Posted by: Dr. Breffni Lennon | June 16, 2012

Why the sky is blue: John Tyndall’s contribution to Rio+20

John Tyndall, as far back as 1861 (in his paper On the Absorption and Radiation of Heat by Gases and Vapours, and on the Physical Connexion of Radiation, Absorption, and Conduction) recognised that changes in the composition of atmospheric gases can ultimately bring about changes in the Earth’s climate. This occurs due to the ability of atmospheric gases to prevent a certain percentage of the sun’s rays from returning back into space, the concept now commonly known as “the greenhouse effect”. His later research on the effects of CO2 and water vapour in determining this phenomenon have continued to inform climate scientists ever since.

Tyndall is also credited with providing the first plausible explanation for why the daylight sky appears blue (Tyndall, 1868). Essentially, as sunlight passes through the atmosphere the particulates and pollutants that are present there scatter the blue end of the light spectrum sideways, allowing the red end of the spectrum pass through more or less unhindered. As the human eye looks into the sky it sees this process as blue light. The phenomenon he described is still called “The Tyndall Effect” to this day, in honour of him.

You can download his 1861 paper here, and you can download his 1868 paper here.

A short biography of John Tyndall by Prof. William Reville, UCC, can be accessed here.

References:

  • Tyndall, J. (1861) The Bakerian Lecture: On the Absorption and Radiation of Heat by Gases and Vapours, and on the Physical Connexion of Radiation, absorption, and Conduction. In Philosophical Transactions of the Royal Society of London, 151: 1-36.
  • Tyndall, J. (1869) On the Blue Colour of the Sky, the Polarization of Skylight, and on the Polarization of Light by Cloudy Matter Generally. In Proceedings of the Royal Society of London, 17: 223-233.
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