Olbers' Paradox; or why is the sky dark at night?

By Tim Hunter

"So familiar is the darkness of the sky at night that it is easy to forget its fundamental importance.”   Otto Struve 1963

 “The Olbers Paradox, formulated in the 19^th century, is still one of the most significant constraints on observational cosmology.”  Lajos Balazs 2004

Introduction:   Olbers and his life.

Heinrich Wilhelm Matthias Olbers (1758-1840) was born near Bremen, Germany and spent most of his life in Bremen.  Olbers was formally trained as a physician and is said to have developed a celebrated method for calculating cometary orbits while at the sickbed of a fellow student.  Olbers’ method for cometary orbits is still extensively used, and his original publication of cometary elements in 1797 was expanded in later editions by Encke in 1847 and Galle in 1864. 

Olbers practiced as a physician in Bremen from 1781 until retiring in 1823.  The upper portion of his house was fitted as an observatory, and he observed most clear nights.  It is said he never slept more than four hours.  He discovered the great comet of 1815, which is named for him.  He is also noted for his re-identification of Ceres and his discovery of Pallas and Vesta (Moore, 2002). 

Because of Olbers’ stature as an astronomer, his simple but entirely serious question “Why is the sky dark at night?” is now known as Olbers’ Paradox, even though he was not the first to ask this question or the first to seriously consider it (Moore, 2002).

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