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BUT Scientists’ Work Featured on Cover of Nature
The photograph published on the cover of the prestigious British journal Nature in June 2009 was created by a process involving the complicated mathematical processing of dozens of images taken during a total solar eclipse on 1 August 2008 in Mongolia. It is the most sophisticated image so far created of the Sun’s corona in the visible light spectrum.
In recent years a team headed by Prof Miloslav Druckmüller of the Institute of Mathematics at BUT’s Faculty of Mechanical Engineering have been responsible for groundbreaking improvements in the use of mathematical methods for analysing images of the solar corona. The core members of the team are Prof Druckmüller and his daughter Hana Druckmüllerová; others include insPeter Aniol and Martin Dietzel from Germany, Vojtech Rušin from Slovakia, Constantinos Emmanoulidis from Greece, Ronald Royer from the USA and Eva Marková and Marcel Bělík from the Úpice Observatory in eastern Bohemia.
These new methods introduce a hitherto unprecedented degree of precision in the study of the Sun’s corona – the hot plasma “atmosphere” of the Sun, with temperatures in excess of one million kelvins. In the images it is possible to study the very complicated structures of the plasma modeled by the Sun’s strong magnetic pole. Analysis of the radiation of various iron ions provides very precise information about temperatures. The complicated processes taking place in the corona have a major effect on the Earth, and this has led to the great interest shown in them in recent years.
Approximately sixty total eclipses of the Sun take place in the course of a century, and these are only visible within a narrow band on the Earth’s surface, the path of totality. It often happens that the path of totality occurs in places highly unsuitable for observation, for example oceans or locations where weather conditions are generally adverse. For that reason, great care must be taken in the selection of an observation site. Among other things, in choosing these locations Prof. Druckmüller’s team makes use of maps indicating the long-term likelihood of clarity at the observation site.
On 1 August 2008 the zone of totality traversed Siberia, passing through the Altai mountain range and the Gobi Desert in Mongolia and China. Hana Druckmüllerová joined an expedition from the Úpice Observatory and observed the eclipse at Klyuchi in the Novosibirsk region. Prof Druckmüller was a member of a German-Czech-Slovak expedition in Mongolia that travelled in all-terrain vehicles from Ulan Bator to Bor-Udzuur in the Gobi Desert. Although the probability of good weather was only about 50 percent at both sites, both expeditions met with miraculously clear skies and were able to take exceptionally high-quality photographs of the Sun’s corona. It was from photographs taken in Mongolia that the image that appeared on the cover of Nature was created.
On 22 July 2009 the path of totality moved through India, China and the Pacific Ocean.
Hana Druckmüllerová was with astronomers from the Úpice Observatory and the Astronomical Institute of the Czech Academy of Sciences in Suzhou, west of Shanghai. Prof Druckmüller was on the small atoll of Enewetak in the Marshall Islands as a member of an American-German-Czech-Slovak expedition. At Suzhou it rained the whole day of the eclipse, but at Enewetak the weather was good enough to enable good quality photographs to be taken.
Hana Druckmüllerová and Miloslav Druckmüller observed their first total solar eclipse on 11 August 1999 near the village of Németkér in Hungary. On that occasion, the zone of totality passed very close to the Czech border. Afterwards, Miloslav Druckmüller processed unscanned photographs he had taken on a computer, because he felt that the original photos bore no relationship whatsoever to what he had actually seen with his own eyes. In 2002, Hana Druckmüllerová began to create the first program for the mathematically correct enhancement of the visual quality of photographs of the Sun’s corona, now referred to as Corona 1.0. She entered this program and the work that described it in a science competition for secondary school students, where she placed third in the Physics category at the national-level round held in Kadaň in May 2003; in 2004 she represented the Czech Republic at the Intel ISEF competition in the United States. Miloslav Druckmüller took over the program and extended it to today’s highly sophisticated form and developed a number of additional programs. Since then, Hana Druckmüllerová and Miloslav Druckmüller have presented papers on their techniques at a number of international conferences, among them the Solar Eclipse Conference 2004 in the UK, the Solar Eclipse Conference 2007 in the USA, the Corona and Plasma Physics Conference 2008 in Russia and the Dynamic Solar Corona 2009 in China.
The techniques used today by Hana Druckmüllerová and Miloslav Druckmüller for visualization of the structures in the solar corona make it possible to create the most faithful image of the corona attainable by any method currently employed. Many other methods damage the image of the solar corona by emphasizing only the radially-oriented structures while ignoring, for example, the crests of the loops. The number of photos used differs from case to case. Usually each camera takes several dozen photos in the course of the total eclipse. Then, shortly after this phase of the eclipse ends, there follow as many as several hundred calibration shots. At any given observation site, several cameras are employed, using lenses of varying focal lengths (thus creating images with varying degrees of detail), in some cases also in various spectral lines; this makes it possible subsequently to determine the distribution of various ions and atoms in the corona.
To process the photos of the solar corona taken during a total eclipse of the Sun, the members of Prof. Druckmüller’s team use a whole range of software programs; most were designed for a single purpose and in general they are their own, developed over the years. The BUT scientists have at their disposal a program for the calibration of photos taken during the eclipse with the help of calibration photos taken shortly after the eclipse; a program for the precise geometric alignment of the images; a program determining the precise centre of gravity of the Moon in the images, which is needed in order to make further calculations; a program for combining many photos with various exposure times into a single image with an immense dynamic range; a program for enhancing the visibility of coronal structures in images with a high dynamic range; and many other single-purpose programs. Most of them are the work of Prof Druckmüller.
The next total eclipse of the sun will take place on 11 July 2010 in the Pacific. Hana Druckmüllerová is preparing to observe the eclipse from Mangaia, the most southerly of the Cook Islands. This year Miloslav Druckmüller will again be part of an American-German-Czech-Slovak expedition. Their observation site is being kept a secret. Only a very few reasonably accessible islands are situated in the path of totality, so there is the threat that, should they reveal the name of the place from which they wish to observe the eclipse, the expedition would be outbid by a party with greater financial resources.