Heinrich Olbers

Why might we be intrigued by an insomniac medical practitioner, active in the city of Bremen during the 18th/ 19th centuries? He seldom needed to sleep for more than four hours, allowing time for a nocturnal passion alongside his daytime attention to patients. Olbers was a serious physician, giving decades of care to his community, but also a talented astronomer.

Born in 1758 CE, the son of a pastor, from childhood he was an enthusiastic follower of science. Together with the medical curriculum, Olbers also took mathematics at the University of Göttingen. After gaining a medical degree, he established himself in Bremen, aged 23. The upper floor of his home was equipped as a private observatory.

A serious physician, giving decades of care to his community, but also a talented astronomer.

Comets and celestial mechanics

Before then, while still a student, Olbers devised an improved method for calculating the orbits of comets. His dexterity in cometary mechanics led to his engagement in a collective search for a planet that was believed to lie between the orbits of Mars and Jupiter. No singular body was ever found, but a multitude of rocky debris led to speculation that this might be the residue of a fragmented primordial world. The asteroid belt, as it is termed today, is now believed to have accumulated due to the massive gravitational influence of Jupiter, also explaining why Mars is not larger.

Pallas, Ceres, and Vesta

Here, a brief detour is worthwhile. While seeking the mystery planet, in 1802 CE Olbers isolated Pallas, just the second object to be found. In the preceding year, Guiseppe Piazzi had fleetingly found Ceres, now known to be the largest in the belt. Olbers located Pallas while trying to reacquire Ceres. He realised that neither Ceres nor Pallas were sufficiently large to be the missing planet, so he persevered, fruitlessly, but in 1807 CE pinpointed Vesta. These three represent the most substantial bodies of their kind. By then, a problem of terminology had arisen. None of these substantial rocks justified being designated as planets, leaving the scientific community to ponder nomenclature. A giant of the era, William Herschel, discoverer of Uranus, coined ‘asteroid’, a term that still stands. Derived from the Greek, meaning star-like. For context, the Moon is nearly four-times the diameter of Ceres and 80-times its mass.

Olbers’ paradox

Reverting to Bremen, Olbers continued to practise medicine and observe the heavens. Later, in 1823 CE, he became linked with an inquiry still known as Olber’s paradox. Simply stated, it asserts that the dark night sky demonstrates that stars are not evenly spread throughout an infinite, static universe. If that were so, at night, in every direction, the sky should become as radiant as the Sun. Although he remains associated with the issue, he was neither the first to pose it, nor the one who explained it. The credit perhaps belongs respectively to Thomas Digges and Lord Kelvin, from the 16th and 19th centuries. Digges also first elaborated the Copernican model in English. Kelvin’s deeds would fill a book; indeed, several exist.

Bessel and celestial scale

So, if Olbers and his peers never found their mysterious planet, and he neither raised nor resolved the eponymous paradox, how should he be regarded? Maybe his principal gift lies in another direction. Between finding Pallas and Vesta, Olbers noted the endeavours of a 20-year-old shipping clerk who had written a paper on Halley’s Comet. Its quality encouraged Olbers to set further astronomical projects for the young man. Olbers acted as his mentor. This led the protégé to relinquish commerce for astronomy. After 34 dedicated years, Friedrich Bessel determined the distance to a constellation named 61 Cygni. At about 11 light years, a near neighbour in the galaxy but humanity’s first realistic assessment of celestial scale.

Olbers life of 81 years meant he lived to witness this remarkable coup. Herschel’s son, the redoubtable John Herschel, described it as “the greatest and most glorious triumph which practical astronomy has ever witnessed”. Bessel’s ascent is surely Olbers’ enduring legacy.

RNP – The Herschel duo feature in Jimbo’s Assumption. Piazzi, Ceres, and Carl Friedrich Gauss’s feat in tracking the body, too. Bessel and Olbers figure in the sequel.