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DISPLAYING POSTS TAGGED: astronomy (18)

November solar eclipse

Author
by Tanya
Publish date
1 November 2012
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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
 

Transit of Venus

Author
by Tanya
Publish date
29 May 2012
Comments
Comments (2)

On Wednesday 6th June, we have the chance to witness a rare astronomical event - a Transit of Venus. The Earth, Venus and the Sun will fall into line and we will see (with the appropriate equipment) Venus as a small black dot moving across the bright yellow Sun. The first Transit observed was in 1639, and there have only been five since, in the years 1761, 1769, 1874, 1882 and 2004.

"I recommend it therefore again and again to those curious astronomers who (when I am dead) will have an opportunity of observing these things, that they would remember this my admonition, and diligently apply themselves with all their might in making this observation, and I earnestly wish them all imaginable success …."

Edmund Halley, the astronomer made famous by Halley's comet, wrote those words in 1716. He was sixty years old at the time and was well aware that he would not live to see a Transit in his lifetime. But he had discovered that this rare event would unlock the scale of the Solar System and so he urged future astronomers to make good use of his findings and wished them " immortal fame and glory."

You see, back then we knew the relative distances of the planets – Mercury is almost 3 times closer to the Sun than Earth, Saturn is 10 times more distant – but we didn’t know their true distances. The key was the Earth-Sun distance, astronomers call it the Astronomical Unit, and Halley had realised that this could be measured during a Transit of Venus.

Observations of the transit from different locations across the world would differ slightly – some would see Venus travel a short path, moving onto the Sun later and leaving earlier than would be seen elsewhere. By timing the planet's journey and adding in some trigonometry (the mathematics of triangles) the Earth-Sun distance could be measured and everything else would fall into place.

 

Transit from space The path of Venus across the Sun varies slightly when viewed from different locations on Earth. Image is not to scale.
Source: Museum Victoria
 

Astronomers of the 18th Century took up Halley's call but the world was a much bigger place back then. The southern hemisphere was largely unexplored – Captain Cook observed the 1769 transit from Tahiti then went on to undertake the historic mapping of Australia’s east coast.

And no one can forget the tenacious efforts of the French astronomer Guillaume Le Gentil. The Seven Years War was underway and after more than a year of traveling across treacherous seas Le Gentil was unable to reach land in India because it had been taken over by the enemy, in this case the British.

In fact, Le Gentil’s story is heartbreaking. He had brilliant viewing conditions for the 1761 transit, but because he was stuck out at sea with no means of determining his location (ie. longitude) nor an accurate clock for timing the event, his observations didn't mean a thing. What he would have given for a smartphone with GPS!

Amazingly, Le Gentil decided not to go home but to wait out the next 8 years for another Transit. He built an observatory, survived a severe illness, and was fully prepared for the day, only to be beaten by the weather. When he did return to Paris eleven years later, he had been presumed dead – his wife had remarried, his estate was gone and he’d lost his seat at the Royal Academy of Science. Not exactly the fame that Halley had imagined.

Those early astronomers by solving the scale of the Solar System, were also helping us to understand the Sun. By knowing its distance, we could confirm the Sun's size, mass and intrinsic brightness. What’s more, they were also setting us up to determine the extent of the entire Universe. The Earth-Sun distance is the baseline for measuring the distances to nearby stars. A series of stepping stones then takes us distance hopping across the Universe – all the way from star clusters to galaxies near and far.

So next month, when we have the chance to witness the last Transit of Venus for this century, I urge you to heed Halley’s words. It may not be a glitzy show but it’s our connection to both the Universe around us and a piece of our history. And just like those astronomers of the past, we can take a moment to wonder what the world will be like by the time the next Transit rolls around for that far-off December in 2117.

UPDATE: Scienceworks' special Breakfast with Venus from 8am to 10am on Wednesday 6th June is now sold out.  

2004 Transit Venus transiting the Sun in 2004
Image: Hugh Gemmell
Source: Hugh Gemmell

Links:

Transit of Venus

Transit of Venus app for iPhone and Android

Transit of Venus: 1631 to the present by Dr Nick Lomb, published by Sydney Observatory.

Science in the South Seas exhibition at the National Museum of Australia

Mesopotamian lunar table

Author
by Martin Bush
Publish date
25 May 2012
Comments
Comments (0)

Martin is the programmer at the Planetarium at Scienceworks.

A personal highlight for me in The Wonders of Ancient Mesopotamia exhibition is the Babylonian lunar table. I love this artefact not just because of the antiquity of its writing or how long it lay preserved in the ground, and certainly not just because of the skill needed to make the rows of tiny cuneiform script. (How did they do it? I could never have managed.)

Babylonian lunar table Lunar table K.90 from the British Museum on display in The Wonders of Ancient Mesopotamia.
Source: © The Trustees of the British Museum
 

This tablet is exciting because shows just how seriously Mesopotamian cultures took astronomy. Observers recorded the appearance of the Moon – and also the stars and planets – every single night of the year. (Ok, unless it was cloudy.) They sent reports of these observations to the king. Babylonian astronomers had centuries of astronomical observations to work with. Unfortunately we don’t as not so many of these reports have survived.

Some concerns of these ancient astronomers – like making horoscopes to advise the king – are no longer of much interest to modern astronomers. But many ancient achievements live on to this day. Astronomers still number lunar eclipse using a system known as the Saros Cycle. This cycle was discovered by Babylonian astronomers around the 5th century BCE.

The work of these Babylonian astronomers can also be seen in the Jewish calendar. Sometime around the 4th Century BCE Mesopotamian astronomers calculated the average length of the lunar month. The extensive observations they had to work with meant that they came up with a remarkably accurate figure, different to the modern value by only a fraction of a second. This value was taken up by Greek astronomers such as Ptolemy and from there it was incorporated into the Jewish calendar when it was codified in the first millennium CE. The value determined by Babylonian astronomers is still used today to determine the date of the Jewish New Year.

This lunar table survived for centuries in the ground while the influence of Mesopotamian astronomy on our study of the skies has lasted even longer.

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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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