Trot out your ‘scope and take advantage of the warm Summer nights with:
[Click here to show or hide the explanatory notes]
1st Close conjunction between Mars and Neptune (see planetary notes below).
3rd Neptune and Mars both occulted by Moon (not from Australia).
4th Quadrantid meteor shower peaks.
5th Earth at perihelion (closest to Sun, 147.1 million km / 0.9833 au).
6th First Quarter Moon.
7th Pluto in conjunction with Sun.
8th Mercury stationary.
10th Aldebaran (Alpha [α] Tauri, magnitude 0.8), occulted by Moon (not from Australia);
Moon at perigee (closest to Earth, 363,238 km).
12th Full Moon;
Venus at greatest elongation east (farthest from the Sun, 47° @ midnight 12th/13th).
15th Regulus (Alpha Leonis, magnitude 1.3) occulted by Moon (not from Australia).
18th Asteroid 4 Vesta at opposition.
19th Mercury at greatest elongation west, 24°.
20th Last Quarter Moon.
22nd Moon at apogee (farthest from Earth, 404,194 km).
28th New Moon.
30th Neptune occulted by the 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.
As indicated above, the Moon has a series of meetings with both planets and stars this month; while all result in occultations from various vantage points around the globe, we in Australia unfortunately see only close passes at best.
First to be visited in our skies by Earth’s satellite, on the 3rd, are Neptune and Mars, in daylight at 1:38 pm and 5:05 pm respectively. In each case, the upper limb of the Moon passes 26' – less than ½° – from the planet; NE, or below left, in the case of Neptune, with the planet at an altitude of 33° in the east, and north (below) for Mars, which sits 60° high (in the north). The lunar disk displays a 23% waxing crescent phase as it passes by Neptune, and has fattened marginally to 24% for the Mars encounter.
On the 10th, Aldebaran is 14° above the NW horizon when it sits 40' SE or upper left of the 89% illuminated waxing gibbous Moon’s limb. This is the 27th in a series of 48 occasions, running from January 2015 until September 2018, on which Aldebaran is occulted by the Moon from somewhere on Earth.
Regulus undergoes its 2nd of 19 occultations – the first of which occurred last month, with the last slated for April of 2018 – on the 15th. While this event results in the closest passage of all, with the Moon’s limb passing just 10' from the star, it is further out of our reach than those previously mentioned, with the Moon (displaying a waxing gibbous phase, 91% illuminated) and planet more than 60° below our southern horizon.
Finally, Neptune is again, for the second time this month, occulted by the Moon from locations outside Australia (Africa, South Asia and South Arabia). From our perspective, closest approach of marginally under ¾° occurs below our WSW horizon at 11:11 pm, the pair having set about 1¼ hour earlier.
Only one meteor shower reaches its peak this month, the Quadrantids. This shower gets its name from the obsolete constellation of Quadrans Muralis; present day sky charts apportion the area of sky containing the shower’s radiant – the point from which the meteors appear to emanate – to the constellation Bootes; the shower is consequently sometimes referred to as the Bootids. Although the Quadrantids are intrinsically a major shower, with a ZHR of 120, the radiant lies quite deep in the northern hemisphere and only ever barely breaches our northern horizon, reaching a maximum altitude of less than 3½°. Obviously this will heavily impact the number of meteors seen, and the situation is made considerably worse still by the twin facts that this shower has a narrow, short lived peak – a few hours at best – and that peak, expected to be at 1:00 am on the morning of the 4th, occurs when the radiant lies a massive 54° below our NE horizon. Even when morning twilight begins to paint the sky, at 4:11 am, the radiant is still 24° on the wrong side of the horizon.
These negative factors are a real pity because the Moon remains out of our skies after setting at 11:53 pm on the 3rd. Poor though prospects may be, intrepid meteor observers may catch a few long lived meteors streaming up over the horizon; consequently the below chart is provided (with the horizon shown as a white line), configured for 1:00 am on the 4th, with the position of the radiant when twilight begins marked with a white cross.
The asteroid (or ‘minor planet’) 4 Vesta is at opposition, and hence peak brightness, on the 18th. As it will only suffer a very small drop in brightness – from magnitude 6.1 to 6.3 – between now and next month, we’ll deal with it in detail then, as a feature article, when it will be available for viewing at a friendlier hour. In the interim, the following chart shows where it sits at 12:45 am on January 28th, this month’s suggested viewing night (being a Saturday and the date of New Moon).
The prominent ‘twin’ stars of Gemini, Castor (Alpha Geminorum, mag 1.6) and Pollux (Beta [β] Geminorum mag 1.15), point almost directly at the asteroid, and in conjunction with the unlabelled star shown just to its left on the chart, Kappa [κ] Gem, comfortably naked eye, although not bright, at magnitude 3.6, should aid in identification. Kappa Gem is only 1¾° (about 1½ times the width of a finger held at arm’s length) from the space rock. The asteroid is considerably brighter than all stars in its immediate vicinity; the brightest of these – and the only ones anywhere near as bright as your target – are two of mag 7.1 flanking one of mag 7.8 in a gently curving arc between Vesta and Kappa Gem, closer to the former (if you include Vesta in the arc, it forms a semi-circle). The inset illustrates this, with Vesta’s position on the 27th and 29th (at the same time) also indicated.
Having been at inferior conjunction, swinging in between Earth and the Sun on its inner, faster, orbital track on the 29th of last month, the innermost planet spends January in the eastern morning sky, struggling to break free of twilight, but never quite managing to do so. On the 1st, it rises at 5:42 am, and is a mere 3° clear of the horizon at sunrise just under 20 minutes later. Only 4% illuminated, its 10" disk shines feebly at magnitude 3.1; consequently it is totally consumed by twilight and unobservable.
As the days pass, Mercury pulls away from the Sun in our sky, quite rapidly at first, even outpacing the westward moving stars until the 8th. After this date the starry backdrop outpaces the planet as both move westwards daily, but Mercury continues to rise earlier and increase its angular distance from the Sun in our morning skies until the 19th when it reaches a maximum separation from our local star – known as greatest elongation west – of 24°. On this morning, it rises at 4:31 am, and flirts with breaking free of twilight, being at an altitude of just over 19¼° when the Sun breaches the eastern horizon at 6:19 am.
While Mercury’s angular separation from Sol decreases daily after this point, its vertical altitude above the horizon at sunrise, and the time differential between its rise time and sunrise, continue to increase slightly until the 25th, reaching a touch under 20° and in excess of 1 hour 51 minutes respectively. This counter-intuitive phenomenon occurs because the ecliptic – the path followed across the sky by the Sun and (very nearly) the planets, steepens in the morning hours throughout the month, resulting in the planet moving away from the horizon more quickly.
By the 28th, our suggested viewing date (and also the date of New Moon), Mercury is in retreat, descending towards the morning horizon a little faster with each passing day; it rises at 4:39 am, and its sunrise (6:29 am) altitude has declined slightly to a little over 19½°. The planet’s disk, reduced in apparent size to 5.9" as it continues to pull away from Earth, is then 77% illuminated and shines at magnitude -0.17. Here’s the view at 5:29 am, one hour before sunrise, with Mercury just under 8½° above the horizon:
Come the end of the month, Mercury rises at 4:45 am, and is less than 19¼° clear of the horizon when the Sun rises at 6:32 am; its disk, shining more brightly by the barest of margins, at magnitude -0.18, spans 5.7" and is 80% illuminated.
As indicated last month, Mercury remains within Sagittarius all month.
Venus continues to blaze brilliantly in the western sky throughout January evenings, reaching greatest elongation east, 47° (from the Sun) on the 12th. Although its altitude in our skies falls throughout January (even in the lead up to the 12th, courtesy of the steadily reducing angle the ecliptic makes with the evening horizon), it remains clear of the twilight zone all month.
In addition to Venus’ unrivalled naked eye presence, it also presents a fascinating telescopic sight this month and a good deal of next, courtesy of an increasing span and decreasing phase, culminating in a huge crescent in mid-February.
As January begins, the scintillating orb remains above the western horizon until 11:24 pm, having been at an altitude of 30° at sunset, 8:45 pm; its disk spans an already impressive 22", is 56% lit, and blazes forth at magnitude -4.3. At greatest elongation east on the 12th, its setting time has come forward a little as indicated above, to 11:06 pm, and sunset (still 8:45 pm to the nearest minute) altitude is down to a still generous 27°; the span of the disk is out to 24", its phase down to 51%, and it shines still brighter at magnitude -4.4.
On our suggested viewing night of the 28th, setting time is in to 10:33 pm, but the planet is still at an altitude of 22° when the Sun sets at 8:36 pm. The telescopic spectacle is becoming ever more impressive, with a huge 29" disk in a noticeably crescent phase at 42% lit; as is the naked eye view with Venus dazzling the eye at magnitude -4.5. The following chart shows the scene at 9:06 pm, ½ hour after sunset, with three other planets labelled for later reference. Whereas views of virtually all the other planets – Jupiter possibly excepted – so soon after sunset suffer due to twilight illuminating the sky, Venus watchers actually benefit as its overpowering glare is reduced.
Even as the month ends, Venus is 21° high as the Sun sets and still lingers in the western sky until 10:26 pm. The telescopic view has become yet more appealing, the disk spanning 31" with the crescent phase reduced to 40%; brightness has by then reached an astounding mag -4.6.
Venus transitions from Aquarius into Pisces on the 23rd, remaining in that constellation for the balance of the month.
While Mars still stands in our evening western sky, it drops just a little lower with each passing day. The Red Planet’s speedy eastward movement relative to the stars – far faster than any other outer planet (those that orbit farther from the Sun than does Earth), and a consequence of the fact that it is our immediate neighbour, whereby we only slowly pull away from it on our inner orbital track – delays its trek towards the western horizon, but its days are numbered.
Even at the start of the month, the planet is setting at 11:52 pm, having been at a less than generous altitude of 14° when evening twilight fully subsided at 10:39 pm. The martian disk is noticeably less than fully lit (the only outer planet to appear as such), at a phase of 90%, spans a very small 6" – too small to show surface markings through most amateur instruments – and shines at magnitude 0.9. This first day of the month is noticeable for Mars’ very close conjunction with Neptune – see the notes on the latter for more detail.
Come our viewing night of the 28th, Mars sets at 10:54 pm, and is a miserly 6° clear of the western horizon when the sky fully darkens at 10:20 pm; the span of the disk has reduced to 5", 92% illuminated, and it shines at magnitude 1.1. Mars sits very near Venus, as shown in the earlier chart, only 5½° separating the pair, and will be a push over to identify due to the lack of naked eye stars in its vicinity – no further chart is required in this regard.
Three days later on the 31st, Mars is just 5½° high at the cessation of twilight, 10:16 pm, and sets at 10:47 pm; span, phase and brightness are essentially unchanged.
By the end of next month, the planet will set a mere 13 minutes after twilight ceases to paint the sky, so don’t delay if you wish to view it; Mars leaves Aquarius for Pisces on the 19th.
The King of the Planets rules the sky in the pre-dawn hours, and even qualifies for the title of evening object late in the month, rising at midnight on the 26th and progressively earlier thereafter.
On New Year’s Day, Jupiter rises at 1:33 am and is 50° high in the NE when the Sun also rises, at 6:02 am; the giant planet’s disk spans 36" and shines brighter than any star at magnitude -1.9.
The situation is further improved on our viewing night of the 28th, with the King marching over the eastern horizon at 11:49 pm, and even transiting just over ¼ hour before sunrise (6:14 am as against 6:30 am, on the morning of the 29th). The span of Jupiter’s disk has increased to 39", and it shines even more brightly, at magnitude -2.1. Although its brilliance makes identifying it an easy task, here’s an overview showing where it sits at 3:25 am on the morning of the 29th, one hour and twenty one minutes before the commencement of morning twilight. Some prominent constellations and stars are labelled to aid in orientation, as is Saturn for later reference.
Why 3:25 am, you may ask in relation to the above chart; this time was chosen to facilitate observing Io, the innermost of Jupiter’s four Galilean moons, emerging from behind the eastern limb of the planet between 3:31 am and 3:35 am. This is a very interesting exercise in its own right, and has the added benefit of emphasising the fact that the moons are not simply points of light under telescopic magnification. While they may appear point like at first glance, the act of watching the moons emerge from behind their parent quite graphically shows that this is not the case. If you’ve not done this before, try it – the effect is quite pleasing. Here’s where moons sit at 3:35 am, and a close up of Io’s re-emergence.
On January 31st, Jupiter is rising a little earlier, 11:37 pm; span and brightness remain as stated above; the planet resides within Virgo until November.
Having been in conjunction with the Sun on Dec 10th, Saturn sits in our morning skies this month, very close to the horizon at sunrise and rising higher as the month progresses.
As 2017 begins, the Ringed Planet rises at 4:45 am, 38 minutes after the commencement of morning twilight; its disk spans 15" and the rings 34", inclined at 26.8°; disk & rings together shine at magnitude 0.49.
Come the 28th, the night of our viewing, it’s rising considerably earlier, at 3:07 am (on the 29th), and is at an altitude of 18° when twilight begins at 4:46 am; the disk still spans 15", while the rings are out to 35" at a slightly reduced inclination of 26.7°; the system shines at magnitude 0.54. By the end of the month, these figures read 2:59 am, 20°, 4:50 am, 16", 35", 26.7° and 0.54.
Two issues need addressing in relation to these data. Firstly, while the inclination of Saturn’s ring system from our perspective is still in a long term increasing trend, due to max out at 26.98° in October, it is currently in the grip of a short term closing trend (from the start of the year until mid-April, when it’s down to 26.42°) due to our changing vantage point as we move along our orbital track.
Secondly, regular readers will recall from last November’s viewing notes, that Saturn was seen to counter-intuitively increase slightly in brightness as it approached conjunction. Planets are expected to be brightest at opposition, when close to Earth, and dimmest at conjunction, when farthest from us. Saturn did adhere to this natural trend other than for exhibiting a slight increase in brightness in the month and a half or so leading up to conjunction. I remain uncertain as to the cause of this strange phenomenon (a number of possible reasons were canvassed in November), and it plays out again in reverse in the period after conjunction, when the brightness unexpectedly decreases from mag 0.43 at conjunction to 0.54 one week into February – hence the figures given above indicating that brightness decreases from mag 0.49 to 0.54 throughout January. I’ll make a concerted effort in the lead up to compiling next month’s notes to come to grips with this – stay tuned.
Saturn’s location in the morning sky is illustrated in two of the preceding charts, in the Mercury and Jupiter notes; as it’s still quite low in the sky, we’ll leave it at that for this month, without exploring the positions of its major moons – there’s plenty of exciting action to come later in the year as it rises away from the horizon and also opens the ring system to its maximum extent.
Saturn is in the constellation of Ophiuchus throughout January and for most of this year.
Uranus has hung in our evening skies for some months now and this apparition is past its prime. Even at the beginning of the month, it transits more than 50 minutes before sunset and is only 30° high – still respectable but at the lower limit of what this column holds to be an acceptable altitude for good views – when the sky fully darkens at 10:39 pm, before setting at 1:31 am; its very small 3.6" disk shines at magnitude 5.79.
The situation has further deteriorated on the night of the 28th, with the planet hanging just 16° above the WNW horizon when twilight fully fades at 10:20 pm; span and brightness are down marginally to 3.5" and magnitude 5.84. The chart in the notes on Venus shows Uranus’ position at 9:06 pm, ½ hour after sunset. Use it to fix the planet’s approximate position in the sky by reference to Venus, Mars, Algenib (Gamma [γ] Pegasi, mag 2.8) at the top of the Great Square of Pegasus, and the pair of Hamal (Alpha Arietis, mag 2.0) & Sheraton (Beta Arietis, mag 2.6). Note, on the same chart, the two fainter stars to Uranus’ lower left, Epsilon [ε] Psc, mag 4.25 (the closer of the two) and Delta [δ] Psc, mag 4.43 – while faint, they are comfortable naked eye captures under a dark sky. Even closer to Uranus, again to its lower left and forming very nearly a straight line with the two aforementioned stars, is Zeta [ζ] Piscium, barely naked eye at magnitude 5.18 (note that Zeta is a double star, appearing as one to the naked eye, the combined glow of the two registering magnitude 4.9). Having identified these three stars (or at least the brightest two), refer to the following chart, on which stars are labelled with their magnitudes:
This chart should facilitate identification of your target through a finder ‘scope, due to its proximity to Zeta Psc (labelled mag 5.18; actually mag 4.9), there being less than 1° (a little less than the span of a finger at arm’s length) between them – Epsilon Psc is only 3½° from Uranus and will also fit comfortably in the same field of view. The planet’s position on the 28th is indicated by the blue ‘star’ between its white markers for the start and end of the month, close to the latter; its label has been omitted for clarity of display. Note that Uranus moves very little relative to the stars this month; this is a consequence of the fact that it was stationary on the 30th of last month as it ended retrograde motion and resumed direct motion (see the explanatory notes at the beginning of this article). The chart also labels, as visual aids, ‘6.03’ (88 Psc) and ‘5.50’ (80 Psc); Uranus’ brightness is midway between that of these two stars; no other stars in the vicinity are as bright as the planet. Uranus’ subtle blue green hue and steady shine relative to the twinkling stars will help to make it stand out.
When you think you’ve nailed the planet, confirm your capture by switching to the main eyepiece at a magnification of 150x or more to resolve its disk – the colouration at this increased magnification is pleasingly vivid.
As the month concludes, Uranus is setting at 11:34 pm, span and brightness remain as above.
Uranus will remain within the constellation of Pisces until 2018/19.
This apparition of Neptune is all but done and dusted as it heads toward conjunction with the Sun on March 2nd. Early January is your best chance, as the outermost of the planets proper sets within twilight after the 22nd; even this early viewing is marginal, as the very first day of the month sees it setting at 11:51 pm, and riding only 14° above the western horizon as twilight ends at 10:39 pm; its tiny disk spans 2.2" (all month) and shines at magnitude 7.93.
This opening day of January is notable for an event which positively demands disregarding the planets less than optimal positioning, and viewing through your ‘scope or binoculars. The event referred to is an extremely close conjunction with Mars – it is only 9', less than 1/6th degree, to the WSW or lower left of the Red Planet as twilight is extinguished, the gap between the two having been just 1' five hours earlier.
Refer to the chart in the Venus notes to determine where Mars and Neptune sit in the sky. Note that this chart is configured primarily for the 28th, but Neptune will be at very nearly the same position on the 1st, and so Mars will also be at the far left of the chart rather than where shown. Having thus identified Mars, centre it in your finder ‘scope (or mounted/steadily held binoculars) and see if you can spot Neptune, very close to it. Look closely at the following chart to see the small dot representing Neptune within the large ‘star’ symbol for Mars, to the lower left of centre.
Switch then to the main eyepiece at medium to high magnification to easily resolve the pair – without going into the specifics of how the true field of view of a given telescope/eyepiece combination is calculated (perhaps a worthy subject for a future feature article), my twelve inch reflector, for instance, when fitted with one of my favourite eyepieces which provides a magnification of 250x, provides a field of view a little under ¼° across, thus spacing the planets (around 1/6th degree apart) nicely. This is the magnification I suggest to not only separate the planets but also to resolve Neptune’s tiny 2.2" disk at the same time.
By the time our viewing night of the 28th comes around, Neptune sets at 10:07 pm, a little over ten minutes before twilight fully fades, so the earlier viewing opportunity detailed above is far preferable; visual brightness has reduced marginally to magnitude 7.95. Setting time at month’s end is 9:56 pm; brightness is unchanged.
Neptune is in Aquarius, where it will remain until 2022/23.
The outermost planet (irrespective of the boffins’ call) is in conjunction with the Sun on the 7th; obviously it will be unavailable for viewing this month, and it will be some months, in fact, before this column gives detailed directions for locating it in the sky.
For the record, Pluto sets at 9:02 pm on the 1st, just over ¼ hour after sunset, and rises at 4:43 am on the 31st, more than ½ hour after morning twilight commences; its miniscule disk and visual magnitude are invariant throughout the month, at 0.093" and magnitude 14.3. Pluto will remain within Sagittarius until 2023/24.
This month’s feature article concerns four open star clusters, M35 in Gemini and M36, 37 & 38 in neighbouring Auriga. Open clusters are groups of stars which all formed around the same time (in astronomical terms) when a pre-existing and previously stable cold cloud of gas – primarily molecular hydrogen – and dust is gravitationally disrupted by, perhaps, the close passage of a passing star or a nearby supernova. The cloud begins to collapse in pockets and draw in more material from its surroundings, each destined to become a star if sufficient heat and pressure builds up in its core to initiate nuclear fusion.
All four of our targets are visible in binoculars or a finder ‘scope; M35 can even be seen as a misty patch with the naked eye. The ease with which a given target is found in the sky largely depends on which reference point is chosen from which to begin your search. Refer to the following chart, configured for the 28th at 10:20 pm, the cessation of evening twilight:
All star charts courtesy of StarryNight®ProTM Version 18.104.22.1689/Simulation Curriculum Corp.
In my experience, the easy way, and it is quite easy, to find the four open clusters is to first locate, with the naked eye, their prominent big brothers, the Pleiades and Hyades – as my software wouldn’t co-operate in labelling the latter, the prominent star Aldebaran, which is actually a foreground star and not a member of the cluster, is labelled in lieu. First, we’ll look at finding the relatively tight trio of M36-38, addressing the outlying M35 later.
Construct, in your mind’s eye, a line connecting the Hyades and Pleaides, then look to their NE (lower right) for the quite prominent naked eye stars Elnath (Beta Tauri), mag 1.6 and Hassaleh (Iota [ι] Aurigae), mag 2.7. Be careful you don’t find yourself looking at Zeta [ζ] Tauri, mag 3.0, and Elnath instead of Elnath and Hassaleh respectively A line between the two stars of concern runs almost parallel to that joining the two clusters; the distance between the two ‘lines’ is a little greater than that between the clusters. As the brightest stars between the two ‘lines’ are of 4th magnitude, and so quite faint, Elnath and Hassaleh are easy to identify.
You’re almost home – as the chart shows, M37, 36 & 38 form an almost straight line which is again oriented at a similar angle to the previous two lines and lies approximately half the distance from the star line as the star line is from the Hyades-Pleiades line. Theta [θ] Aurigae, magnitude 2.6, is also a handy guide, as shown by the chart. Employing your finder ‘scope (or binoculars), shift your gaze to the appropriate area of sky and pan around. You can’t help but come across at least one of the trio, and as 37 & 36 are visible in the same field of view, as are the pair of 36 & 38, coming across any one of the three will leave the other two at your mercy.
Once you’ve cornered your quarry, examine each in turn through the main eyepiece – 36 & 38 have a somewhat similar appearance to my eye, with 36 the most obvious of the two, while 37 shows a much richer population of stars, and is far more pleasing visually (this may be a subjective judgement, but I think you’ll agree).
Our final target, M35, is a little removed from the other three – 12° from the central M36, just a little over the span of a fist at arm’s length – but what it loses in neighbourly reference points it makes up for with increased visibility, to the point that it can be spotted with the naked eye. Additionally, despite its relative remoteness, we can again employ our tactic of constructing lines in the sky, and to further ease our burden, may use one we are acquainted with, that formed by the three Messier clusters.
Looking at the chart, you’ll see that a line from M38 to M36 points almost directly towards M35. Place 36 & 38 together in the field of view of your finder and note the angle of the connecting ‘line’. Then look, with the naked eye, in the direction so indicated towards M35; you’ll see two stars as shown, about as far apart as are 36 & 38. They are Tejat Posterior (Mu [μ] Geminorum, mag 2.8) and the slightly dimmer Propus or Tejat Prior (Eta [η] Gem, mag 3.3), unlabelled at Mu’s left in order to not clutter the field. To avoid confusion, note also the presence of Mebsuta (Epsilon Gem, mag 3.0) below and to the right, a star of similar colour and brightness. Once you’ve identified Mu and Eta Gem, just look, still with the naked eye, back in the direction and distance shown (about as far from Eta as Eta is from Mu) and you’ll spot the faint haze that is your target if your sky is reasonably dark. Alternatively, put Eta Gem at the appropriate side of the field of view of your finder and M35 will jump out at you. This final cluster is a good deal brighter than even M37, but not much larger. You can now turn the main eyepiece on the cluster and experiment with different magnifications to see which delivers the most pleasing view. As with M37, M35 will fill the field of view at high magnification (they’re both a good fit at 250x through my ‘scope).
That’s all we have for the opening edition of The Australian Night Sky for 2017.
As always, any questions, comments or suggestions are welcome and may be directed to: firstname.lastname@example.org
Until next month: