June 13.

Mars

The combination of the fact that Mars is in conjunction with the Sun next month and its very slow progression towards same (by far the slowest of all the planets, due to it being our closest outer neighbour, whereby we outpace it on our inner orbital track only slowly) mandates that it spends this month close to the sunset horizon, particularly late in the month when our viewing night is scheduled.

The table below shows its particulars for the start of the month, viewing night and end of the month; as they indicate, the show’s all but over, and views of the Red Planet are best left until the second half of November when it emerges from twilight in the eastern sky.

Mars crosses the border from Taurus into Gemini on the 5th and remains there for the rest of the month.

Jupiter

Mighty Jupiter rules the night sky throughout June; while it sets in the early hours of the morning, it is perfectly placed for early evening views.

As the month begins, the King of the Planets is already 33° clear of the sunset horizon, and 48° in the NE when twilight is fully extinguished at 6:43 pm. It then transits at 8:31 pm, riding a little over 56° clear of the northern horizon, before setting at 2:45 am. The planet’s disk spans 40.8" and easily outshines even Sirius (Alpha Canis Majoris), the night sky’s brightest star, standing out against the starry backdrop at magnitude -2.2.

Jupiter is stationary with respect to the background stars on the 10th as it reverts from retrograde to direct motion (around the time of opposition, which Jupiter reached in early April, the outer planets cease to move eastward against the stars and instead track westward, a phenomenon caused by our changing viewing perspective as we overtake them on our faster, inner orbital track).

Come our viewing night of the 24th, the giant planet is even better placed for views early in the evening. Its altitude at sunset (5:09 pm) has improved to 48° in the NE, and is again just over 56° at both the cessation of twilight, 6:43 pm, and when transiting in the north at 7:01 pm. The King subsequently sets at 1:16 am, appearing just a little smaller, 38.1", than at the beginning of the month, but still shining strongly at magnitude -2.1.

The earlier chart dealing with meteor showers shows Jupiter’s position in the sky; the following magnified view is configured for 7:01 pm on the 24th (time of transit), and shows the four Galilean moons – Io, Europa, Ganymede and Callisto. The moons shine at magnitudes 5.6, 5.85, 5.2 and 6.2 respectively, and as the stars near them are seven or eight magnitudes fainter at best, they cannot be mistaken for the moons (or even seen through other than very large telescopes for the most part) and so have not been plotted.

There is a further reason for the 7:01 pm timeline other than the fact that Jupiter is transiting – it also depicts the upcoming occultation of Io, the innermost of the Galilean moons, by its parent (as to the other three, Europa and Callisto are moving away from Jupiter, while Ganymede is moving towards it). Watching through your telescope, you’ll see Io disappear behind Jupiter between 7:24 pm and 7:28 pm. Although the moon actually re-emerges from behind the planet over the interval 9:37 pm to 9:41 pm, you won’t see it do so, as it emerges into Jupiter’s shadow (i.e. it emerges from occultation into eclipse). It begins to clears the shadow and thus become visible at 10:52 pm, being fully clear by 10:56 pm, 20" from the planet’s eastern limb (about half the span of Jupiter itself).

There is yet another fortunate happenstance with regard to the timing – the Great Red Spot first starts to creep onto the upper eastern edge of the disk a little before 6 pm. It should be clearly visible in its entirety near the edge as Io’s transit begins, and will move across Jupiter’s face until beginning to disappear off the western edge around 10 pm.

Here’s the view as Io begins to slip behind Jupiter; as a matter of interest, two of its smaller and dimmer moons are shown to the left of the planet, Amalthea, magnitude 14.7 and Thebe mag 16.3; large ‘scopes (or time lapse imaging) will be required to pick them up, especially the latter. Notice also the fuzzy appearance of Jupiter’s disk around the eastern edge – although you won’t detect this in your ‘scope, it’s the result of the software depicting the 99.2% phase of the planet.

By the end of June, Jupiter is at an altitude of 51° when the Sun sets, and transits at the very convenient time of 6:39 pm, just seven minutes before the sky fully darkens, subsequently setting at 12:54 am; the disk still spans a generous 37.5" and shines at magnitude -2.05.

Jupiter, which will remain in the constellation of Virgo until November, will also be a de-facto player in this month’s feature – more about that later.

Saturn

Beautiful Saturn is at opposition this month, on the 15th, and the ring system is approaching its greatest inclination in almost fifteen years (peaking at 26.98° in October), so prime viewing time is upon us over the next few months.

As June gets underway, Saturn rises less than an hour after sunset – 6:04 pm vs 5:09 pm – and is at an altitude of 6½° when twilight fades at 6:43 pm. Its disk spans 18.4" (throughout the month), the rings 41.6" at an inclination of 26.55°; rings and disk together shine at magnitude 0.07.

If you’re a regular viewer of Saturn, you may notice that the rings look a little brighter in relation to the disk this month than at other times; this is due to what is known as the opposition surge or Seeliger Effect and is caused by the shadows thrown by individual ring particles being directly behind the particle concerned, and thus not falling on, and dimming, other particles.

On our designated viewing night of the 24th, nine days past opposition, Saturn rises at 4:27 pm, is at an altitude of 7° ESE at sunset, 5:09 pm, and rides 25° high in the east at the cessation of evening twilight, 6:43 pm. The span of the rings has improved marginally, to 41.7", and they have continued to open, to 26.65°; visual magnitude registers 0.04, having peaked at 0.0 on the 15th.

Consult the overview shown earlier in the section dealing with meteors to see where Saturn sits in relation to the constellation figures of Scorpius (one of the most easily recognisable patterns in the sky) and Sagittarius, then refer to the following magnified view, which is configured for 8:30 pm on the 24th, with Saturn at an altitude of 46° in the ENE.

Six of Saturn’s seven brightest moons are labelled here; top to bottom on the chart, they are: Dione, mag 10.6; Tethys, mag 10.4; Mimas, mag 13.1; Rhea, mag 9.9; Enceladus, mag 11.9 and Titan, mag 8.5 (also shown but not labelled is Janus, mag 14.8, just outside the right hand edge of the rings). As most of the stars closer to Saturn than Titan are 16th magnitude or fainter, with only a smattering at 15th magnitude and none brighter, they cannot be confused with the moons and are not depicted.

The next chart zooms out to pick up the seventh bright moon, far flung Iapetus. This enigmatic moon has one hemisphere much brighter than the other; as a consequence, its brightness from our perspective varies considerably more over its 79 day orbit of Saturn than over Saturn’s roughly 12½ month opposition to opposition cycle. Accordingly, whereas the magnitudes given above are taken from Starry Night software, that for Iapetus, magnitude 11.4, is my (confident) estimate, the software not taking the moon’s orbital cycle into consideration.

Identification of Iapetus is not as straightforward as for the others due to its distance from Saturn and the proximity to it of a star which, while considerably fainter than the moon, is nevertheless in the ‘ball park’. The star referred to is the rightmost of the two circled stars between Saturn and Iapetus, its designation is USNO J1732479-215914, and it shines at magnitude 12.4. The other circled star shines at magnitude 13.05 and is the only other star between Iapetus and Saturn which is in said ball park, the others being close to 15th magnitude or fainter, as are all stars in the immediate vicinity of the moon. The two stars towards the bottom of the chart are labelled with their magnitudes to assist in orientation, and also to illustrate the possibility of mistaking the dimmer of the two for Iapetus, star & moon having similar brightness and apparent distance from Saturn.

On June 30th, the Ringed Wonder is 30° high in the east when twilight fades at 6:46 pm. The rings span 41.6" at an inclination of 26.68°; disk and rings together shine at magnitude 0.07.

With a wide orbit, Saturn moves only slowly against the stars and so, having just last month back tracked across the border from Sagittarius into Ophiuchus under the influence of retrograde motion, it remains in that constellation throughout June – until November in fact, when it returns to Sagittarius after the resumption, in August, of direct motion.

Uranus

Uranus is now starting to attain a little altitude in our morning skies, especially towards the end of the month. At the start of June, it’s rising at 3:52 am, is 22° clear of the NE horizon when twilight starts to brighten the sky, and 35° high at sunup; its 3.4" disk shines at magnitude 5.88.

Venus is, as mentioned earlier, quite close to Uranus early in the month; the super bright guide post lies just under 1¾° away on the 3rd and just over 1¾° on the 4th; in both cases, Venus is to Uranus’ upper right, a little lower on the 4th than on the 3rd. Here’s the view on the 3rd at 5:54 am, just as twilight begins; Uranus is brighter (still mag 5.88) than any star in the immediate area bar that of magnitude 4.25; stars dimmer than magnitude 9.5 have been omitted to approximate the view through a finder ‘scope. White crosses indicate the positions of both planets on the 4th.

On the morning of the 25th (our viewing night being the 24th), Uranus has become an inviting target. Rise time is 2:22 am and the planet sits well clear of the NNE horizon, 36°, as twilight begins at 6:02 am (42°N at sunup, 7:36 pm); span and brightness are marginally improved to 3.5" and magnitude 5.85. Here’s an overview, configured for 6:02 am on the 25th, for locating Uranus (and Neptune for later reference):

By relating the above chart to what you see in the sky, identify the Great Square of Pegasus, in particular the star at its top right corner, Algenib (Gamma [γ] Pegasi), magnitude 2.8, and also the fainter, but still comfortably naked eye, Eta [η] Piscium, magnitude 3.6. Noting that Uranus is at the apex of an isosceles triangle with base Algenib to Venus, proceed to the magnification below:

Having identified Eta Psc (labelled with its visual magnitude of 3.59), the above chart should allow you to identify Uranus through your finder ‘scope. Just note that Eta Psc, Pi [π] Psc (the star of mag 5.53), Uranus and Omicron [ο] Psc (mag 4.25) form an almost straight line, and that all other stars in the area are dimmer, save for HIP8588 which, at magnitude 5.90 as shown, is essentially the same brightness as your planetary target. As a guide to star hopping through your finder ‘scope, note that ‘3.59’ and ‘5.53’ will fit comfortably within the field of view provided by your finder, as will the pair of ‘5.53’ and ‘4.25’, and that ‘5.53’ is almost exactly midway between the other two. Uranus’ relatively steady shine compared to the often twinkling stars (why is this – if you don’t know, look it up or drop me a line at the contact address at the end of these notes) and its subtle blue-green hue will also aid in identification.

When you think you’ve identified the planet, switch to the main eyepiece at a magnification of 150x or more (250x is better) to confirm capture by resolving its tiny disk, the colouration of which will appear considerably richer than through the finder.

On June 30th, Uranus rises at 2:03 am and is 37° above the horizon at the beginning of morning twilight, 6:02 am; the span of the disk, the brightness of which is up incrementally to mag 5.84, is unchanged from the 25th. Uranus will meander slowly through the constellation of Pisces until 2018/19.

Neptune

The outermost planet (aside from Pluto, which still gets a mention in this column) can officially be said to attain evening planet status this month, rising before midnight from the 6th onwards.

On the 1st, the ice giant – a descriptor applied to both Neptune and Uranus – rises at 12:21 am and is at an altitude of 57° as morning twilight commences at 5:53 am; its disk spans 2.3" (all month) and shines at magnitude 7.89.

When our designated viewing night of the 24th arrives, Neptune rises at 10:47 pm, then transits at 5:11 am, at an altitude of 59°, more than ¾ hour before morning twilight starts to flood the sky at 6:02 am; visual magnitude is up, albeit imperceptibly, to magnitude 7.86. To locate the planet, first refer to the wide field view in the above notes on Uranus and identify, in the sky, the two asterisms The Circlet in Pisces and, to its left, the ‘Y’ of Aquarius, each composed principally of 3rd and 4th magnitude stars, and so visible to the naked eye, albeit faintly so with regard to some components. Having done so, refer then to the following chart, which zeros in on the area encompassing the ‘Y’ and Neptune, depicting the view at 2:00 am on the 25th, by which time the planet has attained a respectable altitude of 37°.

Use this chart to identify Lambda [λ] Aquarii, mag 3.7, and Phi [φ] Aqr, mag 4.2. Such identification should not be difficult using just the naked eye as Kappa [κ] Aqr, mag 5.0, is the only star brighter than mag 5.7 between the ‘Y’ and the pair of Lambda & Phi, and so the only one you’ll see, unless your sky is pitch black and your eyesight keen. Note that Sadachbia (Gamma Aqr, mag 3.8), Kappa Aqr and Lambda Aqr form a nearly straight line, with Kappa just under 5° (roughly half the span of a fist held at arm’s length) from each of the other two. With Lambda & Phi Aqr firmly in your sights, proceed now to the final chart below, which is delimited by those stars (which are circled).

As this chart is intended to be used in conjunction with your finder ‘scope, only stars brighter than magnitude 9.5 are plotted, so what you see through your finder will be close to what you see on the chart. All stars which lie between Lambda & Phi, and which are brighter than Neptune, are labelled with their magnitudes. Note that Neptune lies near the grouping of relatively bright stars roughly half way between Lambda & Phi (a little closer to the former), and, at magnitude 7.86, is only marginally fainter than the star of magnitude 7.68 (HIP113709).

As was the case with Uranus, identification of the planet may be aided by its steady glow and subtle colouration, blue-grey in this case. Again, confirm capture by switching to the main eyepiece to resolve Neptune’s miniscule disk; the highest practical magnification (I suggest 250x or more) and careful examination are the tools of the trade for this exercise. Because Neptune is stationary relative to the stars mid-month (on the 17th), it will barely move, at the resolution of this chart, from its plotted position throughout the month.

As June comes to an end, Neptune breaches the eastern horizon at 10:23 pm, then transits at 4:47 am. Visual magnitude is unchanged from the 25th; the planet will remain within Aquarius until 2022/23.

Pluto

Pluto reaches opposition in the second week of July; correspondingly, a chart of intermediate resolution will this month compliment the usual general directions, followed by a detailed finder chart in July and the months to follow. On June 1st, the tiny frozen orb rises at 7:48 pm and transits the following morning at 3:00 am; it glows gently at magnitude 14.21 and spans 0.098" (throughout the month), far too small to be resolved by amateur instruments.

On the night of the 24th, matters have improved somewhat – rise time is 6:15 pm, just under ½ hour before evening twilight fades, and the planet transits at 1:28 am (on the 25th); it shines a touch brighter, at magnitude 14.17. The wide field chart accompanying the meteor notes shows its general location near the three naked eye stars not far from the handle of the Teapot asterism in Sagittarius. Here’s a magnified view, configured for 10:00 pm on the 24th, with Pluto at an altitude of 42°; only stars brighter than magnitude 5.5 are plotted to approximate a naked eye view. Xi22] Sag, Omicron Sag and Albaldah (Pi Sag), the three stars referred to above, shine at magnitude 3.5, 3.75 and 2.9 respectively. Saturn is also plotted as a reference.

The next chart shows stars down to around magnitude 12.8, still much brighter than Pluto; it labels Albaldah, mag 2.87, to enable you to relate it to the previous chart. Also labelled is the next brightest star shown, HIP95077, mag 5.56, which you may be able to spot with the naked eye, and the brightest star within ½° of Pluto, TYC6308-1224-1, mag 7.37.

This chart is obviously unable to pinpoint Pluto itself; next month we’ll introduce a further magnification which will enable identification with a suitable instrument.

On the final day of the month, Pluto rises at 5:51 pm, almost an hour before evening twilight expires; it subsequently transits at 1:04 am, shining at magnitude 14.16. Pluto will continue to inhabit Sagittarius until 2023/24.

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Our Monthly Feature

The quite beautiful object that is the subject of our feature this month figured in the feature article of April last year, when we looked at the constellation of Hydra as a whole. The object in question is NGC 3242, the planetary nebula known as The Ghost of Jupiter, aka Jupiter’s Ghost or The Eye. I hadn’t viewed the nebula before last April and time & circumstances did not permit doing so before the publication deadline, but having done so since, was gobsmacked at its appearance. While the outlying detail which gave rise to the ‘Eye’ label was not visible, what did present at high magnification – which the Ghost handles very well – was a large, aesthetically pleasing disk with a rich blue colouration. We’re all used to seeing magnificent colour images, usually enhanced, taken by professional grade ‘scopes using time exposures, but views through the eyepiece of amateur ‘scopes are, in the vast majority of cases, basically monochrome – this beauty is a standout exception to that unfortunate rule.

The result of an expanding shell of gas puffed off by a Sun-like star at the end of its life, NGC 3242, which lies around 1400 light years away, was first observed by William Herschel on 7/2/1785, and received its New General Catalogue designation in 1888. One online source credits Robert Burnham Jr (1931-1993), an American astronomer and author, with imparting the Ghost of Jupiter tag – its captivating blue colouration is far more reminiscent, however, of Uranus, albeit far larger, ½ - ⅔ the size of Jupiter.

As NGC 3242 is located only a little over the span of an open hand at arm’s length from the ecliptic, the planetary and its namesake planet are reasonably close in the sky every twelve years or so (Jupiter orbits the Sun every 11.86 years), lending another dimension to the relationship – the pair were at their closest around this time last year, and as such are still in relative proximity, about 39° part. Spanning 25", and shining at magnitude 8.6, the nebula is too faint to be seen with the naked eye and quite faint and star like even through a finder ‘scope; it is nevertheless not difficult to find with the right approach. First consult the following overview, which is configured for when twilight fades at 6:43 pm on the 24th – I recommend this early view to catch the planetary high in the sky (56°), where the best views are to be had.

Starting from prominent Jupiter, first look SSW (above and slightly left) for the easily recognisable quadrilateral of Corvus. Next, by relating the chart to what you see in the sky, identify Hydra as it snakes its way across the sky, in particular Mu [μ] Hydrae, magnitude 3.8, the closest star of the constellation figure to the planetary. Once you’ve found Mu Hya, refer to the magnification below, which shows stars down to about magnitude 9.5, close to the resolution of a finder ‘scope.


All star charts courtesy of StarryNight®ProTM Version 7.5.6.1208/Simulation Curriculum Corp.

There are two ways to proceed from this point: use the finder ‘scope to identify the faint star like nebula, or at least its position, before switching to the main eyepiece, or slowly sweep the sky a couple of degree (about 1½ fingers at arm’s length) from Mu using the main eyepiece at medium power – say 100x or a little less – to detect and resolve the span of the nebula directly. The latter method (which I recommend) is self-descriptive; if you employ the former, proceed as follows:

First centre Mu in the field of view of your finder ‘scope. Now look for the five relatively bright stars (two pair and a single, the single may be outside the field of view) in a near-horizontal straight line above Mu as shown on the chart (remember your finder may invert the view, in which case the line of stars will be below Mu). The planetary is just to the upper left (on the chart) of the central pair of the five, a little over ½° away, about ⅓ the span of a finger at arm’s length. If you can identify the nebula as a faint ‘star’ by reference to this pair of stars, centre it (don’t mistake it for the magnitude 8.6 star, TYC6065-860-1, the same brightness as the nebula, faintly visible on the chart halfway from the pair to the target), else centre the appropriate spot, then switch to the main eyepiece at around 100x. The small blue disk should be in the field of view, if not, slowly sweep around – it can’t be far away.

Whichever method you employ, once you’ve located the Ghost, bump up the power to the maximum practical magnification to fully appreciate what really is a truly captivating sight, and hop over to Jupiter to compare the span of nebula and planet.

That concludes this edition of The Australian Night Sky.

As always, any questions, comments or suggestions are welcome and may be directed to: waynerobertsau@yahoo.com.au

Until next month:

CLEAR SKIES and HAPPY HUNTING