Author: Peter Anderson

Saturn in 2024/2025 – the rings edge-on

Published: 12 December 2023
Written by Peter Anderson

by Peter Anderson

Approximately every 15 years, Saturn’s rings are presented edgewise as the Earth and the Sun pass through the plane of the rings. In the planet’s 29.4 year orbit, we first see one face of the rings and then 15 years later the other, after passing through the plane of the rings. As Saturn has an elliptical orbit, these edgewise presentations alternate at intervals of approximately 13.75 and 15.75 years.

Saturn showing tilting ringsSometimes there are two extra passages through the ring plane by the Earth as it whizzes from one side of the Sun to the other in six months first above and then below the Sun-Saturn plane and the angles change, and this is the reason for the three passages. For example, when the edge on phase occurs close to Saturn’s solar conjunction as in 2025, the rings are edge on to the earth only once. When the edge on phase occurs near opposition, the rings are edge on to the Earth three times. One ring plane crossing occurs close to opposition, the other two occur close to quadrature, but the Sun passes through the ring plane only once.

Now is the time to consider how you would like to observe these coming events in 2024 and 2025 as the rings narrow. I have used data from Jan Meeus (Astronomical Tables of the Sun, Moon, and Planets). On this next occasion the Earth crosses the ring plane on 23rd March 2025 when Saturn will be only 9.5 degrees from the Sun. The Sun then crosses the ring plane from North to South on May 6th 2025 and Saturn is then 47.5 degrees distant in the morning sky.

Saturn will be unobservable around the time of ring passage that occurs as it has just passed conjunction with the Sun on 12th March 2025. So some very interesting phenomena will be missed when the rings disappear for at least a day or so. Either side of this event the rings are seen incredibly foreshortened and appear as spikes either side of the planet. Over this period with very low and then backlit illumination until 6th May, the rings may well appear very patchy with brighter and darker areas. Their shadow may even be all that is visible as a dark line across the planet.

Though observations will not be possible at the time of the Earth’s ring plane crossing, many of the unusual related effects would be expected to continue until after the Sun has also crossed the ring plane in early May. Saturn is then in the pre-dawn sky but less than 50 degrees from the Sun so the window for good observations at such low altitudes in the morning sky is probably just an hour or so. Nevertheless we are fortunate that the relative positions are favourable and in early May at our latitude Saturn rises to be nearly directly over the sunrise position. This ensures an acceptable altitude for early morning observations. Without the obvious rings as a distraction it also presents an opportunity to clearly see that the disc of Saturn is much more oblate than that of the other giant planet, Jupiter.

But in 2024 Saturn’s rings also provide interesting opportunities. Due to the dynamics of the relative movement of the Earth and Saturn during 2024, the rings will at best come within 1.9 degrees of edgewise around 25th June. One phenomenon reported at the low angle of presentation of the rings (as will occur in mid 2024) is the possible occurrence of transient radial spokes in the rings. Of course many of the phenomena being described require good conditions and moderately high magnifications to be fully appreciated. Saturn then comes to opposition with the Sun on 8th September 2024.

Then in 2025 Saturn is in opposition on 21st September, and aside from the ring plane passages earlier in the year as previously described, Saturn’s rings close to less than 0.4 of a degree of edge on between 17th November and 1st December 2025 . You can easily use the Stellarium Computer Programme to check the appearance. Also refer to the attached plot. Because, in this case the planet was in opposition only two months earlier, this period in late 2025 will be very suitable for convenient evening observations of the nearly edge on rings. Though the angle of the rings will be very low, they will be bright because the angle of the Sun is higher.

Saturn ringless, or with very thin rings presents great satellite observing opportunities with the moons strung out in a line each side of the planet and passing close to and at times even occulting/eclipsing each other. The four major Jovian Moons have apparent diameters between 1.0 and 1.7 arc seconds (Europa 1.0”, Io 1.2”, Ganymede 1.7” and Callisto 1.5”) that can be resolved as discs. However of Saturn’s moons, only VI, Titan, second only to Ganymede in size, but at a much greater distance, displays an observable disc. This is around 0.8 arc seconds in diameter and therefore requires a 6” (15cm) aperture telescope or greater to comfortably resolve as a disc.

The next two largest moons of Saturn only subtend a quarter of an arc second so any hope of resolving any further discs can be dismissed. However transits and video imaging of four of these – Enceladus, Tethys, Dione, and Rhea – have been observed and conducted with very large amateur instruments but the observations have generally been described as ‘very very difficult’.

In my view one of the most satisfying observations has been that of a shadow transit of Titan when the moon and its shadow (of the same approximate size) pass together over the surface of Saturn taking several hours to do so. My predictions using the Occult computer program list eleven of these shadow events potentially partially visible from Eastern Australia. These commence on 28th March 2025 and end on 4th September 2025, but each is concluded before the rising Saturn has reached more than a few degrees in altitude as seen from the east coast. (The dates are (UT) 28th March, 13th April, 29th April, 15th May, 31st May, 16th June, 2nd July, 18th July, 3rd August, 19th August, and 4th September.) They are effectively unobservable from Brisbane at 153 degrees east, and further west in Australia nothing will be seen at all.

I wondered why these events occurred under similar annoying circumstances and the answer is simple. Titan has an orbit of 15.945 days or 15 days 22.68 hours. So for the next orbit of Titan some 16 days later the phenomena would occur just over and hour earlier. The orbit of the Earth around the Sun results in the stars etc. rising nearly four minutes earlier every night. Saturn’s slow orbital motion also tends to work against you and you are effectively back where you started. So the successive shadow events essentially stay put over the six months, ending around the time Saturn rises. However there is a very slow drift and the ending of these shadow transits slowly rises in altitude (as seen from Brisbane), occurring at 1, 2, 3.5, 4.5 and 5 degrees altitude for the last on September 4th 2025.

Of the Titan occultation and transit events involving the disc of Saturn, the situation is more promising than for the shadow events. Again we are constrained by the parameters already described so the events are the latter parts and conclusions of the transits and emergences from occultation. The following events may be observable.
Timings were derived via the Stellarium program that from my experience is quite accurate. No account is taken for limb darkening or any phase effect. (NOTE: Any daylight saving adjustment – if applicable- is not included in EAST times quoted.) I would also suggest commencing a little early in case there is some ‘drift’.

  • 28th March 2025 (UT) 29th March EAST. Transit emergence. Titan’s emerging disc is bisected by the planet’s limb at 5.33am at 8 degrees altitude, and is clear at 5.41am at 10 degrees altitude.
  • 13th April 2025 (UT) 14th April EAST. Transit emergence. Titan’s emerging disc is bisected by the planet’s limb at 5.42am at 22 degrees altitude, and is clear at 5.53am at 25 degrees altitude. *Readily observable
  • 21st April 2025 (UT) 22nd April EAST. Occultation re-appearance. Titan’s emerging disc is bisected by the planet’s limb at 4.20am at 11 degrees altitude and is clear at 4.31am at 13 degrees.
  • 29th April 2025 (UT) 30th April EAST. Transit emergence. Titan’s emerging disc is bisected by Saturn’s limb at 5.08am at 27 degrees altitude and is clear at 5.27am at 31 degrees altitude. *Readily Observable
  • 7th May 2025 (UT) 8th May EAST. Occultation reappearance. Titan’s emerging disc is bisected by Saturn’s limb at 3.25 am at 11 degrees altitude and is clear at 3.43am at 15 degrees altitude.
  • 4th September 2025 Around 7.12pm. Titan grazes the northern limb of Saturn and at this same time its shadow leaves the disc. At only 5 degrees altitude start a few minutes earlier if you have a good horizon but this observation, whilst interesting on the Stellarium program is very marginal at best at such low altitude.
  • 20th September 2025 Transit emergence. Titan’s emerging disc is bisected by Saturn’s limb at 6.22pm at 9 degrees altitude and is clear at 6.37pm at 12 degrees altitude.

Of course the ‘Occult’ program lists many events by the inner moons numbers III, then IV, then V, as the angle of the plane of the rings decreases and then the reverse as they increase again. This occurs between the wider timeframe 20th February 2023 and 2nd April 2027. Centrally to these are the mutual occultations and eclipses between moons ranging from I to V and two unobservable events with satellite VII, and cover the periods between 29th September 2024 and 3rd December 2024, and then between 1st April 2025 and 20th January 2026. However these bodies are quite faint and neither they nor their shadows could be seen in amateur telescopes when projected against the disc of Saturn, nor likely seen when very close to its bright limb. They would simply be faint starlike points passing each other, or in the case of mutual events, merging and separating.

In any case only the brighter ones would be reasonably visible. Their visual magnitudes: I Mimas 12.9, II Encelades 11.7, III Tethys 10.2, IV Dione 10.4, V Rhea 9.7 VII Hyperion 14.2. (VI Titan is 8.3.)

During 2024/2025 several occultations of Saturn by the Moon are predicted to occur for the Brisbane area:

At 9.27am (closest) on May 4th 2024. This is predicted as an occultation by some sources but the edge of the occultation track passes nearly 300km away to the south-east. The 23% illuminated waning crescent Moon will be 53 degrees distant from the mid morning Sun at the time. Because of its low surface brightness and the bright sky, Saturn would be a very difficult object to locate and observe as the northern lunar limb passes close by.

The next is between 10.50pm and 11.47pm on June 27th 2024. The occultation is unfavourable because Saturn is rising in the east and is only 3 degrees altitude when it is occulted. But it is at 16 degrees altitude at re-emergence from behind the dark limb of the 64% waning Moon and this would be readily observable and worthwhile to attempt.

The final occultation occurs between 6.26pm and 6.53pm on September 17th 2024. At first it appears more favourable with an altitude of 20 degrees at commencement at 6.26pm and 26 degrees altitude at re-emergence at 6.53pm. (From my site 10km due west of central Brisbane.) However the Moon is 99% illuminated and the following day is full Moon. Predictions show that both events occur behind the fully illuminated southern polar regions of the Moon. The extremely bright lunar limb relative to Saturn would make meaningful observations/timings very difficult. Further north the event lasts longer and circumstances are different.

There are no lunar occultation events for Saturn visible from Brisbane in 2025.
(Sources are ‘Occult’, Stellarium, and Astronomy 2024.)

The assistance of Dominic Ford (data tables) and Michael Foulkes, Director Saturn, Uranus and Neptune Section, British Astronomical Association, is much appreciated.

Events leading up to the formation of AAQ Mark 1

Published: 30 June 2019
Written by Peter Anderson

Following the upheaval of the division with the Bundaberg group in mid-1964, life settled down and Arthur Page took over the editorship of the ‘Astroquest’ from the departed Vic Matchett.  The next two years were uneventful. The ASQ, as the sole major astronomical body in Queensland, had grown to a peak of 269 members in 1964 on a very much smaller population base than today. The central character was the long-time Secretary, Bill Newell.  He was the official Government observer from the early 1940’s until 1957.  Then Queensland handed over its timekeeping service to the Commonwealth. For timekeeping calibration, he used to time star transits from the roof of the old Executive building.  This included a 4-inch refractor.  The instruments are now in the survey museum.

Bill continued to work in the Survey Office of the Lands Department becoming Assistant Chief Cartographer and handled Government astronomical enquiries. He produced a planisphere for schools and a star chart booklet, and his book, ‘The Australian Sky’ was published in 1965.  He was Secretary of the ASQ from 1942 until his death from a heart attack near retirement on 6th September 1971 on the platform of the Corinda railway station on his way to work. He wasn’t just the Secretary, he was an institution.

The ASQ was effectively run by Bill and Molly Newell. They nominated or at least approved the various key officers and Bill handled all public contact.  One can assume that this was done with the best of intentions to keep things running smoothly, but it dampen individual initiative including proposals for new projects without their prior approval. Things under their stewardship went along routinely and there were few problems, and if routine and uninspiring, management was at least steady and predictable.

But Bill Newell was not an active astronomer and so there was little encouragement from the top to get involved beyond the ‘armchair’ stage. He said, “A 6 inch reflecting telescope was all that was needed to see everything that an amateur could reasonably expect to see”. Observational astronomy did not rank very highly. Nevertheless, in February 1961 the ASQ had established observing sections but these were largely ‘window dressing’ and kept the observing enthusiasts occupied.

There was dissatisfaction within the ASQ, but it was not obvious. I was blithely unaware of any undertones in mid-1966 when I had been ‘tapped on the shoulder’ by Bill Newell to become President.  Beres Page (Arthur’s wife) also nominated and there was an election, which I won by a number of votes being supported, as I was, by ‘the establishment’. I assumed office on 8th July, one day before my 24th birthday. This election was probably not significant merely of itself. Yes, I was President, but especially being very young and inexperienced, I was in thrall to the ASQ establishment.

Arthur and Beres Page had refurbished the venerable 12-inch Eglinton telescope that they were caretaking in their observatory, and they were using it for their variable star research.  However, there was an increasingly strident campaign for access to the instrument ‘at will’ by some ASQ members and this was clearly unreasonable. At the OGM on 12th August the ASQ Observatory Committee was formed and rumblings now began for use of the 12 inch in the proposed society observatory. (The old 18-inch project referenced in a previous article had come to nothing – so was forgotten.)

At a Special ASQ Council Meeting one week later on 19th August 1966, as an apparently unscheduled matter of business, Arthur Page advised he would return the instrument for use in the future ASQ observatory and then did so. He therefore prudently extricated himself from a difficult situation. The telescope was never really used again.  The optics and some fittings are now on occasional display at the Sir Thomas Brisbane Planetarium. (This planetarium likely resulted from an initiative by the Museum Society which had been promoting one for years. It was taken up by the Brisbane City Council, receiving publicity in late 1973, and was completed in 1978.)

The move to establish a society observatory had quickly gathered pace. Plans would include the observatory and support building and a meeting hall and encompassing future ‘full site development’, even a possible planetarium.  The ASQ had made approaches to the Brisbane City Council and on 27th August 1966 the society inspected two potential sites on adjacent knolls at Mt Coot-tha on a spur running off 400 metres further along the road to the West from the lookout (Honeyeater track).  However though having formed an observatory committee, the proposal to ‘get serious’ and establish a building fund was defeated at the OGM on 14 September 1966 by the opposition principally of Bill and Molly Newell.  This led to some dissatisfaction in certain quarters.

In the Newells’ defence, I can at least in part understand their reluctance to get deeply involved in a major project such as an observatory and support buildings.  Given the demographics of the general membership and knowing them, very little would have been achieved as I discovered on a much smaller scale between 1997 and 1999 when I tried to activate our clubhouse with section meetings and extra activities – the clubhouse that had been someone else’s bright idea in the first place.

However, whereas the 18” project in 1963 had started with a £10 slab of plate glass and ‘pie in the sky’ unfocussed plans, this 1966 project had the interest of the Brisbane City Council, and sites had been identified upon which to locate the observatory etc. It had the very definite potential for the Council to be involved and the key supporters within the ASQ included qualified people such as a senior architect Fred Lafferty who drew up provisional plans.

Arthur Page later told me that the failure to establish an observatory building fund was one of the prime drivers leading to the formation of the AAQ Mark 1 in 1969. He subsequently slowly withdrew from participation in ASQ affairs, retiring as Editor in 1967.

I now quote from the first ‘AAQ Annual Proceedings’ (1969) written by Arthur Page: “In November 1966 a nucleus of serious astronomers commenced discussions on the possibility of forming a new-look astronomical organization.  This group comprised Messrs F. and L. Lafferty, Mr J. Van Vegchel, Mrs. Page and I.  We proceeded with caution and deliberation. In the ensuing discussions every factor was analysed, every principle examined in the light of experience gained from an understanding of the local situation, and those existing in other States and overseas…”

Unaware of any of this, when the first year of my term as President was due to expire in mid-1967, I offered to Beres Page that I would not renominate to allow her to stand for the position, at least not opposed by myself. She stated that things had moved on and she was no longer interested. I had simply thought that they were dropping out to concentrate on practical astronomy.

In hindsight, to detail the various factors contributing to the formation of the AAQ Mark 1:

  1. The 18-inch project had stalled a few years earlier indicating a lack of commitment to observational astronomy,
  2. Beres Page’s failed in her bid for election as ASQ President (July 1966)
  3. Increasingly unreasonable demands were made for unfettered access to the restored Eglinton 12” and the instrument was returned to the ASQ (after August 1966)
  4. The ASQ observatory etc. project had stalled for want of demonstrable ASQ support and effort to promote it beyond forming an observatory committee (OGM 14th September 1966)
  5. General intransigence of the ASQ management to change. In this last respect even a number of officers of the ASQ were somewhat uneasy and dissatisfied, certainly by the second half of 1968.

Towards the end of 1968, there were rumours of the formation of an informal practical observers’ club – emphasis on the word ‘informal’.

In January 1969 Arthur Page invited my wife Evon and myself to a meeting at his house in Kellino Street Chermside on 8th February ostensibly to discuss an informal observers’ group.  We believed this was to be a loosely structured group, meeting regularly to discuss observing and observations. The ASQ at that time was largely an armchair astronomers’ forum, with only a few observers.

We were very surprised to be presented with a fully drafted Constitution which was then examined clause by clause. The original name proposed was ‘The Association for the Advancement of Astronomy, Queensland’.  At this meeting the name ‘Astronomers’ Association, Queensland’ was decided upon as more suitable.

Inaugural meeting AAQ Mark 1 – 8th February 1969
Inaugural meeting AAQ Mark 1 – 8th February 1969

This photograph records those present at the birth of the AAQ Mark 1 which flowed seamlessly through to the merger with the ASQ in 1978 to become the present body, AAQ Mark II.  This was the moment of its formal beginning! Perhaps the only people that some older members will recognize are Arthur Page, Harold Powell, and myself. I may well now be ‘the last man standing’.

The Astronomical Society of Australia (ASA), a professional body, was formed at a conference 30th November to 2nd December 1966 a few years earlier. Arthur Page became a member, served on its Council, and ultimately became an Honorary Fellow. (Arthur later also became a member of the International Astronomical Union (IAU) in 1985 and received an Honorary Doctorate (UQ) in 1994. He was president of the AAQ on several occasions and died on 1st February 2011.)

I reference the previously quoted statement from the first AAQ Annual Proceedings in 1969:

“In November 1966, a nucleus of serious astronomers commenced discussions on the possibility of forming a new-look astronomical organization.”

By this time (November 1966), plans for the formation and structure of the ASA as a professional body devoted to the advancement of astronomy were well advanced, and I believe they acted as an inspiration to emulate on a local level.

There were a number of unique features of the AAQ and I will mention just a few: Three classes of membership were created – full, associate, and honorary.  Full members were to be formally qualified or be actually engaged in contributory observational work or research … there was no compromise!  They were the ones who would vote and hold office.

The Constitution was careful to set out the responsibilities of each of the Officers as well as other requirements such as a strict limit to the length of continuous service, considering past experience. The principal provisions, somewhat watered down, largely remain today.

In the original Constitution there was no provision for a ‘Newsletter’ but it included the core functions of the ‘Newsletter’ namely notices to members of forthcoming meetings and minutes. This formed part of the General Secretary’s duties. These started off as simple notices but soon developed into a newsletter produced and dispatched by an overworked General Secretary.  As it developed it first became titled the ‘General Circular’ and from the October 1971 issue has been titled the ‘Newsletter’. The present style AAQ logo first appeared in the November 1972 edition. Currently we have Observing Sections that did not appear in the original constitution – observing activity in the early days being directed towards specific projects, but more of this in my next article about the early days of the AAQ Mark 1.

The first two meetings after formation were held at our home at 7 Hepburn Street, Stafford Heights, where we had a large downstairs room, then at a central city venue, but by mid-year we had settled into our long term meeting venue, the Professional Officers’ Association Rooms at 453 Ann Street, City.

Reflections on the years 1896-1917 by Peter Anderson

Published: 30 June 2019
Written by Peter Anderson

During my investigations I was struck by the many strong parallels between the events of the time and those that occurred in the amateur astronomical community up to a century later. I am constantly reminded of a quote often attributed to Mark Twain “History doesn’t repeat itself, but it often rhymes.”

So these events which unfolded in the Brisbane Astronomical Society between 1896 and 1917 were destined in a large part to repeat themselves over the ensuing century.

One of the main issues is the propensity of certain strong personality types to become antagonistic towards each other. Perhaps each of these active and energetic parties has a different vision and a different manner of pursuing it, and trouble is to be expected if their paths cross.

Sometimes, once a pattern is established, it may cloud rational action. In scientific and other organisations, this has occurred since antiquity. For example the dispute between Newton and Hooke became very vindictive, certainly on Newton’s part.

I am reminded of Julius Caesar (I,ii,140-141), “The fault, dear Brutus, is not in our stars, but in ourselves, that we are underlings.” In this respect it can be interpreted that Fate is not what drives men to their decisions and actions, but rather the human condition. It is within us and not external.

Then, there is the lethargy of the members in failing to support even quite modest initiatives that would benefit the organisation. This lack of support by members of the Brisbane Astronomical Society after its formation in 1896 swiftly led to its effective collapse with a final coup de grace in 1917. This pattern has been repeated.

This may seem very pessimistic but there is also an upside. Often individual members will become very motivated and active. But equally as often they burn out after a few years when, either their interests change, or they realise that little lasting is being achieved. There are those of course who plod on in a steady fashion over decades, but the average membership lasts merely a few years.

Acknowledgements (for events 1896-1917)

Published: 30 June 2019
Written by Peter Anderson

The research by Steve Hutcheon into the history of various large telescopes in Queensland in the late 19th and early 20th centuries prompted my interest in the subject. His continued dogged research has provided much of the background for this paper which I hope provides a balanced historical perspective. In many respects I am merely piecing together his research into a chronological account.

I also acknowledge the assistance of Mr W. Kitson, now retired and Former Senior Curator, Queensland Museum of Lands Mapping and Surveying. Other material has been derived from the astronomical historical papers by Professor Wayne Orchiston, and finally I express my appreciation to the State Library of Queensland for the assistance rendered by their researchers.