Astronomy in the deep freezeAstronomers are going to the coldest place on Earth to search for the heat radiated by distant objects in the universe.
Key text
Back to basics You will get more from this topic if you have mastered the basics of electromagnetic radiation and the solar system – this link will take you to an annotated list of sites with helpful background information. Key text‘Great God, this is an awful place’, explorer Robert Falcon Scott recorded in his diary during his trek to the South Pole in 1912. Tragically, his words turned out to be true. Bitter cold and starvation killed him and his team before they could return from their epic journey.Paradoxically, the extreme conditions that made life so difficult for the early explorers are now attracting astronomers to Antarctica: Australian researchers are proposing to build a permanent telescope on Antarctica's high inland plateau (Box 1: The Douglas Mawson Telescope).
Why go to Antarctica?
Most of us know that Antarctica is the coldest continent, but few know that it is also the highest and driest continent. These extremes of temperature, elevation and aridity are assets to those who study a particular branch of astronomy known as infrared astronomy (Box 2: A different window on the universe). Antarctica’s weather offers another advantage. The presence of a high-pressure system over the continent promotes predominantly stable, clear weather. This, combined with the absence of daylight in winter, allows for extended periods of continuous infrared observation of astronomical objects.
What is infrared astronomy?
Infrared astronomy is the detection and study of infrared radiation emitted by objects in space. Over 200 years ago a British astronomer, William Herschel, discovered that the sun emitted infrared radiation. Since then, infrared astronomy has increased in importance as more sensitive instruments to detect infrared radiation have been developed. Astronomers have found that infrared telescopes are better suited for studying certain types of objects than traditional optical telescopes or the relatively new radio telescopes.
What has infrared astronomy discovered so far?
Astronomers have discovered a great deal about the universe by using infrared telescopes. They can look at weather patterns on planets in our solar system, as well as determine the abundance and composition of their atmospheres. They have also discovered new comets and asteroids within our solar system. Infrared astronomers are discovering planets elsewhere in the Milky Way. It is not possible to see the visible light from these planets because it is swamped by the brightness of the star it orbits. In the infrared, where planets have their maximum brightness, the brightness of a star is reduced, making it easier to detect a planet. Most stars with a mass lower than our sun are less bright and much cooler and emit most of their energy in the infrared. These red dwarf stars are much more plentiful than stars heavier than the sun. Infrared astronomy has also played a key role in the search for very low mass stars known as brown dwarfs. Infrared astronomers have also found that the vast reaches of interstellar space are not completely empty. Clouds of tiny dust grains between the stars absorb visible and ultraviolet light and obscure our view of distant parts of the Milky Way. However, they can be observed at infrared wavelengths. Recent observations have revealed clear evidence of objects moving around a massive, invisible source – believed to be a black hole – with a mass over a million times that of the sun. Further afield, infrared astronomers are studying the most distant objects in the universe. Distant galaxies are much fainter and appear much redder than nearby ones. The reddening is caused by the expansion of the universe. Because it takes billions of years for light to reach us from the most distant galaxies, we see them as they were when they were young, not as they are now. During this time space itself has expanded and the wavelength of the radiation has been stretched or ‘redshifted’ by a large amount. As a result, a galaxy is more easily detected and studied in the infrared than at visible wavelengths.
Infrared down under
Infrared astronomy in Australia made its start in the early 1970s when a group at the Mt Stromlo Observatory in Canberra made the first infrared observations of the southern skies. Later a new type of infrared detector was installed at the Anglo-Australian Observatory in New South Wales and it was used in studies such as imaging the surface of Venus, observing molecular hydrogen in planetary nebulae and mapping the complex structure in the central region of our galaxy. Although infrared astronomy continues to flourish in Australia, astronomers are hampered by the lack of world-class observing sites because Australia has no really high mountains. Observatories established by American and European astronomers on mountain tops in Hawaii and Chile provide conditions for infrared astronomy far superior to anything available in Australia. But the high Antarctic plateau now offers Australia an ideal observing site. In 1993 a joint US-Australian team began a site-testing program at the Amundsen-Scott station at the geographic South Pole. Later a small, mobile Automated Astrophysical Site Testing Observatory began gathering data to select the best site for a permanent infrared telescope. The results from the remote-controlled observatory have confirmed that the best location on the Earth’s surface for infrared astronomy is undoubtedly Antarctica. Australian astronomers have also been using a small infrared telescope operated by US astronomers at the South Pole – the telescope has already produced some of the sharpest infrared images ever taken. Now Australian astronomers are proposing to build a telescope three times larger than the American one, which would enable astronomers to scan much larger sections of the sky. Australia’s Antarctic telescope is to be known as the Douglas Mawson Telescope (Box 1).
Future prospects
In addition to the astronomical advantages, a facility such as the Douglas Mawson Telescope would promote international cooperation and help strengthen the Antarctic Treaty. On another level, operating a facility in such extremely harsh conditions could be a dress rehearsal for eventually establishing an outpost on the moon or on a planet such as Mars. Perhaps the infrared astronomers are showing us that ‘this awful place’, as described by Robert Scott, is nothing less than a stepping stone to the wider universe. Related Nova topic: The Southern Ocean and global climate
In 1954 Australia established its first permanent base in Antarctica and named it Mawson Station, in honour of the pioneering explorer. Now, almost fifty years later, the explorer seems set to be honoured again with plans for the Douglas Mawson Telescope. The telescope would establish Australia’s first permanent facility on the high Antarctic plateau, where most of the Australian territory lies. The facility will be open to astronomers from Australia and overseas. Potential international partners include the United Kingdom, Germany, New Zealand and Argentina.
Features of the telescope
The diameter planned for the telescope is 2 metres, much larger than any existing telescope in Antarctica. The astronomers themselves will construct most of the detectors and other instruments required for the telescope. Importantly, the telescope can be loaded into a Hercules aircraft and transported from Australia to the Antarctic plateau. The diameter of the telescope will be only half that of the 4 metre Anglo-Australian Telescope (AAT) at Siding Spring Mountain in New South Wales. Although the AAT makes observations at both optical and infrared wavelengths, it has to cope with a relatively turbulent atmosphere that distorts the images under investigation. The observing conditions in Antarctica are so good that the performance of the Mawson telescope is expected to rival that of the AAT and other large telescopes in more temperate parts of the world, including 8 metre telescopes currently under construction in Hawaii and Chile. There are likely to be attractive commercial spin-offs from building the telescope. Australian astronomers are at the forefront of designing and building instruments for their telescopes. With billions of dollars being invested in astronomical facilities worldwide, there is a growing and lucrative export market for Australian instruments and expertise.
South to the deep freeze
The likely site of the new telescope is at a location known as Dome C on the high plateau in the Australian Antarctic Territory, 1600 kilometres from the South Pole. The plateau has an average elevation of 3000 metres (higher than Australia’s highest mountain Mt Kosciuszko), rising to 3250 metres at Dome C. Strong winds are relatively rare here in the centre of the continent. (Antarctica’s famous blizzards are mainly a coastal phenomenon caused when snow is whipped up by cold, dense air cascading off the high interior plateau.) The site at Dome C will be home to a major new French-Italian scientific base, Concordia Station, currently under construction. Astronomers and support staff reach the site by aircraft, departing from Australia’s Casey station.
Challenges ahead
A feature of the Douglas Mawson Telescope will be its wide field of view, enabling it to scan large sections of sky and quickly locate objects of interest. While larger and more expensive telescopes elsewhere can detect infrared radiation from more distant objects, their narrow field of view makes it difficult for them to make the initial discovery of these objects. The Mawson telescope will also play the role of a ‘finder’ telescope, locating previously unseen objects for other larger telescopes – both ground-based and in space orbit – to observe in more detail. The telescope will have a busy research program ahead. Of particular interest are events such as the birth of galaxies and their subsequent evolution. Another tantalising prospect is the study of the formation of individual stars and planetary systems in our own Milky Way. This may hold the key to how our solar system formed approximately 5 billion years ago and give some idea of the likelihood of Earth-like planets elsewhere in our Galaxy. Related sites
Infrared imaging is widely used in medicine, fire fighting, police and security work, and by the military. Infrared satellites are used to monitor the weather, to study vegetation patterns and geological formations, and to measure ocean temperatures. Infrared radiation is simply another form of electromagnetic radiation, similar to visible light and radio waves, but differing in its wavelength (or frequency). Infrared wavelengths begin in the ‘near’ infrared at around 0.0007 millimetres, just beyond the reddest light that the human eye can see, and grow in size to about 1 millimetre in the ‘far’ infrared. Wavelengths longer than this belong to the sub-millimetre, microwave and radio parts of the electromagnetic spectrum. Different types of telescopes are required to view the universe through these other ‘windows’ of the spectrum. Infrared radiation is emitted by any object with a temperature above absolute zero (-273ºC). In other words, the object radiates heat. Basically, all objects in space emit some infrared, but the wavelength at which the object radiates most intensely depends on its temperature. A very hot object has its peak emission near the middle of the wavelength range of visible light. As the object cools, the wavelength of peak emission moves to longer wavelengths (infrared). Very hot objects, such as stars, dominate views of the universe at wavelengths of visible light, but they are much less prominent at wavelengths of infrared. Objects in space emit radiation at all wavelengths across the electromagnetic spectrum. However, most of this radiation does not reach the Earth’s surface. Fortunately for life on Earth, the atmosphere blocks out harmful high energy radiation such as gamma rays and X-rays, and most ultraviolet rays. It also blocks out radio waves with long wavelengths and most infrared radiation. However, the atmosphere lets through visible light, most radio waves, and narrow ranges of infrared wavelengths, allowing astronomers to view the universe through these wavelength windows.
Pros and cons of infrared
Most of the infrared radiation reaching Earth is absorbed by water vapour (H2O), carbon dioxide (CO2) and ozone (O3) in the atmosphere. Only in a few wavelength ranges can the radiation make it through to ground level. Overcoming this limitation is the greatest challenge faced by infrared astronomers. Besides blocking out most infrared radiation, the Earth’s atmosphere poses another tricky problem. The atmosphere is warm and radiates strongly in the infrared, often swamping the astronomical object being observed. For the infrared astronomer, the sky itself glows brightly day and night. Thus, the best view of the infrared universe is at wavelengths that pass easily through the Earth’s atmosphere and where the background radiation from the atmosphere itself is at a minimum. For this reason infrared observatories are usually placed near the summit of high mountains to get above as much of the atmosphere as possible. Low temperatures at mountain summits are also an advantage because they cause water vapour to condense out of the air. Despite these difficulties, infrared observations are important for several reasons. Infrared radiation passes through the vast gas and dust clouds in interstellar space more easily than visible light, revealing objects hidden from optical telescopes. For example, young stars are usually surrounded by a cocoon of gas and dust. This makes them invisible at optical wavelengths, but their heat warms the dust grains and produces infrared radiation to reveal their presence. Related sites
Australasian Science April 2006, pages 29-33 Diary of an Antarctic astronomer (by John Storey) Includes the diary entries of an Australian astronomer spending the summer in Antarctica.
November/December 2004, page 6 Earth's best view of the universe (by Stephen Luntz) Discusses why Dome C in Antarctica is the best place on Earth for astronomy.
November/December 2004, page 6 Super telescope to be built of ice (by Stephen Luntz) Highlights some of the construction features possible for a telescope in Antarctica.
May 2003, pages 22-26 Diary from the Antarctic Plateau (by John Storey) John Storey spent most of January 2003 determining the suitability of two sites for Antarctic astronomy
June 2002, pages 20-25
Australian Antarctic Magazine Spring 2005, page 8-9 New telescope aids climate studies (by Andrew Klekocuik, John Innes and Andrew Cunningham) Explains how the Light Detection and Ranging (LIDAR) telescope is used to collect data about climate processes.
Autumn 2005, pages 8-9 New space weather telescope (by Marc Duldig) A telescope to be built in Germany will monitor sun activity.
Ecos No. 92, 1997, pages 15-20 Into the black (by Helen Sim) Describes the first space radio telescope.
New Scientist 18 September 2004, page 15 Pole position (by John Storey) Argues that a telescope in Antarctica makes better sense than one out in space, or anywhere else on Earth.
15 September 2004 Starry nights clearest in Antarctica (by Emma Young) Describes some of the advantages of the position of Dome C in Antarctica.
16 December 2000, pages 26-29 Universe in the balance (by Jeff Peterson) Describes how telescopes in Antarctica are used to determine the weight of the universe.
Inside Science (No. 133), 16 September 2000 Origin of planetary systems (by Robert Adler) Explains how planets form.
Provides a variety of information about infrared radiation and infrared
astronomy. 'What
is infrared?' includes an explanation of infrared radiation and where
it fits into the electromagnetic spectrum; 'Infrared
astronomy' has a definition and explanations (includes images); and
'Images
and videos' has a collection of images from a variety of fields, with
explanations of the information gained from the images.
Australian Broadcasting Corporation (transcripts)
Going to the ends of the Earth (The Astronomical Society of the Pacific, USA) Explains why the South Pole is a premier observatory site, and describes the research of the Center for Astrophysical Research in Antarctica (CARA) and the Antarctic Muon and Neutrino Detector Array (AMANDA).
Pluto's spic and span moon (The Why Files, USA) A chatty description of what astronomers found out about Charon, Pluto's moon, using infrared telescopes. Also covers other uses of these telescopes.
Infrared astronomy: in the heat of the night (J W V Storey, 1999 Ellery Lecture, Astronomical Society of Australia) Outlines the importance of infrared radiation to astronomers, traces some of the key Australian developments, and looks at the future of the field.
Australian Antarctic Division
Antarctic region (University of Texas, USA)
A clear map of the Antarctic region. The site proposed for the Douglas Mawson Telescope is 1600 kilometres from the South Pole, directly inland from Australia's Casey station.
Australian telescopes
brown dwarf. An object in space, intermediate in mass between a small star and a large planet. Brown dwarfs are very difficult to detect because they are very faint; as they age and cool they become even fainter. The radiation they emit is primarily in the near infrared. For more information see Brown dwarfs (Chandra X-ray Laboratory, USA). electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA). electromagnetic spectrum. The complete range of frequencies (or wavelengths) of electromagnetic radiation. For more information on electromagnetic radiation and the electromagnetic spectrum see Measuring the electromagnetic spectrum (High-Energy Astrophysics Learning Center, Goddard Space Flight Center, USA) and More about the electromagnetic spectrum (High-Energy Astrophysics Learning Center, Goddard Space Flight Center, USA). galaxy. Huge regions of space that contain hundreds of billions of stars, together with planets, glowing nebulae, gas and dust. infrared. The part of the electromagnetic spectrum between visible light and microwaves. The wavelength of infrared light is between 0. 7 micrometres (0.0007 millimetres) and 1 millimetre. These wavelengths are longer than those of visible light, but shorter than those of microwaves. (The prefix 'infra' means 'below; infrared refers to radiation below the frequency of red light.) infrared telescope. A telescope designed to observe in the infrared section of the electromagnetic spectrum. Infrared telescopes look like optical reflecting telescopes and operate in a similar way. The infrared radiation is collected and focused by mirrors onto detectors sensitive to infrared. One problem with infrared telescopes is that the telescope itself is a source of unwanted infrared radiation, but this is minimised by cooling the components of the telescope with liquid nitrogen for near infrared observations and with liquid helium for the far infrared. near, mid and far infrared. Infrared radiation is often subdivided into three regions – near, mid and far. Near infrared includes shorter wavelengths of infrared radiation, closer to visible light; far infrared includes longer wavelengths of infrared radiation, closer to microwave radiation. For more information see Near, mid and far infrared (Infrared Processing and Analysis Center, USA) optical telescope and radio telescope. Telescopes are instruments that are used to observe radiation from a distant object. They can produce an image of the object or enable the radiation to be analysed. Optical telescopes are used to observe wavelengths of visible light. They make distant objects distinct and visible by producing a magnified image of the object and by collecting more light than the naked eye. There are two main types of optical telescopes: refracting telescopes use lenses and reflecting telescopes use mirrors. Radio telescopes are used to observe longer wavelengths of radiation (radio waves), with large dishes to collect and concentrate the radiation onto antennae for detection. For more information see It takes more than one kind of telescope to see the light (Science@NASA, USA). red dwarf. A small, very faint and cool dwarf star. It is thought that red dwarfs are the most common star in the universe. For more information see A galaxy dweller's guide to planets, stars and dwarfs (Space Telescope Science Institute, USA)
External sites are not endorsed by the Australian Academy of Science. Page updated July 2006. The Australian Foundation for Science is also a supporter of Nova.
This topic is sponsored by the Australian Government's National Innovation Awareness Strategy.
|
