Wednesday, 04 July 2012

Advance Australian Astronomy Fayre

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Why send a man half way around the world to watch a sunspot?

TAHITI. June 1769. Lieutenant James Cook of HMS Endeavour is sitting on a beach. Around the bay where his ship is harbored are three of his companions, including the famous naturalist, Joseph Banks. In his hands are the instruments that will help him accurately determine the distance of the Earth from the Sun.

The reason Cook was sent on this junket was a rare astronomical event: the Transit of Venus. Occurring once every 120 years, the orbit of Venus passes between the Sun and the Earth, casting a shadow on the sun. Since the sun is many times the size of Venus, there is no eclipse, but Venus appears as a small spot on the face of the sun.

The nature of Venus’s path around the sun means that the transits occur in pairs, eight years apart, followed by a 121-year gap between the last transit pair and the next. Given the rarity of the event, it was a feat of planning and Cook’s navigational and sailing skills that propelled the unlikely group to this unlikely place for what was essentially a science experiment. In the process, Cook would lose his astronomer, Charles Green, to disease; they would circumnavigate New Zealand, discover many new Pacific Islands, and, most importantly for us, bump into the Great Barrier Reef on the East Coast of Australia.

The invention of the telescope revolutionized humanity’s perception of our place in the universe. Galileo observed moons orbiting Jupiter, Kepler predicted that the orbits of Venus could pass between the Sun and the Earth, and that these times could be pre-determined. Edmond Halley, he of the comet fame, was the first to observe the Transit of Mercury, the planet closest to the sun, and he predicted that the planet Venus would also transit not long after. He proposed that the principle of parallax could be used to determine the distance of the earth from the sun. That is, by recording the times when the transit started and finished at different locations on the planet, trigonometry could be used to determine this distance.

It was an age of discovery, of new lands on earth and new planets and objects in space. Meanwhile, new islands were being discovered in the Pacific and the race to find the theoretical southern continent, Terra Australis Incognita, began.

Cook was directed by both the British government and the Royal Society to travel to the Southern Hemisphere, ostensibly to observe and measure the 1769 Transit. But he was also given sealed orders, only to be opened after the Transit had been observed, to search for Terra Australis. Ancient philosophers including Aristotle had posited the existence of a great southern landmass to balance out the mass in the northern hemisphere Cook was directed to discover this landmass and claim it for the British Empire.

Arriving six weeks in advance of the Transit, Cook, Banks, Solander and Green built a fort and settled into a routine, if slightly uneasy life with the Tahitians. A few days before the Transit, some of the astronomical instruments were carried off by some of the Tahitians and had to be recovered by the resourceful Banks. On the day of the Transit itself, the sky was mostly clear. But Cook and the others observed a slight blurring of the edges of Venus, which made it difficult to perfectly measure its position. This made the measurement less accurate than expected. Once the measurements were complete, Cook and his crew left Tahiti (not without some regret, particularly on the part of Joseph Banks, a naturalist in more ways than one) and made their way westwards.

Fast forward more than two hundred years, to June 6th, 2012 when the last Transit of Venus for the 21st century would took place. It became a global celebration, with universities, observatories and workplaces all around the world geared up to watch it. In Australia, universities and research institutes held special events, while people bought solar filters for cameras and binoculars so they could observe the Transit as it happened.

At Mount Stromlo Observatory in the ACT, cosmologist Brian Tucker was astonished to find several hundred people queuing three hours in advance of opening time, just to catch a glimpse of the transit. “The Observatory was the first Commonwealth-designated building in Canberra.. built before anything else in Canberra…It’s something embedded I guess in the general knowledge..”

“Two years ago we started getting requests about the Transit of Venus.. We had six telescopes…and a projection onto the café wall. At lunchtime we had lines of an hour wait.. It was an amazing event. I actually didn’t even get to look through a telescope myself.” Tucker estimates that about 5000 people turned up to the viewing. At the Observatory and nearby ANU alike, people used any implement that would allow them to see the transit without damaging their eyesight. Striking images from live feeds and photographers, amateur and professional alike, appeared on Twitter, Facebook and live blog feeds attached to media sites around the world. Some of the most beautiful were those taken with solar filters, allowing us to see the surface of the sun – not smooth, but a fractured, textured surface, with solar flares and sunspots, and the tiny, black, vulnerable disc of Venus shadowed against it. Breathtaking.

The Mount Stromlo Observatory has become an essential part of the cultural life of Canberra, it’s partnered with Siding Spring, which is the “dark half” of Stromlo. As Canberra grew around the telescope, the resultant light pollution required Siding Spring to be built as a darker observation station. This is where most of Tucker’s data comes from.

The research carried out at Stromlo won Professor Brian Schmidt a Nobel Prize in 2011.

“We look at Type 1 [a kind of] supernova…we use to this to probe how the Universe is growing and what it’s made out of,” Tucker explained, when I asked about the other work they were doing at Stromlo. The work looks at how the Universe is expanding. “My project has been to figure out what is causing this expansion, and to find out what dark energy is…We calculate what the distance should be to the supernova, and then what the distance is to the supernova and using that difference, we calculate it [the density].” This ongoing work also suggests that one of Einstein’s theories which the scientist himself discarded as “nonsense,” the Cosmological Constant, may actually be correct. So Einstein may, in fact, always be right.

Stromlo and Siding Spring may soon get a new sibling. Australia is in the running to build a large optical telescope that, at 30m in diameter, would be three times larger than Stromlo. The addition of the Square Kilometer Array (SKA), an arrangement of radio telescopes to be jointly housed by Australia and South Africa, would allow for different kinds of measurements and processing power that haven’t been available to Australian astronomers before. It’s a chance to become something of an astronomy mini-super power to rival Chile and Hawaii’s Mauna Kea.

Telescopes like the SKA and the planned optical telescope will allow astronomers to look for planets in different parts of the sky. Currently, the Kepler spacecraft focuses on one part of the sky, day in, day out, looking for planets. Even if it’s one patch of sky, in cosmic terms, that’s an inconceivable amount of the Universe to look at. And how do astronomers find these other planets? By using the principles of planetary Transits. You can think of it this way: there are millions and billions of stars in the Universe. Focus on a tiny part of that universe with an observatory like Kepler. Then focus on a few of those stars to begin with. The stars are too far away for the most part to see a planet Transiting as we can see a planet transiting across out own star. But you can look for possible changes in the way the light is transmitted, if there’s an alteration or a change. Certain markers in the way the transmitted light changes can tell us whether there is a there is a planet orbiting that star. That can also tell us whether we should look more closely at the star in question. Thus, the planetary Transit can tell us much more than how far a planet is from its Sun.

Let’s travel back two hundred years again. On his return journey, having circumnavigated New Zealand and drawn maps that would be used for the next two hundred years, Cook nearly ran aground in the shoals of the Great Barrier Reef. He went ashore to repair the ship at what is now Cooktown. After successfully navigating Northern Queensland, he passed through the Torres Strait into Indonesia, then known as the East Indies, and beyond. He never returned to Australia. Although he was sent on a second mission to find Terra Australis, he concluded on this voyage that it didn’t exist. He did, however, recommend Botany Bay as a possible site for colonization. The rest, as they say, is history. On 26 January 1788, the First Fleet sailed into Botany Bay, and the modern era of Australia began. In some ways, we’re a nation born from astronomy.

In a fitting tribute to the grand mariner and scientist and one of the greatest terrestrial navigators this world has ever seen, the names of Cook’s principal vessels, Endeavour and Discovery, have graced two of NASA’s Space Shuttles. Cook’s legend had entered the space age.

Last modified on Wednesday, 01 August 2012
Upulie Divisekera

Upulie Divisekera is a cake-loving molecular biologist and science communicator with an evangelical interest in dinosaurs.

Follow her on Twitter @scienceupulie