Harry observes the strange morphing sunspot group AR11089

The sunspot group AR11089 as it first appeared on the east limb or edge of the Sun. Drawing. Drawing and copyright Harry Roberts ©, all rights reserved

AR11089 is not the name of an underground rock band, but the label applied by the US NOAA organisation, charged with keeping track of sunspots – as counting spots is still the key way of comparing solar activity across the centuries. Was the sun really spotless during the 17th century? Was its activity in the mid 20th century a four hundred year peak? Such questions are answered mainly by looking at the sunspot count.

The second half of the 20th century was the age of satellites; they imaged the sun in a range of wavebands particularly EUV (extreme ultraviolet). But satellites have short lives (one was even ‘shot down’ by the USAF) and normalising their data with the classic spot count isn’t easy. In fact, the best view of any sunspot is still the one in your trusty 3” or 4” amateur ‘scope with an aperture filter!

While this is titled AR11089 I want to briefly recall AR11085 – the spot group that “nobody saw” (except NOAA and the lucky writer). This small bipolar group perhaps lasted less than ten hours, and then disappeared – but when its locality next returned to the sun’s east limb, there was a large active-looking spot group at the exact site. And now everyone could see it, renumbered AR11089.

There are several odd things about this new group, apart from its Lazarus like reappearance. It’s roughly triangular in layout while most spot groups are bipolar and align E-W on the sun. And AR11089 sits in a large area of faculae (WL) and plage (Hα) that has another such activity patch only a few degrees west of it; this latter area is void of spots. Are they related in some way?

Solar Dynamics Observatory views of sunspot region AR11089, annotated by Harry Roberts

They are; the new SDO satellite views show magnificent arches (field transition arches) connecting both plage regions – the whole being one huge magnetic entity (Fig 3, main spots arrowed). And yet while fields within AR11089 briefly reached a ‘strong-ish’ 2500G the group has produced no flares >GOES C1. Curiously it also has few of the usual dark active region filaments (arf) that attend even the smallest sunspots.

The writer first saw the group at the east limb early in its development amid brilliant faculae – having six spots, the largest sited at –21/204 (Fig 1). The Fig shows changes from 19th to 21st (UT) – the group developing substantial penumbrae and ten or more umbrae, still in a triangular layout.

Sunspot group AR11089 on 23 July 2010. Drawing and copyright Harry Roberts ©, all rights reserved

Twenty-four hours later saw an increase to 20+ spots, with many tiny ones in short chains. The preceding spot (p) had a field of R25G (red 2500 gauss) and the larger following (f) spot to the SE had V24. Both are strong fields; but the trailing spot of the ‘triangle’ was now fading, with a few small spots in a chain. Overall the group seems to be ‘morphing’ into a more conventional E-W arrangement, and the remaining (p) and (f) components with 6º N-S separation may soon feel the pull of the Hale-Nicholson force and undergo some dramatic rearranging.

Harry Roberts is a regular contributor to this blog and a member of the Sydney City Skywatchers.

Harry sees a short-lived sunspot group – AR11085

Sketches of short-lived sunspot AR11085

These are strange days for sun watchers: many emerging spots are faint and short-lived – some last less than 24 hours; here today, gone tomorrow! ‘Old hands’ suggest we are still in sunspot minimum – but most measures of activity show a slow rise from the deep deep minimum of 2008 –2009.

A good example is AR11085, that was briefly seen on June 29 when the 4”’Mak.’ (white light) was pointed sunwards. The large single spot AR11084 was clear to see on the sun’s disc – and well west of it a small bipolar spot cluster was visible too –“AR 11085?” my log suggests. Nobody else reported this new group – Monty saw nothing at the site only 5 hours earlier; Mt Wilson’s 150’ ‘scope had nothing 18 hours before. Timings sited the new group at –23/203; I expected the Net would soon bristle with reports.

I was to be disappointed; apparently nobody else saw the new group. And on June 30 I was surprised when it got a NOAA active region number AR11085 – clearly someone had seen it! (Sadly, NOAA does not reveal its sources.) Next day Mt Wilson reported one tiny spot at the 11085 site, with a weak umbral field of R17 (i.e. red 1700 gauss. Remember, around 1800G is the minimum for visibility).

Since the group had not been seen by Monty L six hours earlier, and when logged by Mt Wilson ten hours later, had almost gone, it seemed that AR11085 had had a very short life indeed.

Timeline of observations of short-lived sunspot AR11085. Drawing Harry Roberts

To get an Active Region number a spot has to last at least 24 hours – shorter-lived groups being so much statistical ‘noise’. How long did AR11085 actually last? Presumably NOAA knew it had a life of over 24 hours – at this point a timeline was created to find the probable lifetime of the group (Fig).

The timeline plots observations both negative (not sighted) and positive (sighted) for the spot group by the following: MtW is Mt Wilson’s 150’ solar ‘scope; ML is Monty Leventhal; HR is the writer; and NOAA the well-known US Authority.

Although Solarmonitor’s website asserts the group persisted through June 30th, the evidence (MtW) shows it was almost gone by 14:15UT on the 29th – and its persistence through the 30th is unlikely. Unless other records can be added we may conclude that AR 11085 lasted less than 24 hours – say 18 hours. Perhaps the group should not have gained a NOAA active region number – and it illustrates one of the challenges now facing sun watchers: recording current sunspots before they disappear!

Harry Roberts, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers

Ella reports on observing the stars from the South Pole

Dr Ella Derbyshire at the South Pole, image courtesy United States Antarctic Program

Alan Plummer: This winter Ella Derbyshire is at Amundsen-Scott South Pole Station where she is the station’s physician. The station is right under the South Celestial Pole at an elevation of 2,835 meters. On this trip – not her first – Ella had the thought to take binoculars with her for some stargazing. More to the point, Ella expressed an interest in doing some useful astronomy. As variable stars are the subject of active research and many are within the range of small binoculars I had the pleasure of sending of a set of charts and a choice of targets. Ella has since joined the VSS and the AAVSO and writes this report on what it’s like to observe where the Sun never sets. Over to Ella:

The bottom of the world is an interesting and challenging location for a novice variable star observer. Because the winter scientific research at the South Pole requires dark skies, we make conscious efforts to avoid light pollution. There are just enough thoughtfully-placed red lights outside to guide people from building to building as they walk through the dark. All our winter vehicles also shine only red lights. Once we arrive at astronomical darkness, our only two significant sources of light pollution are the moon, which rises monthly and then remains above the horizon for a fortnight, and auroras, which can be surprisingly bright and are far less predictable than the moon.

The map of the South Pole night sky is the map of the South Celestial Hemisphere. With the South Celestial Pole directly above us, and the Celestial Equator as our horizon, the star patterns are always in the same orientation, and so they are easy to learn. Stars do not rise or set here, they simple circle around us, inching a little bit westward with each passing day. With this simple arrangement, once I find a star in the sky, finding it again, assuming that it remains bright enough to find again, is easy.

I can choose any hour of the day for observations. Because target stars are always above the horizon, and the sky is as dark at noon as it is at midnight, the time of day that I choose to observe is not especially important. I just locate my guide stars, and then start star hopping.

Observing variable stars from the South Pole requires a bit of preparation. The coldest weather brings the clearest skies. Whenever it warms up, there is a persistent wind blowing, picking up the snow and tossing it in front of the stars. By the time that the temperature reaches -40ºC, the wind, which can reach 40 knots on warm days, is creeping up coat sleeves and under facemasks, threatening any inadequately covered skin with frostbite. Fortunately, staying outside to watch stars is pointless at such times because in polar wind storms, even Sirius and the moon are hidden. During cold, calm weather, with the temperature from -60 to -70ºC, dressed in a full set of extreme cold weather gear, I can stand still for almost an hour at a time, gazing up at the sky. If I get dark-adjusted before I venture out into the cold, I can make the most of these observing sessions.

In addition to chilling the observer, the cold affects whatever tools we bring outside. I record my results in pencil because ink freezes. Camera batteries die quickly, making astrophotography a real challenge. Camera lenses, eyeglasses and binoculars frost over with any misplaced breath, and must be warmed and dried to be useful again. It helps to be efficient at locating the target stars and comparison stars and at recording the results. After a while, even eyelashes frost up and will eventually stick together, providing an unambiguous clue that it is time to return inside.

Dr Derbyshire’s report was forwarded by Alan Plummer, prolific and expert variable star observer and a member of the Sydney City Skywatchers

Alan talks about the Mira type variable star R Hydrae and tells how to observe it

A finder chart for the variable star R Hydrae, prepared by Alan Plummer from a Sydney Observatory star map.

This is the second in a series of posts on variable star observing, following the recent one on Eta Carinae.

Throughout this 2010 autumn and winter a star will be slowly brightening from the darkness only to become unobservable in the evening spring twilight just as it gets to naked eye brightness. The star is R Hydrae, and I’ve marked its location on the finder chart above made from the Sydney Observatory Sky Map. The coincidence of being in conjunction with the Sun at maximum light is temporary; because this star pulsates with a period of around 388 days, the blind spot drifts across the star’s cycle as the years go by.

R Hydrae is a Mira type variable, which is defined as being a pulsating red giant changing in brightness by more than 2.5 magnitudes over a period longer than about 90 days. R Hya is on the AAVSO ‘Legacy’ list of objects, meaning that they have a century or more of observations in the International Data Base. See the light curve pictured below. Such a span of observations can tell a story; but this one starts even further back than 100 years…

Observations of R Hydrae, courtesy of the AAVSO, used with permission

The first and best of the ‘modern’ European star atlas’ was Beyer’s Uranometria, compiled in 1603. This did not mark R Hya, but it was later plotted on Hevelius’ version in 1690. In 1669 a man called Montanari, who had Beyer’s 1603 atlas, noticed the star, and thinking the 1603 atlas in error, marked it on his own copy. It was a bit of bad luck he didn’t suspect a variable, as Montanari himself had already discovered one variable star – Algol (beta Persei). The nature of the star still remained undiscovered. To quote from Kerri Malatesta of the AAVSO:

Montanari’s marked atlas later came into the hands of Giacomo Maraldi…whose curiosity about the addition brought him to the field of R Hya in 1702. Using Montanari’s positional reference, Maraldi tried, without success, to identify the star. Intrigued by the mystery, Maraldi continued to monitor the area until 1712, noting maxima of the star in 1704 and 1708 and hence its variable nature.

Now to the story such an observational history reveals: a study has found that the pulsation period has declined from 495 to 380 days between around 1700 and 1950, and the amplitude has changed considerably. Recorded maxima have been observed as bright as 3rd mag and as faint as 6th. And the minima have been seen from 9th to 11th mag.

The most likely explanation for the changing nature of this pulsating star is that it had a so-called thermal pulse just before 1700. This is when a shell of burning hydrogen near the core accumulates enough helium in a shell below it to ignite that helium, in a flash, and in so doing extinguish the hydrogen shell. All this is wrapped around an inert carbon oxygen core. The idea is that changes within the star effect changes in the visible envelope, and how that behaves.

Chart and sequence for R Hydrae, excerpt from VSS RASNZ chart 12B, by Mati Morel

So if you want to join in the study of this star you’ll need 7×50 binoculars and/or a 4 inch telescope, and use the chart and sequence above in the same way that was described in the blog post on Eta Carinae. Observe this star once a fortnight and keep your observations on file; my next blog post will be about the agencies that collect and distribute the observations, and how you can use can those agencies. Or you can go to the AAVSO website now and do that yourself!

Acknowledgement: This post has used Malatesta’s work R Hydrae, May 2002 Variable Star Of The Month, which is recommended for further reading.

Alan Plummer, Sydney City SkyWatchers

Another award for Monty Leventhal OAM – the Steavenson Award of the British Astronomical Association

Monty Leventhal in full flight talking about his solar images. Image Nick Lomb on 2 May 2005

Monty Leventhal OAM is a keen amateur astronomer whose images and drawings of the Sun have often been featured on the pages of this blog. Recently his work was recognised by the award of a Medal (OAM) in the General Division of the Order of Australia. Now he has received another award for his careful and conscientious observations of the Sun for almost two decades – the Steavensen Award from the British Astronomical Association.

The Steavensen Award is in memory of Dr William Herbert Steavensen (1894-1975) a medical practitioner who was a lifetime astronomical observer. He was such a serious observer that he was allowed to use professional instruments such as the 71-cm Grubb lens telescope at Greenwich Observatory and the world’s largest lens telescope, the 102-cm, at Yerkes Observatory near Chicago. Moreover, he served as President of the prestigious Royal Astronomical Society from 1957 to 1959.

The citation for the award states:

This award shall consist of a book whose value shall decided by the Council; its cost shall be met from the general funds of the Association.

It shall be awarded to a member who has made an outstanding contribution to observational astronomy.

Previous recipients have included in 1993 Harold Hill who is well-known for his lunar drawings published by Cambridge University Press in 1991 and in 1998 Albert Jones the prolific New Zealand observer of comets and variable stars – he made over 500 000 observations of variable stars, a feat no one had previously achieved. Monty is in good company!

A Hydrogen Alpha image of a prominence on the edge of the Sun on 3 April 2010. Image Monty Leventhal OAM

The citation to the Council of the British Astronomical Association about Monty’s observing work was prepared by myself and Michael Chapman, the President of the Sydney City Skywatchers, formerly the NSW Branch of the British Astronomical Association. Here is an extract:

For the past 16 years on every clear morning Monty has been conscientiously observing and making detailed drawings of the Sun. The drawings record the exact positions of the various activities that do occur on the Sun, such as sunspot groups, flares, filaments, surges and prominences using full aperture white light and H-alpha filters. He has also taken valuable images of the phenomena visible through the H-alpha filter.

He writes up all the data that he collects from his observations and distributes monthly reports to a wide range of relevant groups, the foremost of which is the Solar Section of the BAA. Other groups are: CV-Helios in Norway, the American Association of Variable Star Observers, the Intersol Program in Germany, the Solar Observers Society in Poland, the Royal Astronomical Society of New Zealand, the Association of Lunar and Planetary Observers in the USA (ALPO) and the Astronomical Association of Queensland in Australia. He has received certificate awards from a number of these organisations: AAVSO, ALPO, CV-Helios Network and the Solar Observers Society. Moreover, recognising his expertise, the ALPO commissioned him to write a manual on observations of the Sun in H-alpha and on solar photography; this was completed and published in 2005.

This data is exceptionally valuable as it comes from a longitude from which the Sun is less commonly observed than, say, from the UK. Also because Monty has now been making observations for a fair length of time his observations form a highly consistent and reliable data set.

Congratulations Monty! Keep observing the Sun!

Alan explains how to make your first variable star observation – easy and fun to do

Hubble Space Telescope image of the expanding cloud of gas and dust surrounding the massive star Eta Carinae. To create this image two images taken 17 months apart have been superimposed to highlight the rate of expansion of the cloud. Image courtesy Jon Morse (University of Colorado), Kris Davidson (University of Minnesota), and NASA

This month’s March 2010 night sky map shows many interesting stars, not least of which is the variable star Eta Carinae. You’ll find it plotted half way between the Southern Cross and the False Cross. This star is a dim naked eye object from dark skies, or is visible in 7×50 binoculars from under city lights, and shines from far across the galaxy. This is no near neighbour.

At different times in the past Eta has been both much brighter and much fainter than it is today, depending upon whether it is blowing itself apart with radiation pressure, or being obscured by the stuff it’s thrown off. Look at the above picture by the Hubble Space Telescope; now that everything is ‘awesome’, this star (or stars, it’s a binary system) is hard to describe with words. It’s many times more massive than our Sun and many tens of thousands of times more luminous. The observations of variable star observers are important in studying this fascinating star. Here’s how you do it…

Star chart showing stars in the vicinity of Eta Carinae. Drawing with AAVSO chart plotter by Alan Plummer

Use the Sydney Observatory sky map to locate the general area in the southern sky, and then move to the chart provided here generated with the help of the AAVSO chart plotter. You will need to find the stars in the shape of the ‘7’ with the line marked out to the right of the figure. If you look at the sky map, you’ll see that pattern of stars there too.

This is an important principle; find the field, don’t just look for the target. The numbers on the chart are called the sequence, and they are visual magnitudes of un-changing stars without the decimal places marked. So ‘47’ is a star of 4.7 magnitudes in the visual band. Find two comparison stars that can define the target in brightness. For instance, it may be between ‘46’ and ‘51’. Look directly at the comparison stars one after the other, and judge where between them Eta lies. Do this by dividing 46 and 51 into steps – 46, 47, 48, etc – and write down your estimate, the comparison stars you used, and the time. For example, you may have:

Eta Car, 5.0, using 47 and 51, at 8pm EST

Do this once a week and keep your estimates on file, and in other blog entries soon I’ll describe how and why to make them available to the worldwide astronomical community. If you take the trouble to do this, and make it an ongoing commitment, you’ll be in for a treat…

Alan Plummer, variable star observer and member of the Sydney City Skywatchers

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