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DISPLAYING POSTS TAGGED: astronomy (18)

Rings around an asteroid

Author
by Tanya
Publish date
31 March 2014
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In a surprise discovery, two rings have been found around the asteroid Chariklo, making it the first small Solar System body known to have rings.

Saturn is known for its magnificent rings and the other gas giants - Jupiter, Uranus and Neptune - have ring systems too, though not quite as impressive. Careful searches had not found any other ring systems within the Solar System and many astronomers were beginning to think that rings might only exist around large objects, until now.

Rings from Chariklo An artist's impression of the newly discovered rings around Chariklo.
Source: ESO/L. Calçada/Nick Risinger (skysurvey.org)
 

Chariklo is just 250km across and lies beyond Saturn, at a billion kilometres away. It is much too small and far away for the rings themselves to be seen, but amazing detail is now known about them. The rings are dense but narrow, just three and seven kilometres wide, and are separated by a clear gap of nine kilometres. If you were standing on the surface of Chariklo, the rings would appear as wide as our Full Moon and stretch from horizon to horizon.

The discovery was made possible because last June, Chariklo passed in front of an obscure star (UCAC4 248-108672). Not only did Chariklo block the star's light for 5 seconds, but two tiny dips in the starlight were seen, just before and after Chariklo moved by. This video from the European Southern Observatory (ESO) shows faint dimming caused by the rings, just before and after Chariklo blocks the star completely.

 

This event, known as an occultation, could only be seen from South America and an observing campaign was coordinated across seven observatories, including two telescopes operated by the ESO at La Silla, Chile. Having observations from all seven observatories, ruled out other possible explanations, except for a ring system.

What I really love is the data from the new high-resolution camera on ESO's 1.54m Danish telescope. (Anyone who has been to my Discover the Night Sky series knows that I am particularly fond of beautiful graphs!) This new camera was developed to search for exoplanets and can take up to 40 images per second. It was actually able to see the gap between the two rings – now that's beautiful science!

Chariklo Data The data captured by ESO's 1.54m Danish telescope, showing Chariklo blocking out the light of the star (the main dip). On either side are two small, double dips, as the rings also passed in front of the star.
Image: F. Braga-Ribas et al.
Source: Reprinted by permission from Macmillan Publishers Ltd: Nature (March, 2014)
 

The Planetarium's astronomer, Dr Tanya Hill, was recently appointed the Australian representative of the European Southern Observatory's Science Outreach Network.

Links:

Great Melbourne Telescope volunteers

Author
by Kate C
Publish date
13 March 2014
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Each Wednesday, a dozen or so engineering and astronomy buffs head to a museum workshop to restore one of Marvellous Melbourne's grandest marvels. The Great Melbourne Telescope (GMT), scorched by the Mount Stromlo fires in 2003, is being resurrected thanks to an estimated 10,000 hours of volunteer work (so far). This group recently received a Certificate of Appreciation in the 2013 Arts Portfolio Leadership Awards.

GMT restoration team Mathew Churchward reading out the Arts Portfolio Award commendation to the Wednesday restoration workshop team.
Source: Museum Victoria
 

The workdays have "a bit of a men's shed feel about them," says Senior Curator Matthew Churchward. He coordinates the project alongside Curator of Engineering Matilda Vaughan. The combined knowledge in the room – all members of the Astronomical Society of Victoria, many with experience in engineering, electronics, astronomy and optics – means this piece of 19th-century technology is in expert hands.

Three men with computer L-R: Barry Cleland, John Cavedon, new volunteer Norm and Stephen Bentley working on technical drawings of GMT parts.
Source: Museum Victoria

Building telescopes is a common pastime for amateur astronomers; volunteer Barry Adcock has a home-built a 14-inch diameter telescope for his backyard dome observatory, plus another telescope that allows him to view the stars from inside his house. For many, stargazing is a habit they picked up when very young. Scottish-born Jim Pollock recalls a lunar eclipse in 1949 during which the moon was bright blue after forest fires in Canada. "In the atmosphere, tiny particles of pinene, the oil from the pine trees, scattered red light beautifully and just let the blue light through." Another volunteer, Barry Clelland, remembers looking up as a kid from his backyard in the suburbs and thinking, "that's half the universe there. You could see the Milky Way in Heidelberg back then."

On this day, a sub-group is working on the mirror polishing and grinding machine, a beautiful hulking contraption with a cast iron frame and gears and shafts. The GMT's half-ton speculum metal mirrors tarnished over time, so every few years they were removed and reconditioned with this machine. "We're still trying to work out exactly how it was driven," says Matthew. The mirror sits on a rotating table and as it moves, the polishing head also rotates, "so it doesn't get a flat spot in any part of the mirror. It keeps moving as it's rubbing." Or, like "patting your head and rubbing your tummy," jokes volunteer David Linke. The team hopes to have the polishing machine working within the next year as a hint of what's to come with the telescope itself.

David Linke with the mirror polishing machine. David Linke with the mirror polishing machine.
Source: Musuem Victoria
 

In the workshop, parts of GMT are laid out on pallets and benches. With a grin, David says, "it's a big jigsaw puzzle, isn't it?" Above it all, for equal parts reference and reverence, hangs a large-scale historical picture of the GMT in operation.

Museum workshop A view of the workshop with the GMT’s lattice tube in the foreground. On the back wall hangs the large historical photograph of the GMT at the Melbourne Observatory.
Source: Museum Victoria
 

Most of the large parts of the GMT were recovered after the 2003 Mt Stromlo fires. "Oh golly, it was a dirty job to get everything out of that cube," recounts David. "The aluminium had melted from the dome and filled up the screw holes so you couldn't see where things were undone." Many months of work saw the GMT dismantled and its surviving parts audited. Fortunately, the GMT had an unofficial champion in Barry Clark, who has been involved with the Melbourne Observatory since 1955. At that time, decommissioned equipment went into storage and was at risk of being lost. Says Matthew, "Barry's been instrumental in recovering bits and pieces that were hidden under the floor. He's discovered some key bits of equipment that went right back to the very earliest observatory at Williamstown."

Detail of the dismantled cube of the GMT. Detail of the dismantled cube of the GMT.
Source: Museum Victoria
 

Lengthy reverse-engineering is recreating the missing parts. "We go out there with a ruler and pencil and paper, take measurements and sketch it up roughly," says Campbell Johns. The measurements are made in imperial units to match Irish manufacturer Thomas Grubb's original specifications, before conversion to metric for fabrication. Some of the team with technical drawing expertise convert the workshop sketches into digital CAD files. There's a lot of cross-checking with old photographs, drawings and the extant parts.

"We don't even know if there was ever a full set of working drawings," says Matthew. "It appears they did the basic layout and started building it before they had the detailed design. You can see evidence in the way parts were modified during the construction process, like spots flattened out of a casting to make a seat for another component." A volunteer adds, "Pretty amazing given in those days there were no angle grinders or power drills or oxy welders. It was all done with cold chisels."

Three men with computers L-R: Barry Clark, Barry Adcock and Mal Poulton working on optics design specifications for the GMT.
Source: Museum Victoria

So why are these men devoting their spare time to this project? It's evident from the way they talk about the GMT that they admire its history and innovation. In addition to its astronomical achievements, including the first observations of southern nebulae, the ingenious nature of its design bewitches them. It had two axes and counterweights that allowed just one person to move the beautifully balanced telescope. In its lifetime there were larger scopes, but none so nimble. Matthew's view is that it's an opportunity of a lifetime for amateur enthusiasts to build such a large telescope; few individuals would have the resources to do so alone. Other volunteers nominate restoring an important part of Melbourne's history as their prime incentive – they want to see it back in its old home.

Indeed, the end goal is to return the working telescope to the Melbourne Observatory for public viewings. Its original configuration restored, there may be new electronic additions to allow digital photography or remote operation via the web. As Matthew says "It could be very inspiring for astronomy in Victoria."

Links:

The Great Melbourne Telescope website contains the story of the telescope, and updates about its restoration through the ASV's Phoenix newsletter

Follow the GMT project on twitter: @GMT21stC

Great Melbourne Telescope on Collections Online

The problem with Pluto

Author
by Tanya
Publish date
18 February 2013
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On 18 February 1930, Clyde Tombaugh achieved an amazing feat - he discovered Pluto. It’s said that he was a meticulous astronomer and I’m sure he must have needed all that mettle to have stumbled upon the tiny speck that was Pluto.

Over six years ago, Pluto grabbed headlines when astronomers famously ‘demoted’ the planet and designated it as the first of the dwarf planets. Some were disappointed by this – but I have to say that Pluto has always been a bit of an odd-ball. It was something we had explored a year earlier with the release of our planetarium show, The Problem with Pluto, in 2005.

The Problem With Pluto In this planetarium show, Lucy is on a research craft with her mother Lillian, a scientist, and together they are gathering data to discover just what Pluto’s status should be.
Image: Melbourne Planetarium
Source: Museum Victoria
 

A fellow astronomer shared with me his interesting way to explain it. Imagine, as a child, having a case full of pencils. The pencils came in all different colours but at their heart they were the same; except for one. It was a bit odd, still good for colouring-in just like a pencil, but there was something different about it. Nonetheless, it was the only one you’d even seen and it had always been in the pencil case, so you called it a pencil along with all the others. Then, one day at a friend’s house, you opened their pencil case and it was filled with something called crayons. Your eyes lit up with recognition. That odd-ball pencil you’d been worried about wasn’t odd after all, it was in fact a crayon.

When Pluto was discovered, it was one of a kind at the edge of the Solar System. It wasn’t a terrestrial planet, it wasn’t a gas giant, but it did orbit the Sun. Seventy years on, we now know of thousands of objects orbiting alongside Pluto. They are the icy worlds that make up the Kuiper Belt. Pluto, because it is big enough to be round, is still a bit special and so it now goes by the new label of dwarf planet.

On Pluto Day, I’ll be celebrating that Pluto has now found its rightful place in the Solar System.

New Horizons spacecraft Right now, a real research craft is on its way to Pluto. Called New Horizons it will fly by Pluto in July 2015 and journey on to discover more about the Kuiper Belt.
Source: NASA
                       

Links

The Problem with Pluto will be showing at the Melbourne Planetarium at 2pm, 18 February to 4 March.

Siding Spring Observatory

Author
by Tanya
Publish date
14 January 2013
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Like other Australian astronomers last night, I was glued to the computer watching as a fire raged across the Warrumbungle National Park in NSW, home to Australia's world-class optical and infrared telescopes at Sliding Spring Observatory. I think the hardest thing was knowing that it's almost 10 years ago to the day, that fires destroyed the Mt Stromlo Observatory in Canberra. Could this really be happening again?

Fire around telescope A truly frightening image, as Australia's largest optical telescope, the Australian Astronomical Telescope (AAT), is engulfed in smoke.
Source: Rural Fire Services
 

Fires around telescope Fires blaze around cottages in front of the AAT. To the top right of the image are the flames that engulfed the lodge.
Source: FTS webcam
 

Fire at astronomer's lodge The glow as the astronomer's lodge is destroyed. Temperatures at the AAT were measured to be over 100 degrees.
Source: FTS webcam
 

Thankfully, lessons were learnt from that event and there is much hope that measures put into place may have saved the dozen or so telescopes on the mountain. We'll have to wait and see as the damage is assessed over the next few days.

The good news is that all 18 staff were evacuated safely. Many telescope domes are still standing, as new images come through this morning. The building which has been destroyed was the lodge which provided accommodation for astronomers during their observing runs. 

Fire around telescope Electronics were not meant to survive such temperatures.
Source: HATSouth webcam
 

Telescope dome after fire The picture I wanted to see today. The AAT dome still stands, but there will be a wait to access how the telescope fared inside.
Source: LCOGT webcam
 

Our thoughts are with the community of Coonabarabran and those who have been affected by the fires, and our thanks go out to fire services for their great efforts. 

If the telescopes had been destroyed it would have been devastating for Australian astronomical research, all but ending our ability to do continue doing optical astronomy here. Hundreds of researchers and students rely on those telescopes. And it would also have affected the Coonabarabran community, many of whom rely on the telescopes for their livelihoods too.

Images of the event, many taken from the webcams that are normally used by astronomers to check sky conditions during their nightly observations, tell the story.

burnt astronomer's lodge building The burnt out remains of the astronomers lodge. I have fond memories of Margaret's delicious chocolate pudding, which I would devour there, before heading up to the telescope for the night's observing run!
Source: Rural Fire Services

Telescope dome after fire The square "dome" on the left houses the ANU's 2.3 metre telescope which stayed a comfortable 20 degrees throughout the fire. The dome to the top right is the new SkyMapper telescope, led by Nobel Laureate Brian Schmidt and built to continue the work of the Great Melbourne Telescope after it was destroyed in the Mt Stromlo fires. Temperatures there peaked at 65 °C.
Source: Rural Fire Services
 

UPDATE: 

The Warrumbungle Shire Council has set up a Warrumbungle Shire Mayor’s Bushfire Appeal with donations being used solely to assist residents affected by the fire. The NSW Rural Fire Service are reporting that some 40 properties and over 110 out-buildings have been confirmed lost as well as a large number of livestock and farm machinery.

 

Links:

Siding Spring after the fires of January 2013 via Observations Blog, Sydney Observatory

Report from The Australian

Astropixie liveblogging the fire: Sunday night and Monday morning

Casting for the Great Melbourne Telescope

Author
by Matilda Vaughan
Publish date
21 December 2012
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Matilda swapped a life working as an engineer for a life curating the museum’s historical Engineering collection. She’s very curious about how stuff works, how it’s made and why. If a machine’s got a switch, she’ll definitely flick it.

Last week I visited a foundry in Melbourne that was casting a vital component for our restoration of the Great Melbourne Telescope. The original part of the telescope - the declination disc - had been modified and broken at some time in its history and was not repairable.

Great Melbourne Telescope in 1870 The Great Melbourne Telescope in its own house at the Melbourne Observatory, 1870. The red arrow points to the declination disc needing replacement.
Source: Museum Victoria
 

This is the first part of the project to be made by a sand moulding or casting process very similar to that which was used in Ireland in the late 1860s. Our modern part is made from a type of cast iron invented in the 1940s which has magnesium added to give it properties that make it easier to shape. The electric induction furnace, which is used to melt the metal, was developed in the early 20th century.

A couple of weeks ago, Peter made a pattern out of wood for the casting. Tom next used the pattern to form a hollow in a sand mould. This kind of mould is a mixture of washed sand and a binder, made in two halves, and cured to retain its shape once the pattern is removed. The two halves of the mould were then closed, after a pouring spout, flow paths and risers (to allow the metal to flow to and fill all sections of the hollow) were added. Heavy weights on top ensured it remained closed when the metal was poured.

Man working with metal The sparks fly as Bryn takes a sample from the furnace for temperature testing.
Image: Matilda Vaughan
Source: Museum Victoria
 

The pounded earth floor and the filtered light through the open doorways and skylights in the roof of the foundry transported me back in time. It was 7 AM and Bryn had already been awake for hours and the sparking pot of molten metal (spheroidal graphite iron) was his morning's labour. He tested its temperature and composition, turned the knob of the electric induction furnace's control panel, and gave the signal. After the removal of the slag crust, the metal was ready for pouring.

Man pouring molten metal Bryn pours the molten metal into the next mould as Tom looks on. Our filled mould is on the floor behind them.
Image: Matilda Vaughan
Source: Museum Victoria
 

Bryn added the final ingredients and carefully tipped the 1500°C molten metal into the pre-heated ladle. He then transported the ladle to the moulding area and poured it first into our waiting mould, and then onto the other smaller moulds. Being such a large casting, ours needed almost 24 hours to cool down before breaking open the mould.

Sand mould in workshop The lower half of the sand mould, with the casting removed. The sand from the top half is in pieces in the background. The sand will be cleaned and reused, as will the molten scraps of metal.
Image: Matilda Vaughan
Source: Museum Victoria
 

At 6 AM the following morning, Bryn was ready to break open the mould. The weights were removed and the upper part of the mould lifted away. Then the casting itself was lifted into the air and the sand and metal debris removed. It was then transported by the overhead mobile crane to the finishing room, where the hardened parts of the spout, risers and flow paths were ground and knocked off and the surfaces cleaned.

Men with newly cast metal pieces Bryn (left) with the pattern for our declination disc, and Tom (right) with the freshly removed casting. Note the four cylindrical 'risers' at the edge, the pouring pathways (almost like a running person) in the middle and the square shaped pouring spout (head of the running person). These pieces are reused for the next batch of metal.
Image: Matilda Vaughan
Source: Museum Victoria
 

The next step for this part will be heat treatment to 'relax' the metal, followed by the final shaping and machining. It is a rare sight to see this process so close in our urban environment and one of the great aspects to working on restoration projects of this magnitude.

Links:

Great Melbourne Telescope website

Great Melbourne Telescope on Collections Online

Watching the total solar eclipse

Author
by Tanya
Publish date
14 November 2012
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I had never seen a total solar eclipse before, and I was very excited to travel to Queensland to watch Australia's first solar eclipse in a decade just before 6AM this morning. 

It was incredible to wander down to the beach at 4AM and see it already packed with eclipse chasers! Thousands of people were at Palm Cove alone, more in surrounding Cairns and Port Douglas, while some headed inland where the weather prospects were better.

People on beach Eclipse chasers on the beach at Palm Cove, Queensland, awaiting the total solar eclipse.
Image: Tanya Hill
Source: Tanya Hill
 

We saw a magnificent sunrise over the water, but minutes later, when the partial eclipse was due to begin, the Sun disappeared behind clouds. It was an anxious wait but half an hour later, the clouds parted and we all donned our eclipse glasses to see a large chunk missing from the Sun.

The totality was perfect. Just beforehand you could tell that the surrounding light was different; it seemed sharp and unnatural. Then the brilliant diamond ring effect lit up the bottom of the sun and the moment had begun.

Total solar eclipse The moment of perfect totality, when the Moon was exactly in front of the Sun.
Image: Tanya Hill
Source: Tanya Hill
 

I was amazed by the colour - we could really see the pink prominences dancing around the Sun. Everyone cheered and just enjoyed the beauty of this natural show. We could see Venus shining bright above the Sun, the wispy corona and the Sun's outer gaseous layer, along with a dazzling bright ring encircling the Moon. It was surprising how long the two minutes lasted. The second diamond ring effect was blinding and spectacular as the Sun began to emerge once again.

The Yolngu of Arnhem Land tell their eclipse story of the sun-woman and moon-man coming together in the sky as husband and wife. It struck me that this is a phenomena that has been seen by so many, across thousands of years. I feel so fortunate to have shared in the experience.

Links:

'Eclipse groupies take shot in the dark,' The Age, 11 November 2012

'Eclipse sheds light on sizzling sun,' The Age, 14 November 2012 

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Updates on what's happening at Melbourne Museum, the Immigration Museum, Scienceworks, the Royal Exhibition Building, and beyond.

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