Anders Celsius

Anders Celsius was a Swedish astronomer, physicist, and mathematician whose work in observational astronomy and scientific instrumentation left a lasting legacy in the physical sciences. Born on 27 November 1701 in Uppsala and active during the Swedish Age of Liberty, he contributed significantly to geodesy, photometry, and geomagnetism, and he established the temperature scale that later bore his name. As professor of astronomy at Uppsala University and founder of the Uppsala Astronomical Observatory, Celsius occupied a central position in the scientific life of eighteenth-century Sweden.

Early Life, Family Background, and Education

Celsius grew up in an academic environment. His family estate, Doma in Hälsingland, gave rise to the Latinised surname “Celsius,” meaning “mound.” His lineage included several prominent scholars; his father Nils Celsius was professor of astronomy, his uncle Olof Celsius was a noted botanist, and his grandfather Magnus Celsius was a mathematician. Another ancestor, Anders Spole, had also served as professor of astronomy. This intellectual inheritance encouraged an early aptitude for mathematics and the natural sciences.
He studied at Uppsala University, where he later rose to the chair of astronomy in 1730. His extended family included the poet and actor Johan Celsius, reflecting the broader cultural milieu from which he emerged.

Scientific Career and Astronomical Research

Celsius’s early work centred on improving astronomical observations and understanding large-scale measurements of the Earth. In 1730 he published a method for calculating the distance from the Earth to the Sun, contributing to celestial measurement techniques of the period.
He undertook significant research into geomagnetic phenomena. Working with Olof Hiorter, he systematically observed variations in magnetic compass needles and was the first to propose a consistent link between magnetic disturbances and the aurora borealis. His publication Observations of the Aurora Borealis (1733), comprising 316 recorded events from 1716 to 1732, became an important reference in early auroral science.
Between 1732 and 1735 Celsius travelled widely, visiting major observatories across Germany, Italy, and France. During his stay in Paris he advocated measuring a high-latitude arc of the Earth’s meridian to test Newton’s hypothesis that the Earth is flattened at the poles. This proposal led to his participation in the Lapland expedition of 1736, organised by the French Academy of Sciences under Pierre-Louis Moreau de Maupertuis.

The Lapland Expedition and Geodesy

The purpose of the Lapland expedition was to determine the length of a degree of latitude near the Arctic Circle and compare it with results from a similar expedition near the equator in Peru. Celsius’s involvement was crucial both for scientific precision and for local knowledge of the region. The successful measurements confirmed Newton’s theory of a polar flattening, marking one of the great achievements in eighteenth-century geodesy.
After returning from Lapland, Celsius published Observations on Determining the Shape of the Earth (1738). His contribution earned recognition from Swedish authorities and helped secure funding to establish a modern observatory in Uppsala.

Uppsala Astronomical Observatory

Celsius founded the Uppsala Astronomical Observatory in 1741, equipping it with advanced instruments acquired during his travels. The observatory became one of the leading northern European centres for astronomical research. He conducted detailed studies of eclipses, variable stars, and stellar magnitudes, producing a catalogue of around 300 stars measured using his own photometric system, which achieved an accuracy of approximately 0.04 magnitude.

The Celsius Temperature Scale

In 1742 he proposed a new temperature scale to the Royal Society of Sciences in Uppsala. Celsius defined the freezing point of water as 100 degrees and the boiling point as 0 degrees, creating an inverted scale intended to accord with his observational methods. One year after his death, Carl Linnaeus reversed the scale for practical use, fixing 0 degrees at the freezing point and 100 degrees at the boiling point. This modified version became the modern Celsius scale, now one of the standard units of thermometric measurement.

Geographical and Geophysical Observations

Celsius conducted numerous land surveys as part of Sweden’s national mapping programme. He was among the first to observe that the land in Scandinavia was gradually rising relative to sea level, a phenomenon now known as post-glacial rebound. Although he initially attributed this change incorrectly to water evaporation, his systematic observations provided early evidence for the long-term geological processes affecting the region.

Scientific Societies and Final Years

From 1725 Celsius served as secretary of the Royal Society of Sciences in Uppsala. He supported and helped name the Royal Swedish Academy of Sciences, founded in 1739 by Carl Linnaeus and other scholars. His correspondence and involvement in scientific institutions attest to his broad engagement with contemporary European science.
Celsius died of tuberculosis on 25 April 1744 at the age of forty-two. Despite his short life, his scientific influence was considerable, extending from astronomy and geodesy to one of the world’s most widely used temperature scales.