RASNZ Electronic Newsletter November 2017

The RASNZ Email newsletter is distributed by email on or near the 20th of each month. If you would like to be on the circulation list This email address is being protected from spambots. You need JavaScript enabled to view it. for a copy. The latest issue is below.

Email Newsletter Number 203

Affiliated Societies are welcome to reproduce any item in this email newsletter or on the RASNZ website http://www.rasnz.org.nz/ in their own newsletters provided an acknowledgement of the source is also included.


1. First Interstellar Asteroid
2. Upcoming Astronomy Camps, Star Parties
3. Treasurer Sought
4. RASNZ Administrative Deadlines
5. Back Issues of Southern Stars Wanted
6. BAA Membership Search
7. Impact of Blue Light LEDs
8. The Solar System in December
9. Variable Star News
10. Solar Storms and Auckland's Damaged Fuel Pipeline
11. NZ's Stargazing Places Reviewed
12. Surprising Science from Cassini's Grand Finale
13. How to Join the RASNZ
14. Email Address Changes, Please
15. Next Newsletter December 16

1. First Interstellar Asteroid

The first asteroidal object from interstellar space has been discovered. Previously only some dust, recorded as micro-meteors, has been known to come from beyond the solar system.

On October 18 the Pan-STARRS 1 telescope on Haleakala, Hawaii, found an asteroidal object moving in a comet-like orbit. It was given the comet designation C/2017 U1. However its orbit was much too hyperbolic, the object was going much too fast, to be comet from the outer edge of the solar system. Also long exposure images taken with the Very Large Telescope in Chile showed that it wasn't a comet. No fuzziness could be seen, it looked totally asteroidal, so it was re-designated A/2017 U1.

The shape of an orbit is described by its eccentricity, 'e'. A circular orbit has an eccentricity of 0. The main planets have orbital eccentricities of less than 0.1 except for Mercury for which e = 0.21. With few exceptions comets have orbital eccentricities near 1. Long- period comets, those taking centuries to return, have orbits shaped like long thin cigars. Their orbital eccentricities are a fraction less than 1.

An eccentricity of 1 is a parabola, a cigar-shaped curve at the sun end but with the inward and outward tracks never closing together at great distances. Comets approaching the Sun from far away move in almost parabolic orbits. A small nudge by the gravity of a planet can easily speed up the comet slightly or slow it down. If it is speeded up then its orbit becomes hyperbolic: it has an eccentricity slightly bigger than 1 and enough speed to escape the Sun's gravity altogether.

Comets that have come from far way often appear to be in hyperbolic orbits when they are near the Sun. This is because, on their way in, they are being accelerated by the combined gravity the Sun and the planets. That makes the gravity pull 0.1% stronger than the Sun's gravity alone. So a comet's orbital eccentricity might be as great as 1.005 when near the Sun but reverts to less than 1, an elliptical orbit, as it moves away from the Solar System and has the combined gravity of the Sun and planets slowing it down.

The most extreme hyperbolic orbit previously observed was that of Comet Bowell (C/1980 E1) which had an eccentricity near 1.05. But that was due to it passing just 0.23 AU, 35 million km from Jupiter and picking up extra speed.

The orbit of A/2017 U1 has an eccentricity of 1.19. To have this orbit shape it must have already been travelling toward the Sun at 26 km/sec when it was first acted on by the Sun's gravity. Before discovery it had passed just 0.25 AU or 38 million km from the Sun on September 9. Given its small size, estimated from its brightness to be around 160 metres, it was lucky to survive the cooking.

Running the object's trajectory backwards in time finds that it entered the solar system from the direction of the constellation Lyra, within ½° of right ascension 18h 44m, declination +34°40'. That's 4½° from the present position of Vega.

More intriguing is the fact that A/2017 U1 is coming from a spot only 6° from the solar apex, the direction that our Sun is moving (at about 20 km/s) through its interstellar neighbourhood and thus, statistically, the most likely incoming direction for an interstellar visitor.

Interstellar asteroids are no real surprise. We know that stars like the Sun form proto-planetary disks during their formation. The stars are also relatively close together in their early stages so close encounters would be common. These would allow outer planets or planetesimals to be removed. The MOA microlensing survey at Mt John has found evidence of several Jupiter-sized planets in interstellar space. Because the space between the stars around us is so big the chance of any of interstellar object, even a small one, coming close enough to be seen is very low but, as A/2017 U1 has shown, not zero.

-- Some bits of the above cribbed from Kelly Beatty's article at http://www.skyandtelescope.com/astronomy-news/astronomers-spot-first-known-interstellar-comet/ The discovery announcement and first orbital elements are in Minor Planet Electronic Circular 2017-U181.

2. Upcoming Astronomy Camps, Star Parties


-- From 'Keeping in Touch' #23, 1 October 2017.

3. Treasurer Sought

Retiring RASNZ Treasurer Simon Lowther writes:

After eight years in the position I will be retiring as the society's treasurer. I am happy that I am leaving the post with the society in a healthy financial position and can see that a new burst of enthusiasm will continue the growth of the last few years.

Please consider giving something back to this society that gives to the NZ astronomical community by putting your name forward at the next conference.

4. RASNZ Administrative Deadlines

February 3 is the deadline for the following: RASNZ Fellow nominations - RASNZ Rule 19 RASNZ Honorary Members nominations - RASNZ Rule 11 RASNZ Murray Geddes Prize nominations - RASNZ By-Law G5 Nominations of RASNZ Officers for 2018-20 - RASNZ Rule 74 Earth & Sky Bright Star Award - RASNZ By-Laws K

Feb 15 RASNZ Section and Group reports due to the Secretary - RASNZ By-Law F14 Mar 15 SWAPA applications deadline (for high school students) - http://www.rasnz.org.nz

-- From Keeping in Touch #24, 18th November 2017

5. Back Issues of Southern Stars Wanted

Leonard Matula, a US collector of astronomical publications would appreciate the following editions to fill gaps in his collection. If anyone can help, please send them to Bob Evans (address below) and he will pass them on. Volume 51 (2012) numbers 1, 3 and 4 Volume 52 (2013) numbers 2, 3 and 4 Volume 53 (2014) numbers 1, 3 and 4 Volume 54 (2015) numbers 1 and 4 Volume 55 (2016) numbers 1, 2 and 3

In addition, if anyone can supply him with earlier editions of Southern Stars, that is Volumes 1 to 50, please contact Bob for Leonard's contact details and further information.

Bob's postal address: 15 Taiepa Road, Otatara, RD9, Invercargill 9879. Email This email address is being protected from spambots. You need JavaScript enabled to view it..

6. BAA Membership Search

Anthony Kinder writes: I am currently researching the membership of the British Astronomical Association (BAA) since it was founded in 1890. Included in this is any and all information I am able to obtain about the person concerned. There are a number of New Zealander's who were members (e.g. Leslie J. Comrie, John Grigg). I would be interested in hearing from any RASNZ member who is or was in the past (or even considering joining in the future) a member of the BAA.

Send replies to Anthony at This email address is being protected from spambots. You need JavaScript enabled to view it.

7. Impact of Blue Light LEDs

The Royal Society of New Zealand has started developing expert advice to summarise the latest evidence on the impact of blue light wavelengths from LEDs. This could cover issues such as the impacts of: - LED screens and lighting on sleep patterns - LED street lighting on the nocturnal environment - blue wavelength light pollution on New Zealand's astronomy. For further information contact Dr Marc Rands This email address is being protected from spambots. You need JavaScript enabled to view it.. https://royalsociety.org.nz/what-we-do/our-expert-advice/our-expert-advice-under-development/impacts-of-blue-light/

-- Forwarded by Steve Butler

8. The Solar System in December

Dates and times shown are NZDT (UT + 13 hours) unless otherwise stated. Times are for Wellington. They will vary by a few minutes elsewhere in NZ.

The southern summer solstice is on December 22 with the Sun appearing furthest south at 5.28 am, about 12 minutes before sunrise at Wellington.

             December  1  NZDT          December 31  NZDT
      SUN:  rise 5.40am, set 8.39pm    rise 5.47am, set 8.59pm

Twilights    morning     evening        morning     evening
Civil:    start 5.10am, end 9.10pm   start 5.17am, end 9.31pm
Nautical: start 4.28am, end 9.52pm   start 4.34am, end10.14pm
Astro:    start 3.40am, end10.41pm   start 3.42am, end11.05pm

December Phases of the Moon (times NZDT, as shown by GUIDE)

  Full moon:     December  4 at  4.47am (Dec  3, 15:47 UT)
  Last quarter   December 10 at  8.51pm (07:51 UT)
  New moon:      December 18 at  7.30pm (16:30 UT)
  First quarter: December 26 at 10.20pm (09:20 UT)

The Planets in December 2018

Of the five naked eye planets only Mars and Jupiter will be far enough from the Sun for viewing and they are in the morning sky. Mars will be the better placed, especially early in the month.

Mercury, Venus and Saturn are all close to the Sun and at best make difficult objects. Mercury and Saturn are in the early evening sky at the beginning of December but reach conjunction during the month.

MARS starts December in Virgo rising more than two hours before the Sun. On the 1st it will be 3° below Spica, the planet being the fainter object at magnitude 1.7 compared to Spica's 1.1. On the 21st Mars will cross into Libra. By the 31st it will rise 3 hours before the Sun

During December Mars will be catching up with Jupiter, they are 16° apart on the 1st but only 3° apart on the 31st.

JUPITER is in Libra all month. It rises just over 80 minutes before the Sun on the 1st. This is close to the start of nautical twilight so Jupiter will not be an easy object low in the twilit sky. By the end of December Jupiter rises more than 3 hours before the Sun, only 9 minutes after Mars. The two planets will be more than 20° up an hour before sunrise, Jupiter more than 3 magnitudes brighter than Mars.

The crescent moon will be some 5° below Mars on the morning of the 14th and a similar distance from Jupiter the following morning, also Vesta will be less than a degree to the right of the moon.

MERCURY starts the month as an evening object setting nearly 2 hours after the Sun. 45 minutes after sunset, Mercury at magnitude 0.0 will be 8° above the horizon towards the west-south-west. On the 3rd of December, the planet is stationary, after which it starts moving to the west towards the Sun which itself will be moving to the east. Their separation will decrease rapidly over the next few days until Mercury is at inferior conjunction with the Sun on the 13th. At conjunction Mercury will pass 1.5° north of the Sun.

After conjunction Mercury will be a morning object. By the end of the month it will rise 85 minutes before the Sun, so will be a very low object a little to the south of east as the sky brightens.

SATURN will also finally disappear from the evening sky during December. On the 1st it will be nearly 3° to the lower right of Mercury, making Saturn even more difficult to see. It is at conjunction with the Sun on the 22nd. After conjunction it too becomes a morning object but will be too low for easy observation rising only half an hour before the Sun on the 31st.

VENUS is close to the Sun all month. It rises 28 minutes before the Sun on the 1st. This reduces to only 11 minutes earlier on the 31st.

Outer Planets

URANUS is in Pisces during December. It is well placed in the evening sky once it is dark. It sets about 1.45 am at the end of December.

NEPTUNE is also an evening object setting about 100 minutes before Uranus. So at the end of December it sets just after midnight. The planet is an Aquarius at magnitude 7.9.

PLUTO, magnitude 14.5, remains in Sagittarius. By the end of December it sets only have an hour after the Sun.

Brightest Minor Planets

(1) CERES is a morning object in Leo, brightening from magnitude 8.1 to 7.5 during the month. (2) PALLAS is in Fornax during December. It dims a little from magnitude 8.4 to 8.7 during the month. (4) VESTA is in Libra during December quite close to Jupiter. At their closest on December 11, Vesta will be about 4° from the gas giant. Vesta at magnitude 8 will rise two and a half hours before the Sun on the 31st. (7) IRIS dims from magnitude 7.8 to 8.6 during December. The asteroid is an evening object in Aries. (8) FLORA is a morning object brightening from magnitude 9.1 to 8.3 during December. It is in Gemini two days short of opposition on the 31st. (20) MASSALIA starts December in Orion at magnitude 9.0. It crosses into Taurus on the 11th, reaches opposition on the 17th with a magnitude 8.4 and fades to 8.9 by the end of the month. It is in the sky most of the night.

-- Brian Loader

9. Variable Star News

The latest Variable Stars South (VSS) Newsletter, 2017 No 4, October is now available from the website - https://www.variablestarssouth.org/ All newsletters can be found under the Tab Community; heading Newsletters and click on the particular newsletter image to download. The current newsletter has articles on some interesting stars: - Discussion of QZ Car, a quadruple system originally discovered at Auckland Observatory in the late 1960s. The published paper is Walker et al (2017) MNRAS 470.20074 - Consideration by Carl Knight of early ejection sequences of classical novae (the rising arm) with particular reference to Nova V5589 Sgr. - There is an analysis of the effect on observations of the 'one-day? orbital period phenomenon with V803 Cen, a pair of helium white dwarf stars.

As well as articles on a few other variables there is Part 3 of Mark Blackford's series on construction of his roll-off roof observatory at Congarinni, NSW, and its equipment.

-- Alan Baldwin

10. Solar Storms and Auckland's Damaged Fuel Pipeline

Physicists at Victoria University of Wellington and the University of Otago suggest geomagnetic storms can cause corrosion in New Zealand's pipelines, and some areas, including Northland, are more vulnerable.

Victoria's Dr Malcolm Ingham and Otago's Professor Craig Rodger are mid-way through a Government-funded research project that focuses on reducing the damage to electrical networks from currents induced in the ground by large geomagnetic storms. "When a solar eruption from the sun, for example, hits the Earth's magnetic field, it can cause rapid changes in the Earth's magnetic field'a magnetic storm," says Professor Rodger. "We're really vulnerable to these as we've become more and more technologically dependent. It can affect not only our power network, but also things like satellite communications."

However, Dr Ingham points out that because of the process of electromagnetic induction, currents induced in the Earth can also impact pipelines. "If there's a break in the pipeline's cladding, currents that travel from the pipe to the ground can cause corrosion of the pipe. To stop that happening, pipelines have power sources along them to keep the voltage of the pipe negative relative to the voltage of the ground. "However, more than 20 years ago, we carried out research that showed that the currents induced by geomagnetic activity cause the voltage of the ground to vary such that at times the pipe voltage becomes positive relative to the ground. This means that if you've got a hole in a pipeline cladding, variations in the geomagnetic field will cause corrosion over time, leading to containment failure and leakage."

New Zealand's geography controls the location and size of electrical currents in the ground, he adds. "Induced currents are typically larger in directions perpendicular to the coastline. Auckland and Northland are therefore especially vulnerable to such variations, because of the narrow make-up of the land."

Dr Ingham says last month's damaged fuel pipeline in Northland is probably an example of how pipelines can be affected by geomagnetic storms if the pipe cladding is damaged. "If a digger has previously, even years ago, scraped the coating of that pipeline, each geomagnetic storm since could have caused a little bit more corrosion and eventually it would give. That event also happened a few days after there was a big geomagnetic storm. To me, the effects of geomagnetic storms is something that should be considered when investigating the cause of the incident." More research needs to be done into how to mitigate corrosion to pipelines due to changes in the geomagnetic field, the researchers say.

Professor Rodger leads the Otago Space Weather research group and the Government-funded joint project into the potential damaging effects of "solar tsunamis" on the nation's electrical network. He says that pipeline corrosion is indeed another infrastructure impact that deserves careful investigation.

"While solar disturbances May create auroras beautiful to behold, the flip-side is that such awesome spectacles involve mind-numbingly amounts of energy suddenly flooding our geomagnetic field. Those changes could potentially play havoc with the technologies we are increasing reliant upon."

-- From Victoria University of Wellington Alumni News https://www.victoria.ac.nz/news/2017/10/solar-storms-and-aucklands-damaged-fuel-pipeline

Professor Rodger was after-dinner speaker at the RASNZ's Conference in Dunedin last May.

11. NZ's Stargazing Places Reviewed

It was as if a great celestial Bake Off was in action. Handfuls of sugar spilt across the sky and the faint floury stain of the Milky Way scattered overhead. With my neck craned all the way back, I felt dizzy trying to take in the immensity of it all. 'Here, the stars are so bright you can read the newspaper at night," laughs Hilde Hoven, one of the residents on New Zealand's Great Barrier Island.

In August of this year, Great Barrier - a 30-minute flight north-east of Auckland - was the first island in the world to be designated a Dark Sky Sanctuary. It's the third site in the world after the Cosmic Campground in the US state of New Mexico and the Gabriela Mistral Dark Sky Sanctuary, the site of Chile's government observatory.

This island of steep forested hills, wetlands and sweeping white-sand bays is completely off grid. All the residents are responsible for supplying their own power through solar, wind or gas. There are no billboards or street lights. And the complete lack of light pollution makes for a very sparkly stratosphere.

Typically, tourists come here to fish, hike and swap fast-paced city life for something slower. But come winter, visitor numbers drop from 12,000 to 2,500 and a solution was vital to support the island's 900 residents. It seems the starry solution was staring them right in the face and local residents Gendie and Richard Somerville-Ryan decided to apply for Dark Sky status.

Working with Auckland astronomer Nalayini Davies, they took readings all over the island one clear crisp night and sent the results off to the International Dark-Sky Association (IDA) for review. We thought we'd be a Reserve, but when the results came back they said, "You're not a Reserve" and we were really disappointed! They said, 'Your readings are technically darker than instruments should be able to measure - you have a very dark sky indeed!' grinned Gendie. 'What's strange is the darkest readings came on the west coast, closest to Auckland, which proves their light dome doesn't touch us. If it was too bright you wouldn't see Venus on the horizon.

Sanctuary rules are stricter than those of a Reserve because they have to be situated in a very remote location, promote long-term conservation and above all prove a night-sky brightness routinely equal to or darker than 21.5 mpsa (magnitudes per square arc second). Great Barrier Island has an mpsa of 21.97.

The effect has been immediate. After attending an intensive weekend training course - run by John Drummond, President of the Royal Astronomical Society of New Zealand - to become Dark Sky Ambassadors, Hilde (originally a translator) banded together with two other locals - Orla Cumisky (who works at the pub) and Deborah Kilgallon (a full-time mum) - to found Good Heavens and they now offer private stargazing experiences, starlit dinners with a gourmet chef and, on set dates, stargazing on the local beaches.

Hilde had their 8-inch Dobsonian telescope trained at the sky. 'OK, no peeking at your mobile phones - the white light destroys your night vision and it'll take 10 minutes for your eyes to adjust again,? she said, as we snuggled into beanbags positioned on the terrace of the hilltop Trillium Lodge. She beamed a green laser to point out the constellations of Sagittarius, Capricorn and Scorpio. 'In New Zealand, the scorpion's tail is known as Maui's Fishhook. Legend has it Maui [the Polynesian demigod] went fishing on his canoe one day and cast his hook into the ocean. As he hauled it in, many rocks appeared. He kept pulling and pulling until Aotearoa [New Zealand] appeared.

Next, the telescope was tilted towards Jupiter to see its moons, then Saturn to spy on its icy rings. But best of all were the constellations that are never visible in the northern hemisphere, such as the Southern Cross and the Magellanic Clouds - dwarf galaxies orbiting the Milky Way. And the new ways of seeing the familiar, such as Matariki - the Maori name for the Pleiades star cluster. Its appearance signals the start of the Maori New Year, but we know it as the Seven Sisters not far from Orion's feet.

I was eager for more, so flew down to South Island - home to Aoraki Mackenzie International Dark Sky Reserve, established in 2012. One of eight reserves in the world, it includes the Mount John Observatory where travellers can use the most-powerful telescopes in the country to peer into deep space. But I wanted something more intimate.

Luke and Kaye Paardekooper run Mount Cook Lakeside Retreat on the shores of Lake Pukaki inside the reserve. Having hosted the likes of Oprah Winfrey, film director James Cameron and NASA planet-hunter Natalie Batalha, they're well set up to offer luxury. Their private villa has uninterrupted views of the lake and an outdoor hot tub bubbling away at all times.

'Choose any bottle you like from the wine cellar, and then after dinner [a three-course affair prepared by chef Luke Mathewson] we'll head over to the observatory for a spot of stargazing,' said Luke. Sadly, halfway through dinner, dark clouds rolled in, obscuring the skies.

'It's best to visit in winter when the angles of the Earth allow you to see the full spread of the Milky Way - plus you don't have to stay up too late for it to get dark,' said Kaye, who is on the local Dark Sky board. 'Otherwise, time it for when the moon is new; visit when it's full and the dark sky will be outshone.'

Tucking in to dessert, I asked the awkward question: 'Will there be competition with Great Barrier Island now?' She shook her head. 'No, the more people talking about dark skies the better - it's not all about tourism, it just as much about conservation.'

One place taking conservation seriously is Skyscape, a new stargazing glasshouse that's just won a Qualmark Environmental Gold Award (handed out to just nine per cent of New Zealand properties). Lying in the southwest corner of the reserve, this solar-powered, one-room hideaway is tucked, hobbit-style, into the hillside. Its grass roof makes it impossible to pick out amid the tussock-laden landscape.

The brainchild of Bevan and Bridget Newland, Skyscape is set within the 6,000-acre Omahau Hill merino sheep station. Farm tours are offered, but mostly you're left in seclusion to soak up the snow-capped Two Thumb and Ben Ohau ranges rolled out before you. Days are spent sipping fine wine, spotting Marcus, the local highland bull, watching Australasian hawks hunting rabbits and paradise ducks that 'sound like fighter jets when they're landing,' according to Bevan. There's not another building in sight. Come nightfall, you can roll back the retractable sun blind, pull out the star chart and binoculars, and set to finding celestial bodies.

'There is Wi-Fi, but we tell people to turn it off. Skyscape is about totally switching off,' says Bevan. With a reported 99 per cent of Americans and Europeans no longer able to see the Milky Way due to light pollution, it's time to head south. Move over Hollywood, there's a new star in town.

-- See Emma Thomson's complete article at http://www.telegraph.co.uk/travel/destinations/oceania/new-zealand/articles/stargazing-in-new-zealand/ Thanks to John Hearnshaw for passing on the link.

12. Surprising Science from Cassini's Grand Finale

You'd think scientists would have Saturn all figured out after watching it up close for 13 years. They don't.

When NASA's Cassini spacecraft eased into orbit around Saturn in July 2004, its "to-do" list spanned every aspect of the Saturn system. Yet some of the mission's most memorable moments were close encounters with the planet's vast system of moons - from a single brush with two-faced Iapetus to 127 close flybys of huge, murky Titan (which included delivering the European Space Agency's Huygens lander).

But during the spacecraft's last four months in residence, the scientific focus was almost exclusively on Saturn itself and the majestic, dramatic, complex ring system that surrounds it. This "grand finale" carried Cassini on 20 orbits that skimmed just outside the main ring system and 22 that threaded a corridor between the planet and the vestiges of its innermost ring.

During a meeting of the American Astronomical Society's Division for Planetary Sciences, held in mid-October in Provo, Utah, a parade of Cassini scientists offered some of the insights they gained during this unprecedented scrutiny.

The final orbits sent the spacecraft dashing at 35 km/s north to south through a planet-ring gap about 2,400 km wide between the planet and the rings. But this region isn't truly empty - Cassini got a chance to directly sample the hydrogen and other compounds present in Saturn's uppermost atmosphere.

It's those "other compounds" that have planetary scientists scrambling for explanations. In theory, material is leaking from the innermost threads of the ring and drifting toward the planet, and generally the rings consist almost entirely of water ice. But investigator Mark Perry (Johns Hopkins University's Applied Physics Laboratory) reports that Cassini's Ion and Neutral Mass Spectrometer (INMS) found surprisingly little water in the planet-ring gap. That's partly due to water's tendency to stick to the tubing inside the INMS, Perry explains.

Instead, the mass spectrometer swept up many heavier compounds that haven't yet been identified. For example, a peak with an atomic weight of 16 is most likely methane (CH4), a gas that shouldn't be percolating up from the atmosphere and would be chemically out of place in the water-ice rings. Another peak at 28 could be carbon monoxide (CO) or molecular fragments of carbon-bearing dust particles. Confirming either of these will take more modelling to explain.

The close passes also allowed dynamicists to use tiny changes in Cassini's velocity to probe the planet's gravity field. As Michele Dougherty (Imperial College London) noted, this analysis is just getting started - but already it's raising questions about the state of Saturn's deep interior. One key question is whether the core is a distinct rocky mass or something more like the "fuzzy" dispersed core that Jupiter seems to have.

Meanwhile, Dougherty reports, Cassini got its best-ever chance to measure Saturn's magnetism. Earlier results had shown that the magnetic field was aligned closely with Saturn's spin axis, a unique arrangement in the solar system. But the close-in measurements now show that the axial alignment is incredibly close - to within about 0.06°. Saturn's magnetic dynamo likely occurs in a layer of metallic hydrogen deep inside the planet, but dynamo theory requires a tilt to generate a magnetic field.

"It's almost as if you can use the magnetic field to see inside Saturn itself," she notes, adding that the situation "must be more involved than we thought." She expects more clarity to emerge in a few months, after data from all the Grand Finale orbits have been analysed.

Cassini's close-in flybys also gave mission scientists a chance to examine the rings in extreme detail. They'd gotten one other opportunity like this - when the spacecraft passed very close to the planet during its arrival in 2004. But the final orbits provided a chance to re-examine some curiosities more intensively.

Matthew Tiscareno (SETI Institute) delved into three of these at the meeting. He described new views of clumpy structure in the main rings (dubbed "straw") that Cassini had seen earlier. Tiscareno can't yet explain how or why this occurs - the higher-quality images show that the clumpiness doesn't correlate with the pattern of rings or with sets of gravitationally induced waves found in them.

Other ring oddities, known as "propellers," are local disturbances in the myriad particles created by embedded but unseen bodies that range in size from 100 meters to 1 km across. Swarms of these features cluster in A ring - many small ones lie in the middle of the A ring, while the largest are found in the outer A ring. Tiscareno explained that some propellers have been tracked throughout Cassini's mission, and the final images should allow him and others to deduce not only the embedded moons' masses but also the sizes and distribution of ring particles sweeping by them.

Meanwhile, the ring system presents a huge yet delicate target for chunks of interplanetary debris up to a few meters across. When these strike the rings they create brief clouds of disrupted particles, and new images show lots of these splats. Tiscareno reports that colour information in the Cassini images should give mission scientists a handle on the composition of the colliding objects.

As with any good space mission, Cassini has raised some important new questions. For example, because of the near-identical alignment of Saturn's magnetic and rotation axes, scientists have struggled to determine just how fast the planet spins. We can see the motions of its clouds, but the rotation rate of its deep interior is still uncertain.

Another question is whether Cassini's Grand Finale observations can pin down the total mass of Saturn's rings - critical to models of how and when they formed. Project scientist Linda Spilker (Jet Propulsion Laboratory) hinted that, based on the analysis so far, that mass might be less than expected. But, as with all of these preliminary results, the final answer is still months away.

-- See Kelly Beatty's original article with images and links at http://www.skyandtelescope.com/astronomy-news/surprising-science-from-cassinis-grand-finale/

13. How to Join the RASNZ

RASNZ membership is open to all individuals with an interest in astronomy in New Zealand. Information about the society and its objects can be found at http://rasnz.org.nz/rasnz/membership-benefits A membership form can be either obtained from This email address is being protected from spambots. You need JavaScript enabled to view it. or by completing the online application form found at http://rasnz.org.nz/rasnz/membership-application Basic membership for the 2017 year starts at $40 for an ordinary member, which includes an electronic subscription to our journal 'Southern Stars'.

14. Email Address Changes, Please

Anyone with these email addresses will need to advise us of a new one: clear.net.nz es.co.nz ihug.co.nz paradise.net.nz pcconnect.co.nz quik.co.nz vodafone.co.nz wave.co.nz

Please send address changes to <This email address is being protected from spambots. You need JavaScript enabled to view it.> . Thanks to those who have already done so.

15. Next Newsletter December 16

The December Newsletter will be circulated on or before December 16th.


"I have yet to see any problem, however complicated, which, when looked at in the right way did not become still more complicated." -- Poul Anderson.

"Good judgement comes from experience, and often experience comes from bad judgement." -- Rita May Brown.

Newsletter editor:

Alan Gilmore Phone: 03 680 6817
P.O. Box 57 Email: This email address is being protected from spambots. You need JavaScript enabled to view it.
Lake Tekapo 7945
New Zealand