Harry sketches one of the favourite objects in the Australian summer sky – the Great Nebula in Orion

The Great Nebula in Orion, sketch by Harry Roberts

Like most amateurs perhaps, my first view of a nebula was M42 in Orion. In our summer skies the hero’s sword hangs upwards from his belt, and in 1962 a school friend showed me the “sword’s” central star with his 4” reflector. Back then Adelaide streetlights went off at midnight (truly) – and the sky was dark. The impact of seeing the “Great Nebula” for the first time is with me still, and recalls summer holidays of years ago.

For “sky sketchers” M42 is a big task – it‘s very large, with much complex detail, and has a huge brightness range. A while back a friend suggested an attempt on the nebula in pencil, with a series of images recording it in parts. Recently I made a start on the “Orion Project” from my backyard, to be augmented later from darker sites. Before starting I compiled a chart of the main background stars from astro-maps to save observing time The ten inch “dob” and the C8 were both used with the 14mm Radian eye piece – and surprisingly the static image in the C8 at 140x gave the best view. And what a view it was: the sky was surprisingly good with nearby trees enhancing the darkness.

Theta 1 Orionis, “The Trapezium”, was clearly seen as six stars, each brilliant and steady, with 10.5 mag. components E and F bright specks well clear of the four main stars. They all seemed to sit in a darker patch of the main nebula – perhaps a contrast effect. Theta 2 Orionis just to the SE with its two bright neighbours formed a line pointing almost due east. The background of the Great Nebula was peppered with small stars to <11 mag. I set to with pencil and blender to map as much of the nebula as possible over about 2½ hours, adding notes on brightness, detail sketches etc.

E. E. Barnard saw M42 as “resembling a great ghostly bat” in the Yerkes refractor, and Barnard’s “Bat” loomed over the bright nebula on the north side – being the only truly dark part of the whole field – all the rest was luminous to a greater or lesser extent, and it was soon clear that my chart covered only the brighter half of the nebula! The very nebulous star V372 marks the southern edge of my sketch – but is in fact the centre of the whole vast nebula.

Apart from the “Bat’s” wings and head (also called the “fishes mouth”), there was another smaller feature that looked truly black. This was a dark column that seemed to occult the inner bright region of the nebula about 1.5’ SW of the trapezium, with maybe a faint dust tail blowing away southwards; while I’ve viewed M42 many times I’d never seen the dusty feature! Perhaps this object is one of the cooler “trunk-like structures” sustained over light-years by magnetic fields – as some research suggests. This one in M42 is easier to see than most others in, say, the “Eagle Nebula” M16, or the Eta Carina nebula.

There was too much detail to record, and the outer parts of the nebula are only sketched in brief. Within its brightest parts the nebula contains incredible detail too that I will tackle in future sessions with the 4.8 Nagler (X400), and perhaps OIII and Hα filters as well – none were used for this first sketch.

Enjoy the summer nebula – the brightest in the sky.

Harry Roberts, Sun and Moon observer and member of the Sydney City Skywatchers

Harry reports on sunspot AR11036 – part of the recent upturn in the Sun’s activity

A large filament (a prominence seen edge-on) near sunspot group 11040 on the morning of Sunday 10 January 2010. Image taken in red hydrogen light by Monty Leventhal OAM

In H-alpha the sun can be amazingly active, but during solar minimum such activity has been rare. Material can be ejected from the sun in a variety of ways – and perhaps the strangest is the surge.

Surges occur near sunspots with strong umbral fields. Around such spots the chromospheric granularity is often very disturbed, and looks like long grass blown over by strong winds. Often in such regions dark (i.e. cooler) material can erupt from a point within or near the penumbra of a large stable spot, yet the material remains confined within a field structure. And what we see may at first look like more disturbed granularity – but the ejecta may then travel across a great distance (tens of Mm) often in a graceful curve. Sometimes a salvo of surges will erupt side by side as recently occurred in AR11036. Having reached a maximum distance from the “parent” spot – the surge often pauses for some time, before retracting backwards (backflow) along its original path – to disappear where it first emerged! While this sounds implausible, surges are relatively common around certain spots.

Sunspot AR11036, drawn by Harry Roberts

AR11036 emerged in the sun’s SW quadrant about Dec 20, with a few tiny preceding (p) spots and two or three larger following (f) spots, these in one penumbra (Fig). When I first saw it, alerted by Monty L, it was attended by several surges, including a trio (or salvo) over 40Mm in length. Other lesser surges or patches of disturbed granularity emerged from the group at points on the NE side. Sub flares were seen where the surges emerged – as is often the case. None of these were strong enough to cause a spike in the GOES X-ray background of GOES B1-class. A dark active region filament (arf) connected p and f spots, with bright plage throughout (Fig 1). No retraction phase was seen.

Shortly after (22:53UT) the same group appeared to host a filament ejection (Fig 2). This time very dark material emerged from points both south and north of the f spot group. This followed similar paths to the earlier surges, but was strongly tuneable in H-alpha – suggesting a Doppler shift in approach (i.e.bluewards). This suggests the ejection of one or more active region filaments (arf), as a strong shift is not usual in surges (that mostly stay near the solar surface – near vertical surge is a possibility). While this ejecta was visible on-band (central Hα) it grew very dark off-band while all other Hα detail vanished – a sign of high velocity in approach along line of sight. Strong flares usually follow filament ejections but only a sub flare was logged at 22:53 UT. A B4 at the site 40 minutes later may be associated, and the strongest C24 flare to date a GOES C7 erupted at the site six hours later together with a CME.

Clearly this small group was unusually active – having the strongest flare to date. Yet its white light appearance was that of a very minor group. It faded rapidly, and when near the limb the Mt Wilson Magnetograph recorded no detectable umbral field – Mt Wilson having been closed previously by weather conditions. We must guess at AR11036’s peak umbral fields – they were presumable strong, and recent northern group AR11035 had the strongest field yet for C24 of 2500 gauss. Are we witnessing a strengthening of C24 magnetic fields? Keep sun watching.

Harry Roberts, Sun and Moon observer and member of the Sydney City Skywatchers.

Harry sees a rare spot on the Sun and it is a large one – AR 11029

Sunspot AR 11029 on the surface of the Sun on the morning of Thursday 29 October 2009 (AEDT), image courtesy SOHO/MDI

The Astronomical Society of NSW (ASNSW) field day at Epping (Oct 24) was successful partly because there was something to see on the Sun. Members of the public could watch an emerging string of spots (AR11029) and when told they stretched across 50,000 km were suitably impressed. As well the clouds had more gaps as the day wore on. Half a dozen ASNSW members showed the Sun with a variety of methods, from image projection to narrow-band filters.

Sunspot AR 1109 (fig 1), drawing Harry Roberts

AR 11029 showed a tight cluster of small dark spots at the following (f) or east end, with a hint of two isolated spots well to the west (p) of the cluster. Timings showed the group covered about six degrees of longitude (Fig 1). In H-alpha some plage and a dark filament was recorded.

Sunspot AR 1109 (fig 2), drawing Harry Roberts

Clouds and heavy rain prevented further views until Oct 28 – when big changes in the group were obvious (compare Figs 1 and 2). During our cloudy days the professional websites showed rapid development in AR11029 and a big rise in GOES flaring, with several C class flares and dozens of lesser events. Fig 3 shows a B3 flare and associated ejection of dark material with detectable Doppler shift – a presumed filament ejection.

The writer keeps watch on the daily Mt Wilson umbral field magnetographs recording field strengths inside the sunspots themselves (hand-drawn). As you know current research suggests the sunspot fields have fallen to historic lows – and further decline is predicted. Figs 1 and 2 show the group in WL and H-alpha combined with the magnetograph closest in time on the right side of the Fig. (Note these are reversed project images).

AR11029 emerged (23rd Oct) with slightly stronger fields (2100G) in the (f) spot cluster and only 2000G in the isolated (p) spots. But things quickly changed. Even during the field day the isolated (p) spots became more distinct as they grew rapidly, although none seemed to have penumbra at the time. The magnetographs show that over the next few days stronger field emerged in the (p) spots while the (f) spots faded and disappeared – the tendency was for the group to shorten and concentrate magnetic flux at the western (p) end.
Fields there reached the strongest level yet recorded for a C24 spot of 2400G on the 27th. It’s easy to overstate the field strength argument. Several penumbral spot groups belonging to C24 have appeared since the cycle commenced in January 2008. The strongest fields recorded prior to the current group were 2300G in AR11024 (Jul 09) and 2300G in AR11008 (Nov 08). AR11019 had 2200G in May 09. So while 2400G is the strongest C24 field yet seen it represents only a small increase (100G) on the previous records – perhaps close to the equipment’s detection limits. Remember spots disappear around 1800G, and note the many at this level shown in Figs 1 and 2.

Sunspot AR 1109 (fig 3), drawing Harry Roberts

Through much of the 20th century sunspot fields were typically 3000G, yet the McMath-Pierce team find average fields currently at only 2200G. Do the 2400G detections suggest a turn-around in solar core fields? Clearly it’s too early to know. The present shortage of large prominences, disc filaments and penumbral sunspots confirms the weak core fields – and a turn-around may be a long way off. Still it was good to see an almost “normal” looking sunspot (Fig 2 and 3) with penumbra, visible filaments and some modest flaring.

Harry Roberts, Sun and Moon observer and member of the Sydney City Skywatchers

Harry finds a swan-like nebula – M17 the Omega Nebula

Omega Nebula drawn by Harry Roberts

Sketches of deep sky objects won’t win photographic competitions – but it is interesting to learn what that amazing detector, the human eye, can see through a telescope.

Discussing this recently I learnt that extended objects do not grow brighter as you approached them, and remain faint and colourless to human eyes. And the reason that digital sky images show rainbow hues is because cameras accumulate photons over time and so detect the true colour of the emitted light, red H-alpha, blue H-beta and green OIII etc. Having evolved on a planet with both dazzling sunlight and deep darkness our eyes lack the ability to see colour in faint extended sources.

When I came across M17 in the ten inch I realised I had forgotten how bright it was – a stunning swan shaped object that looks pretty much like its digital portraits – but with no sign of colour. Time is needed for a good sketch (as it is for photography) so the C8 (with diagonal and LPR filter) was used for this impression. Though the subject was fainter in the 8” the fixed image allowed more to be recorded (See sketch above).

The “swan’s” bright horizontal bar has much subtle detail with dark bands crossing it, and a milky light with brighter streamers formed the ghostly folded wings above the its “back”. The dark nebula below the swan’s neck stood out strongly as the darkest part of the whole field, with fainter nebula creating the “neck”. The head and bill of the celestial swan could be seen too, but unresolved stars may cause this. The “water” on which the swan floats was not dark either; faint wispy nebulae were visible there with averted vision.

Looking closely several faint stars were seen in the nebula –exaggerated in my sketch – as none of them were brighter than ~9 magnitude.

Messier saw it as “A train of light without stars, 5’ or 6’ in extent, in the shape of a spindle, a little like that in Andromeda’s belt (M31) but the light is very faint”. William Huggins was the first to study the light of M7 in a spectroscope (1866) and announced that the cloud was truly a mass of glowing gas, not a cluster of unresolved stars as Herschel senior thought – and it was the latter who coined the more common name Omega Nebula.

M17 is about 6,000 light years away and 12 light years from end to end. It is a very bright nebula, a good target for small ‘scopes, and visible as a bright patch in 8X40 binoculars; maybe it’s a naked eye object at a really dark site – a truly stunning winter [and spring] object!

Harry Roberts, sky sketcher and member of the Sydney City Skywatchers

Harry finds two women of science commemorated on the Moon

Finding diagram for craters Blagg and Bruce on the Moon, drawn by Harry Roberts

History ‘dogs’ us through time, always there to remind us that, while figure ‘A’ was showered with honours, ‘B’ dwelt in obscurity, but performed the greater work – and so it is with Mary Adela Blagg, one of the few women of science honoured by a crater on the Moon. The crater is a small one but, given her efforts in resolving crater names, it’s a most appropriate honour.

Mary Blagg was born in 1858, yet lived until 1944, through perhaps the most remarkable time in all Science. Self-taught but for an extension course in astronomy around 1900 she decided, at her tutor’s suggestion, to work on resolving problems of lunar naming (nomenclature). In 1906 she was elected a Fellow of the R.A.S having published papers on lunar features as well as variable stars, the first woman to be so honoured.

When Riccioli in 1651 assigned names to the Moon’s major features he had the field mostly to himself, but by the end of the nineteenth century as telescopes improved and lunar astronomy flourished chaos reigned, with various workers using a range of names for ever more lunar features – leading to Blagg’s efforts to create a standardised list. In addition Wikipedia tell us “she performed volunteer work with Belgium children in WW1 and was fond of chess”(!). Her obituary describes her as of “modest and retiring disposition, in fact very much of a recluse”.

“Chuck” Wood’s (“Modern Moon”) view of Blagg is slightly different: “Do you lack basic drafting skills? So did Mary Blagg back in the 1930’s, but she pencilled the official lunar map for the International Astronomical Union that was the last graphical word on lunar nomenclature until the mid 1960’s when the System of Lunar Craters replaced it.” (LPOD 2009 July 25). Moon watchers should get a copy of Ewen Whitaker’s marvellous “Mapping and Naming the Moon” for the more detailed story of Mary, her work and her poor drafting!

Close to Blagg in Sinus Medii is crater Bruce, named for science benefactor Catherine Bruce – a person as ‘private’ as Blagg – but with a remarkable connection to modern astronomy, that we will consider in a future piece on women of science memorialised on the Moon.

Blagg’s crater may be small but it’s sited near the centre of the Moon’s visible face with no nearby craters for company except Bruce. To help locate it I show larger craters Triesnecker and Chladni in my sketch – and Triesnecker is the focus for a well-known system of lunar rilles (rimae). Crater Blagg is 5km diameter and sits on a prominent mare ridge, part of the valley-like depression (dotted in Fig) in Sinus Medii (the Central Bay) that intersects with Triesnecker. From the NW sharp ridges protrude into S. Medii – I have not detailed them – and as they are aligned towards Mare Imbrium they may have been sculpted by that titanic impact. As crater Blagg dates from the Imbium epoch it’s a well preserved feature. 50 km NW is a possible teardrop shaped lunar dome – and with two craters both named for women of science so close together it’s a unique location on the Moon.

Moon watching – it’s history tapping us on the shoulder!

Harry Roberts, Sun and Moon observer and member of the Sydney City Skywatchers

Harry thinks the big sunspot AR 11024 means the Sun is waking up

Twelve spots without penumbrae that appeared on 4 July 2009. Several “tuned” filaments and short-lived surges can be seen. Drawing Harry Roberts

Long expected solar cycle 24 has been very, very slow out of the blocks – prompting revised predictions for when and how strong the peak of C24 will be.

The first sunspot of C24 emerged in the north in 2008 Jan 2, and the first southern one arose in 2008 May 3 only four months later– both were tiny. The first big spots in the north appeared in Oct/Nov’08, and the first big southern spot has just appeared, 8 months later! And this first big one of the south was a real beauty! In fact it was larger in area, more complex magnetically, and had bigger flares than its earlier northern kin.

Active region 11024 (AR1024 for short) was first noted as a spotless patch of bright faculae near the sun’s east limb at –29, ln. 250 on July 1 at 03:27UT. There were still no spots on July 3 but a small dark filament and some plage were recorded in H-alpha, and Mt Wilson had increased surface field at the site – AR 1024 was emerging!

Frantic days followed logging the rapid rise of the group with rain and cloud aplenty. Flares occur as spots emerge (Zirin tell us), and the jump in GOES X-ray flux was sudden and large – the strongest rise in X-ray background for ANY C24 group so far. Flaring in 1024 reached GOES C2 the strongest for any C24 group to date.

Twelve spots without penumbrae appeared on July 4 in a compact cluster ~3º in diameter, and many flares up to GOES B7 erupted during the day – almost continuously. Several “tuned” filaments and short-lived surges were seen – Figure 1 shows some of these (all in H-alpha), none were > visual class 2F.

Six views of the compact group AR 11024. Drawing Harry Roberts

Figure 2 records five views of the group in WL and Fig 2.3 shows H-alpha detail of July 5 during a B7 flare. Rapid change in the shape of filaments was recorded and repeated surges – mainly along the boundary between p and f polarities as shown by Mt Wilson’s Babcock magnetograph.

AR 1024 reached umbral fields of V23, R24 – stronger than AR 1008 (Nov ’08) with V23, R22. Fig 2.6 shows bright faculae seen on July 9 when the group became more active after earlier weakening (Fig 2.4 and 2.5)

Given the persistent decline of umbral fields noted by Livingston W et al throughout C23 , these latest measures show a rise in C24 umbral field strength – an unexpected turn for a southern group, where C24 activity has been so quiet up until now.

Harry Roberts (Sun and Moon observer and member of the Sydney City Skywatchers)

Harry observes a proto-sunspot on the enigmatic spotless Sun

Proto-sunspot AR 11017, drawn by Harry Roberts

“The Sun is behaving in an unexpected and interesting way” said NASA’s Dean Pesnell in announcing yet another prediction for solar cycle 24 on 2009 May 29, adding “It turns out that none of our models were totally correct”. Whatever the prediction for the new cycle, sun-watching has never been this exciting; let me suggest why.

In old cycle 23 (C23) the sun “chose” to put much of its energy into solar flares – producing the strongest flares for thirty years, maybe for 100 years. Then, perhaps not surprisingly, it plunged into the deepest minimum for 100 years (i.e. since 1911).

And now, well into this deep minimum, we see some unusual activity on our star, activity perhaps last seen in 1911. In particular we have begun to see large faculae regions (FR) appear that are almost spotless. During normal solar activity large faculae regions evolve closely with major sunspot groups – with all authors noting one exception, the tiny spotless faculae at the sun’s poles during solar minima (the polar faculae).

NASA dubs the current large faculae regions “proto-sunspots” and speaks of them as “spots trying to emerge”. None of my texts (ranging from Bray to Zirin ) remark “proto-sunspots struggling to emerge” – and while much is known of faculae generally, these FR are perhaps “new” to solar science. Maybe they were common during that last deep minimum in 1911 – and have been forgotten in the modern literature?

They would be hard to interpret were it not for Livingston and Penn’s “Sunspots May Vanish” paper, first deemed “controversial” but now looking plausible. Is it possible that the FR are in fact normal C24 sunspots but their umbrae are too warm to be visible against the bright photosphere –as predicted by the above authors to occur in 2014 – but well ahead of schedule?

Many attributes of a normal sunspot region (AR) are present in these regions e.g. conspicuous bright faculae, with plage and filaments in H-alpha Flares erupt in them, but without strong spot fields the flares do not exceed GOES B-class, and the faculae seem to spread across wide areas. Yet only a few tiny spots or none at all emerge in the faculae regions (Fig1).

Several C24 “proto-sunspot” regions have occurred, I’ve counted six , the biggest and most recent being AR 11017. First seen May 11 as a very large patch of bright faculae 25º behind FR +22/218 (second rotation AR 11015), the new spotless FR was centred at +19/192 but covered 13º in both latitude and longitude – a faculae region about 5000 area units in size! Next day a single small spot arose at +18/194, with filaments and plage, and on the 13th a remarkable sight occurred. A grey smudge was in good seeing shown to be sixteen tiny spots in two tiny clusters about 5º apart, embedded in bright plage and tangled filaments. The clusters were seen next day, now 6º apart with 8 to 10 tiny spots – but hard to see.

The magnetic polarity of proto-sunspot AR 11017, drawn by Harry Roberts

Mt Wilson digital magnetogram for May 13 shows the extent of the faculae (with fields of ~10G) and with concentrated stronger field coincident with the two spot clusters of about 150G. In fact the magnetogram gave the strong impression that the group was a large bipolar sunspot pair with umbrae about 6º apart (Fig2). Mt Wilson’s Babcock magnetograph showed umbral fields in the two clusters of 1700G – just 200G above invisibility at 1500G.

I suspect this record (of 13th) resolved individual magnetic flux “ropes” each about 1000km diameter separating at the sun’s surface (photosphere) –only some having fields strong enough to appear dark. More normall umbral fields (~2700G say) would have caused large dark p and f umbrae to form instead the tiny spots. This was a memorable observation, and I suspect we are watching sunspot slowly umbrae fading from view as the “Spots May Vanish” authors suggest –events that are unfolding ahead of schedule, for unknown reasons.

By email I suggested to Livingston that these regions (FR) are like Alice’s Cheshire Cat, with only the “smile” (the faculae) remaining once the “cat” (sunspot umbrae) has faded. He liked the analogy and advised he had a week coming on the McMath-Pierce solar telescope shortly. May he have some sunspots to measure.

Magnetic field strength for solar cycle 24 sunspots, drawn by Harry Roberts

Mt Wilson has reported umbral fields for 14 of the 17 C24 groups that have so far emerged. Plotting these fields (Fig 3) shows very weak levels in the first 4 groups (2008), rising to a modest peak of ~2300G in AR11008 2008 November. From there (2009) fields have declined with each new C24 spot group – in line with the Livingston-Penn prediction – and of the six C24 faculae regions seen so far three have been spotless. Currently umbral fields lie just above invisibility (at ~1500G). Note the authors’ published graphs show a steep zig-zag in measured field – with a steady decline only when averaged, so perhaps we are in a short-lived “trough” and values may partly recover to fall again. – but current events seem to confirm, amazingly, that sunspots ARE in fact vanishing.

Harry Roberts (Sun and Moon observer and member of the Sydney City Skywatchers)

Award to Sun watcher and Sydney Observatory volunteer Monty Leventhal OAM!

Diagram of the Sun on the morning of Monday 8 June 2009 (Australian time) drawn by Monty Leventhal OAM. Though there are no sunspots, 10 prominences are shown scattered around the edge or limb of the Sun

Previous readers of this blog would be aware of the work of amateur astronomer and member of the Sydney City Skywatchers, Monty Leventhal, as his full disc drawings and digital images of the Sun are regularly used on this blog. Examples are shown in this post. Monty has received awards previously from international astronomical organisations, but now his work has been recognised by the wider community.

“Digital filtergram shows a nice Prominence on the SW limb reaching an approximate height of 56,000 km”, taken on 16 May 2009 at 22:25 UT, image by Monty Leventhal OAM

I was most gratified to see in this morning’s paper that Monty was included in the Queen’s Birthday honours list. He received a Medal (OAM) in the General Division of the Order of Australia. The citation reads “For service to science through volunteer roles at the Sydney Observatory.” Congratulations Monty!

As indicated by the citation he not only observes the Sun on a regular basis, but he has also been volunteering his time to share his passion for the Sun with visitors to Sydney Observatory. You can meet him at the Observatory and look his telescope on every second Sunday.

“Digital filtergram shows a very active Prominence on the NE limb”, taken on 22 April 2009 at 23:15 UT, image by Monty Leventhal OAM

The OAM to Monty is gratifying not only because it recognises his long standing dedication, but it is also a recognisition for the work of amateur astronomers. As the first amateur to be recognised (I am happy to be corrected on this), I hope that Monty will be the trail-blazer and there will be recognisition for many other deserving amateurs in the future.

Well done Monty!

Views of the Sun by Monty, Deirdre and James Cook in 1869

Drawing of a sunspot on 14 April 1869 by James Cook

While working on a new catalogue for the library of the Sydney City Skywatchers, an intern found an intriguing album of ink and pencil astronomical drawings. They are mainly of Mars at its 1879 opposition and Jupiter from 1869 to 1879. Plus there is the sunspot drawing above. That drawing indicates a complex sunspot group such as probably would have been seen often during that year of solar maximum.

The sunspot drawing and some of the others are signed by James Cook. I have not previously heard of an amateur astronomer by that name and certainly he would not be Captain James Cook who had been killed in Hawaii in 1779. The mysterious Mr Cook appears to have used a number of telescopes as some of the Jupiter drawings indicate a “10″ Metallic Newtonian” while others say “Aperture 15 inch”.

Active Region 1019 on the Sun visible on 2 June 2009, drawn by Deirdre Kelleghan

Amateur astronomers are still drawing and imaging the Sun in 2009 although the Sun is currently in a state of exceptionally low activity. Above is a recent drawing by Irish astronomical sketcher Deirdre Kelleghan who twitters. She says of the drawing:

We are having an unusual few days of hot hot sunny sun , so a bit of solar observing was just the ticket for relaxing in my garden.

Active Region 1019 June 2nd 2009
PST 40 mm / 8mm TVP Up scaled by eye
Pastel, and Conte on black paper
11:00 UT

A prominence on the Sun imaged on 29 May 2009 (Australian date) by Monty Leventhal

Monty Leventhal of the Sydney City Skywatchers is another diligent solar observer. He says of the above digital image:

Today’s Digital filtergram shows a Prominence reaching an approximate height of 84,000 km.

Date:- 28-5-09
Time:- 22.25 UT
Conditions:- Good but very cloudy
Supported by the Donovan Astronomical Trust, Sydney. Australia.
Camera:- Canon 300D
Filter:- DayStar T-Scanner. 6Å.
Telescope:- Meade S.C. 10 inch

Over the next few weeks we will look at more of James Cook’s rediscovered drawings.

Harry warns that the Sun may have lost its spots

The Sun on 30 March 2009 with no spots, image courtesy SOHO/MDI

Sunspots may vanish is the eye-catching title of research by solar physicists Bill Livingston and Matthew Penn last year. Using sunspot field strengths and temperature data collected with the McMath-Pierce solar telescope they discovered systematic changes in both parameters that predict a spotless sun in 2015. Sunspots appear dark on the sun only because strong fields within the flux-rope from the sun’s core maintain a low temperature within the spot, so spots seem dark compared with their surroundings.

The important thing about the “Spots may vanish” paper is that extrapolation from the data shows field strengths dropping below 1500 gauss by about 2015. “So what?” you may ask, but we know when fields get this low spots are no longer seen – that is, they vanish.

The researchers remind us of the Maunder Minimum of the 17C when records say the Thames froze solid on a regular basis, and no sunspots were visible for decades. And the “Spots may vanish” paper suggests a similar event is possible!

Now, I am no “Chicken Little” alarmist, but two unexpected recent events support Livingston and Penn’s prediction, as I’ll briefly describe.

Solar flares over the last ~30 years

In “big picture” terms the sun has had two major anomalies over the past decade. The first anomaly is that flaring over Cycle 23 (C23) was much stronger than the two previous cycles, and anti-correlated with the sunspot count . That is, although the spot count strongly declined from C21 to C23, C23 had much stronger flares than the two previous cycles; an anti-correlation (Fig 1). Also these strong flares occurred over a much longer period than in the earlier cycles; C23 flaring peaked around 2003/4.

The second anomaly is that solar activity, as expected, has declined to solar minimum, BUT this is proving to be an unusually deep and prolonged minimum. In fact the current minimum is the deepest since 1913, the deepest for almost one hundred years.

The two events I believe are closely linked. It’s as if the sun, having had a “giant party” (i.e. hosted so many big flares), is now having a giant “hang-over” and does not want to get out of bed!

The trend in magnetic fields observed on the Sun

As a result, while we have had some new C24 activity, it’s much weaker than any solar modellers predicted. So weak in fact, that I am prompted to think it’s evidence that Livingston and Penn are correct. On their plot the last data recorded was in 2006, when maximum sunspot fields stood at 2300G, and their extrapolation has fields down to 1500G by 2015 (Fig 2). BUT it’s already 2009, and (if they are correct) spot fields will by now have weakened to about1900G. Is this the reason why new cycle activity appears to be so weak?

Of course all attempts to model solar activity involve extrapolation: i.e. predictive modelling is perilous. Can we really expect a spotless sun five years hence? Maybe. And remember all climate on Earth is driven by the sun (if we don’t count minor volcanism and CO2 effects) and with below par solar activity maybe the Gulf Stream will flow only fitfully: and maybe, just maybe, “sunspots may vanish”!

Keep a close watch for sunspots – it could be your last chance to see one!

Harry Roberts (expert Sun and Moon observer and member of the Sydney City Skywatchers)