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DISPLAYING POSTS TAGGED: astronomy (20)

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 

November solar eclipse

Author
by Tanya
Publish date
1 November 2012
Comments
Comments (5)

Coming up on the 14th November we have the chance to see a solar eclipse. From here in Melbourne it will be a partial eclipse, with 52 per cent of the Sun's diameter covered by the Moon. But up in Far North Queensland and the topmost of the Northern Territory, they will be treated to totality, where the Moon will completely block the Sun for just on two minutes.

Partial Solar Eclipse A partial eclipse will be seen from Melbourne on the 14 November 2012.
Source: Museum Victoria
 

The eclipse will occur during the early morning of 14 November, with the Sun still low in the east. Therefore, a good view of the horizon will be needed. The timing for Melbourne is as follows:

Eclipse begins: 7:16am
Mid-eclipse: 8:06am
Eclipse ends: 9:00am

It is important never to look directly at the Sun, even during an eclipse. While the Sun may appear less bright it can still cause long lasting eye damage.

There are safe ways to look at the eclipse – at the Scienceworks shop you can purchase eclipse glasses that will allow you to watch the event, while protecting your eyesight.

You can also create a simple "pinhole" projection. It's as easy as making a small pinhole in a piece of paper or cardboard. Do not look through the hole, but allow the Sun to shine through and project an image onto a second piece of cardboard. Even a blank wall or clear patch of ground can make good surfaces for projection.

Sometimes nature helps out too. If you can see sunlight travelling through the leaves of a tree, you’ve got yourself some ready made pinhole projections. Check the ground and it might be covered with little crescent Sun images. Take a look at this great example on the Astronomy magazine website.

I’ve never seen a Total Solar Eclipse, so I'm heading up to Queensland for my first chance. I've been told that it's quite an eerie experience to have darkness fall while it's still early morning.

If you will also be in the path of totality for this eclipse, then be sure to check out the Eclipse Megamovie Project. Use your smartphone to upload images and videos of the Sun during totality and the Space Sciences Laboratory in California will combine the footage to create the first ultra-high time resolution movie of a solar eclipse.

What I'm most looking forward to is the chance to see the Sun's corona, the bright and tenuous gas that surrounds the Sun. Normally it's invisible, drowned out by the Sun's glare, but being able to see hidden things is something that's always captivated me about astronomy.

Solar Eclipse from 1999. During totality the Sun's diffuse corona and thin pink chromosphere can be seen.
Source: Luc Viatour. www.lucnix.be
 

Moon gazing across the globe

Author
by Nicole K
Publish date
22 July 2012
Comments
Comments (6)

Your Question: How can my wife and I gaze at the full moon together, but from opposite sides of the globe?

Our enquirer is in Jervis Bay, on the East Coast of Australia. His wife is in Ottawa, Canada. They contacted Museum Victoria to ask if we can help them plan a romantic evening – a full Moon-gazing date on opposite sides of the Earth.

A full moon seen from Ontario, Canada. A full moon seen from Ontario, Canada.
Image: Michael Gil
Source: Wikimedia Commons
 

The next full Moon will occur on the 1st or 2nd of August 2012 (depending on what time zone you are in). In Ottawa, the Moon will rise at 7:55pm EDT (Eastern Daylight Time) on 1 August. It will be at its absolute fullest at 11:27pm and will continue to be visible until it sets on 2 August at 6:28am.

Sadly in Jervis Bay's time zone, the full Moon will occur when the Moon is not visible from that side of the Earth, at 1:27pm AEST (Australian Eastern Standard Time). The Moon will have set that morning at 6:24 and will not rise again until 5:32 that evening.

All is not lost, however. The Moon-watching date can still occur, just not at the precise moment when the Moon is at its fullest. Our couple will just have to wait a few hours.

When the Moon rises on the night of 2 August in Jervis Bay (at 5:32pm AEST), it will be 3:32am in Ottawa (EDT). The Moon will be visible in both places and will remain so until it sets in Ottawa at 6:28am (EDT). This means our two Moon-gazers can watch the still-very-full Moon "together" for nearly 3 hours.

If the idea of getting up so early diminishes the romance from the Canadian perspective, our Moon-gazers can wait a few days – if they are happy to look at a Moon that is no longer full.

On 4 August, the Moon will rise in Jervis Bay at 7:38pm (AEST). It will be 6:02am in Ottawa (EDT). The Moon will be visible in both locations until it sets in Ottawa at 8:48am. Unfortunately this means the Canadian half of our Moon-gazing couple will be looking at the Moon during daylight (the Sun will rise in Ottawa on 4 August at 5:51am).

While arranging this date was tricky, it was only possible because our lovers are not on exactly opposite sides of the Earth. If they were, there would be no chance of viewing the Moon that the same time (for more than an instant and only then if they had a perfect view of the horizon). And one of them would have to be in a boat. Less than 4% of all land on Earth (and no part of the Australian mainland) is antipodal (diametrically opposite) to land: the antipode of Jervis Bay is in the North Atlantic Ocean; the antipode of Ottawa is in the Indian Ocean.

Maps showing Jervis Bay, Australia, and its antipode, in the North Atlantic Ocean. Maps showing Jervis Bay, Australia, and its antipode, in the North Atlantic Ocean.
Image: Antipodes Map
Source: Antipodes Map
 

Links

Melbourne Planetarium: Skynotes

Melbourne Planetarium: Moon Phases

US Navy: Rise/Set times for Sun/Moon

Antipodes Map

timeanddate.com

Seeing the Transit

Author
by Tanya
Publish date
29 June 2012
Comments
Comments (0)

It may just have been a little dot – but what a dot it was!

Breakfast with Venus was held at the Melbourne Planetarium as a special event for the Transit of Venus, selling out in just three weeks.

We were treated to a glorious morning, which was a great surprise as the days leading up to the event were dreadful, with constant cloud and rain.

Visitors watched Venus move onto the Sun via a live feed from Mauna Loa in Hawaii, made possible through a partnership with the Exploratorium, San Francisco. It was incredible to have a room full of silent people in our planetarium foyer, just waiting for the moment to see Venus' dark shadow appear. And it was just so brilliant when it did!

We then moved out to the Scienceworks arena where five telescopes were set up, including one projecting a large screen image. Everyone was able to see the moment again, but this time directly for themselves. We all had our eclipse glasses too and we were surprised at how easy it was to see Venus through them.

After getting our fill of Venus and some light breakfast, we headed into the Planetarium for a presentation describing the geometry of the transits – particularly why they come in pairs before having to wait over a century for the next one – followed by the highs and lows of previous transit expeditions.

Path of Venus across the Sun Transits of Venus come in pairs, one either side of the "sweet spot" where Venus' orbit crosses the ecliptic plane. By 2020, when Venus and the Sun are lined up again, Venus will fall short and miss the Sun.
Source: Museum Victoria
 

The human stories drew much collective laughter and sighs from our audience. Over the centuries astronomers have dedicated years of their lives to see this event. None more so than Jean-Baptiste Chappe d'Auteroche who saw the Transit of 1769 from a Spanish Mission in Baja California (what is now part of Mexico) but then passed away six weeks later as an epidemic spread through the area.

In the lead up to the 2012 transit, Guillaume Le Gentil became a bit of a 'poster boy' for the event. He was the one who saw a brilliant transit in 1761, but because he was stuck out at sea, he wasn't able to make any meaningful measurements. He managed to set up an observatory in India for the 1769 transit ...

"only to be the spectator of a fatal cloud which came to place itself before the Sun at the precise moment of my observation, to carry off from me the fruits of my pains and fatigues."

Fortunately for our transit, we were able to continue viewing the event throughout the day. A few hundred people saw Venus, with many commenting that they had taken time off work or kept children home from school to do so. I joined in too, and two of my sons were able to get out of school for a short while to share the moment with their mum.

Tanya with her sons A happy astronomer shares the Transit of Venus with her sons.
Source: Tanya Hill
 

I was amazed by the dedication of our visitors who were happy to wait for just another clear patch of sky so they could catch one more glimpse of Venus. And my final thought – what will the world be like when Venus next meets up with the Sun, in that far off December of 2117?

Partial lunar eclipse

Author
by Tanya
Publish date
2 June 2012
Comments
Comments (1)

Tonight the Moon, Earth and Sun will fall into line to create a partial lunar eclipse. Between the hours of 8pm and 10pm, a small section near the top of the Moon will plunge into the Earth's shadow.

This event has been somewhat overshadowed (ha! ha!) by the Transit of Venus that occurs on Wednesday. But I must say, that I have a particular love of lunar eclipses. I think it's because they happen at night - so not only do you get to see the eclipse, but you can also check out the starry night sky.

9pm, 4 June 2012 The eclipsed Moon will be found below the constellation of Scorpius, at 9pm on 4 June (created using the Starry Night software).
Source: Museum Victoria
 

This eclipse will occur in the eastern sky, with the Moon just beneath the constellation of Scorpius - one of the constellations that really is true to its name. Looking at the curving line of stars, it is easy to picture a Scorpion up there in the sky. And if you are away from city lights, then you'll see the brightest part of the Milky Way, which lies towards the Scorpion's tail.

The other great thing about lunar eclipses is that you don't need any special equipment at all to view them. Just a clear night sky and the willingness to spend some time outdoors, marveling that we are part of a much larger Universe.

Lunar Eclipse Sequence Progression from a partial to total lunar eclipse, Pennsylvania, December 2010.
Image: Anthony Skorochod
Source: Wiki Commons
 

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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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