Reflections - April 2014
March 28, 2014 | By administrator |
Journal of the Northern Sydney Astronomical Society Inc. General Meetings: Ination Confrmed I I The Brihat Samrat Yantra has other uses. From page 4
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Calendar General Meetings: NAG Meetings: Observing Nights: Solar Observing: Deadline: June 21st Speaker: TBA July 19th Speaker: TBA August 16th Speaker: TBA Fourth Tuesday of the month Consult NSAS’ web site at http://nsas.org.au/observing/ First
General Meetings: February 16 th Speaker: Professor Charlie Lineweaver - Habitable planets and the Gaia theory March 15 th Speaker: TBA NAG Meetings: In Recess. To resume later in the year Observing Nights: Consult NSAS’ web site at http://nsas.org.
General Meetings: October 20 th Annual General Meeting November 17 th Speaker: Jan Hamaan - CERN December 13 th Christmas BBQ NAG Meetings: To resume 2016 Observing Nights: Consult NSAS’ web site at http://nsas.org.au/observing/ Deadline: Please
General Meetings: May 19 th Speaker: Bob Fuller - Sky stories of the Dreaming June 16 th Speaker: Kyler Kuehn (AAO) - Star Bugs: Observing the heavens with a hundred eyes July 21 st Speaker: Angel Lopez-Sanchez (AAO)- Astronomy and Light July 21 st
General Meetings: February 17 th Speaker: Dr. Irakus Konstantopoulis (AAO) March 17 th Speaker: Dr Kyler Kuehn (AAO) NAG Meetings: In recess Observing Nights: Consult NSAS’ web site at http://nsas.org.au/observing/ Deadline: Please send your contributions to the April 2015 issue of Reections in time to reach the editor before March 15 th to email@example.com Calendar W hen you think of Lightning Ridge you’d normally think of Opals, and indeed if the famous Black Opal hadn’t been discovered at this location, I would guess that there would be little likelihood of a town springing up in this isolated, pebbly region. My husband, Graham, and I answered a call for scopes from Bob Fuller to NSAS members for a star party at the Ridge on Saturday, 22 November 2014. His invitation pointed out that at that time of the year it would be very hot, and the trip would take about nine hours. Graham and I were the only ones from NSAS who took on these challenges and we can say that Bob was correct on both counts. Yes, it was hot; very hot. And yes, it was a long way. It’s interesting how a nine-hour trip feels much longer as you get older! We went the shortest route from home, via Bells Line of Road, Lithgow, Mudgee, Gulgong, Gilgandra, Walgett to Lightning Ridge. We decided to break the trip both ways. On the way up we stayed at Gulgong, and on the way back at Mudgee. Once we arrived at the Ridge we loved the place. On the Saturday morning I did a tour of the ‘Walk in Mine’ (it was absolute heaven to escape the 44 degree heat) and of course visited several opal vendors (I was tempted, but in the end I didn’t buy). We also stopped by a very intriguing structure called the ‘Astronomers Monument’. It was built by a local, Alex Szperlak, to commemorate the great astronomers including Copernicus, Isaac Newton, Galileo, Kepler and E. Halley. The monument was built (apparently) from left-over concrete, using different sized buckets to give it a unique shape. From what we heard from the locals, no telescope was ever set up on the site. To me, it’s just a very, very odd building. On the Saturday afternoon we attended, at Bob’s invitation, a “Giving Back” ceremony. For the last couple of years Bob has been undertaking a research project into the sky knowledge of the Kamilaroi and Euahlayi peoples. This afternoon Elders were invited to receive material prepared as part of this project. The audience was also treated to a very enlightening video made as part of the overall project and premiered at Lightning Ridge, called “Sky Stories of the Dreaming”, all about aboriginal astronomy. A Macquarie University media release of 5 December 2014 1 highlighted three new areas of knowledge which came from this project: The use of patterns of stars in the sky 1) as “waypoints” for teaching travel to ceremonies; The close connection between 2) songlines 2 in the sky, songlines and Dreaming tracks on the ground, trad- ing routes, and star maps, and The knowledge concerning the back- 3) ground to the cultural belief of “what’s up there is (or was) down here”. A cultural performance of dancing and singing concluded the ceremony. In the evening there was the star party. I’d forgotten what clear skies looked like, it was a phenomenal sight. About 50 people came along, many indigenous who came to see the stars and link them with the stories they knew. For many this was the rst time they’d looked at the sky through a telescope. The Large Magellanic Cloud (LMC) could be seen clearly with the naked eye in the SE sky. In aboriginal lore the LMC is the campsite of an old man, whereas the Small Magellanic Cloud (SMC) is the campsite of his wife. The couple, known jointly as Jukara, had grown too old to feed themselves, so other star beings bring them sh from the sky river we know as the Milky Way. 3 Pleiades, a star cluster known as the Seven Sisters, also raised a lot of interest. In dreamtime stories they were seven beautiful ice-maidens. Two were captured by a man called Wurrunnah while their ve sisters travelled to their home in the sky. A Star Party at Lightning Ridge Lightning Ridge is well-known for its Black Opals which are mined underground. Outside the “Walk in Mine”, a mine open to tourists, is the “Big Hoist”. Built between 1985-1988 it was one of the biggest hoists in Lightning Ridge at that time. It was able to carry a large quantity of dirt, which reduced the amount of labour and effort required in moving dirt to the surface and trucking it out. The strangely shaped Astronomers’ Monument
General Meetings: October 21 st Annual General Meeting November 18 h Speaker: Dr Andrew Sheinis (AAO) - The development of astronomical instrumentation. December 16 th Christmas Party NAG Meetings: Every fourth Tuesday of the month Observing Nights: Consult NSAS’ web site at http://nsas.org.au/observing/ Deadline: Please send your contributions to the January 2015 issue of Reections in time to reach the editor before December 15 th to firstname.lastname@example.org Calendar A few Meteorites are from Mars O f over 61,000 meteorites found on Earth, a mere 132 have been identied as Martian in origin . This article outlines the detective story of how that identication was achieved. Stony meteorites account for some 94% of all meteorites found on Earth. Of these, over 90% are chondrites, so called because almost all are composed of small spherical particles (chondrules) that appear to have melted while freely oating in space prior to their incorporation in meteorites. Chondrites are typically about 4.55 billion years old (based on radiometric dating) and are thought to represent material from the asteroid belt. 4.55 billion years has been taken to represent the age of the Solar System and the time of formation of asteroids. The other kind of stony meteorite, achondrites, is thought to have crystallised from a magma in the same way as terrestrial rocks. Among achondrites, a small number of igneous meteorites were identied by the 1980s as being anomalously young and having oxygen isotope compositions that differed from those of other meteorite groups. These anomalous meteorites were collectively called SNC meteorites. This name was based on the meteorites’ classication into 3 types, each named after a type specimen: Shergottites, named after the • Shergotty meteorite that landed in the Indian village of Shergotty in 1865 (96) Nakhlites, named after the shower • of meteorite stones that landed in the Egyptian village of El Nakhla el Baharia in 1911 (13) Chassignites, named after the • shower of meteorite stones that fell on the French village of Chassigny in 1815 (2) [The number of meteorites in each sub-group as at 9 January 2013 is shown in brackets; 3 of the total of 114 SNCs are unclassied.] The nakhlites and chassignites have ages, based on radiometric dating, of around 1,300 Ma. Shergottites are even younger at about 165-200 Ma. As igneous rocks are generally formed by crystallisation of molten rock as it cools, the straight-forward explanation for these young ages is that they represent when the SNC rocks crystallised from a melt. But this rules out SNCs having a source in the asteroid belt since the necessary igneous activity would have occurred long after it had been assumed that the asteroids had cooled and solidied. Suggestions that SNCs might have come from a planetary body like Mars initially faced the objection that no meteorites from the Moon had been discovered and an impact capable of ejecting a fragment of the lunar surface into an Earth-intersecting orbit was surely much more probable than such an event on Mars, given the Moon’s lower escape velocity and close proximity to the Earth. This objection fell away, however, with the unanimous acceptance that meteorite ALH A81005, found in the Allan Hills region of Antarctica in 1982, was of lunar origin. Consensus was readily achieved because ALH A81005 was identical in mineralogy, mineral chemistry and isotopic composition to Apollo and Luna  samples brought back from the Moon to Earth. The conventional view that the dynamics of cratering of planetary surfaces by asteroid impact was unfavourable to producing meteorites was thus overturned. Since the crystallisation ages of SNCs lie between 165 and 1,300 Ma, SNCs have to originate from an astronomical body that featured molten rocks as recently as 165 Ma ago. The giant planets can therefore be eliminated because their exterior layers are predominantly gas and/or ice, not rock. The absence of blocks of ejecta when the comet Shoemaker-Levy/9 hit Jupiter reinforces this conclusion. Comets and Kuiper Belt objects can be eliminated because they have never been molten. Thus, the source for SNCs narrows EETA 79001 aka Elephant Moraine 79001 as found in Antartica Picture Credit: NASA EETA 79001 Picture Credit: NASA
In this issue Page 1: Editorial President’s message Page 2: Calendar/Communications Dr. Brian Schmidt @ NSAS Cryogenics Page 3: NSAS Field Trip Page 4: Spotlight on... Page 5: What makes Venus so bright?