What causes a lightning bolt?


Bus Stop: Maria-Theresien-Straße  

The physicists at the University of Innsbruck know that high electrical voltages of up to one hundred million volts prevail in a thundercloud. The first dart leaders make their way towards the earth and thus prepare the lightning channel through which the negatively charged electrons race. The molecules of the air are thus charged positively, resulting in a glowing, bright plasma – lightning. This mixture of neutral and charged particles (electrons, ions, etc.), which can reach temperatures of up to 30.000°C, suddenly displaces the air in its surroundings. We all recognize the resulting loud bang as thunder.

Victor Franz Hess

Did you know that the electrical voltages in a storm cloud alone are not always enough for lightning and thunder to develop? Often the additional influence of cosmic radiation (these are fast particles from space) is needed in order to generate enough energy for the thundercloud to discharge. The physicist Victor Franz Hess – one of the four Nobel Prize winners of the University of Innsbruck, by the way – discovered this phenomenon as early as 1912. To further investigate this radiation he set up a measuring station on the Nordkette in the 1930s, which still exists today.

Hess Messstation

Victor Franz Hess in 1931 at his measuring station at the University of Innsbruck.

Hess Ballon

In August 1912, during a balloon flight, Hess demonstrated “that at an altitude of 5000m (ionizing) radiation is much stronger than on Earth". (Peter M. Schuster/Lily Wilmes, Unfassbare Strahlung. Werdegang zur Modernen Physik, Pöllau 2016, S. 103, 107.)

  Faculty of Mathematics, Computer Science and Physics

  Institute for Ion Physics and Applied Physics

  Victor F. Hess/Heinz T. Graziadei/Rudolf Steinmaurer, Untersuchungen über die lntensitätsänderungen der kosmischen Ultrastrahlung auf dem Hafelekar (2300 m), in: Bericht über die Tagung der Schweizerischen Physikalischen Gesellschaft, in: Helvetica Physica Acta 7 (1934), S. 669-670. (German)

  Data on Victor Franz Hess, University of Innsbruck (German)

  The Nobel Prize Winners of the University of Innsbruck (German)

 Photos Victor-Franz-Hess-Gesellschaft – Archiv, Pöllau

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