Anders Celsius – A pioneer in investigating the Earth and its changes
- Anders Celsius was a Swedish astronomer (1701–1744) and a prominent scientist of the Enlightenment.
- He devised the temperature scale now known as the Celsius scale, with a range of one hundred degrees between the boiling point and the freezing point of water.
- In 1730, he became Professor of Astronomy at Uppsala University and contributed to its scientific development.
- He took the initiative to found the Uppsala Astronomical Observatory, which was completed in 1741.
- He took part in international expeditions and collaborations that strengthened Uppsala University’s links with European research.
°C, as we know, stands for degrees Celsius, but who was Celsius? Celsius was a pioneer in investigating the Earth and its changes through systematic observations and by collecting long series of numerical data on things such as temperature. He started this work in Uppsala in 1722.
Anders Celsius lived in 1701 – 1744; he grew up in a family of astronomers in Uppsala, but in rather poor circumstances. At the age of 28 he was appointed professor of astronomy, but his main interest was our own planet.
Celsius first undertook a study tour to Germany, Italy, France and England over four years, before participating in a French scientific expedition to the Arctic Circle for one year, and later founding an observatory in Uppsala (close to his mother’s restaurant). However, his life proved short; he died, unmarried but with many friends, of a lung disease at just 42. But what did he actually do?
Anders Celsius’s own thermometer, with 100 degrees at the freezing point and 0 degrees at the boiling point.
Zoom imageAnders Celsius’s meteorological diary for the years 1722–1731 – the beginning of one of the world’s longest temperature series.
A new, exact temperature scale
Celsius had since 1722 not only measured temperature but compared different thermometers and temperature scales. He found none of them reliable and therefore constructed, after much testing, his own temperature scale in 1742, defined by the freezing and boiling points of water at normal air pressure. The interval in between he divided into 100 degrees. Today this is the international unit for temperature.
Also regarding temperature Celsius had in mind the benefit for future generations; he expected a weather journal to be continued in Uppsala for all time. Today the temperature series of Uppsala commencing in 1722 is one of the longest in the world.
Already in the latter part of the 1700s, Celsius’s assistant Pehr Wargentin could make use of the temperature series to study climate changes, nowadays a highly urgent subject.
Arctic Circle expedition to measure Earth’s shape
Newton’s theories of gravitation and centrifugal force at this time were disputed. In Paris there were intense discussions for and against, and there were plans to solve the question by determining if the Earth due to the rotation was somewhat flattened at the poles. At this moment Celsius arrived there, and he suggested that the contemplated expedition should go to the Arctic Circle in Sweden, to the Torne valley.
Celsius now became a member of the French expedition which performed measurements at the Arctic Circle in 1736 – 1737, both towards stars in the winter cold and between mountain peaks during summer. Also gravity was measured there. The results were then compared with corresponding ones around Paris.
The expedition itself did not manage to solve the controversial problem, but together with earlier observations of other phenomena it made the balance in the discussion finally tip over in favour of Newton.
An observatory in Uppsala to strengthen science
Inspired by what he had seen in Paris and Greenwich, Anders Celsius felt that Sweden needed its own astronomical observatory. Upon his return from the Arctic Circle, he had a 16-page document printed in which he outlined all the scientific advances that a Swedish observatory would make possible. He also highlighted Uppsala as the obvious location for it:
“... and truly no place in the whole of Sweden could be more suitable for this purpose than Uppsala, the ancient capital of the whole of the Nordic region [...] The mother of all Swedish studies, and, in terms of its location, the very core and heart of the entire Swedish realm.”
– Anders Celsius argues in favour of building an observatory in Uppsala
He got his way, and the observatory was completed in 1741. The yellow building is still there, standing ”askew” in central Uppsala. Here Celsius worked for the rest of his short life, together with his diligent assistants Olof Hiorter and Pehr Wargentin. However, the observatory itself – a cube-shaped structure at the very top of the building – no longer exists.
The Celsius Observatory was replaced in 1853 by a new building in what is now known as Observatorieparken. In 2000, this was in turn replaced by an observatory situated on top of the Ångström Laboratory.
Zoom image“The Benefits of an Astronomical Observatory in Sweden” – the 16-page document that Anders Celsius had printed in 1739, setting out the case for building an observatory.
Zoom imageThe Anders Celsius Observatory as it looked when it was completed in 1741.
Celsius engaged in new methods using celestial bodies to determine latitude and longitude on the Earth’s surface, important for mapping, and he made the Uppsala Observatory the first zero meridian in Sweden. Together with Wargentin he made Uppsala internationally leading within longitude determination.
Celsius also could determine gravity in Uppsala, with a pendulum clock mounted in the Observatory and constructed by a specialist in London. This was one of only few gravity stations in the world at this time.
A link between northern lights and Earth’s magnetic field
When Celsius was in London he had, by the instrument specialist there, ordered a kind of large compass with an extra long needle. With this he studied, in Uppsala, variations in the direction of the magnetic field, pondering over whether they could be connected with phenomena in the atmosphere.
In winter 1741 Celsius and his assistant Hiorter noted that the magnetic needle behaved strangely when the northern lights appeared in the sky. Moreover, Celsius showed, through a cooperation with London, that a similar magnetic needle there behaved strangely at the same time as the one in Uppsala. Hiorter and Celsius had discovered that there had to be a connection between northern lights and the magnetic field.
Today this connection is fundamental for the understanding of the phenomenon of northern lights and the role played by the sun.
Land uplift – not water decrease
Celsius had early taken an interest in the phenomenon then called the water decrease, today known as the land uplift after the Ice Age, or the postglacial rebound. In 1743 he succeeded to determine its rate. For this he used an old seal rock, a rock where long ago seals could be shot when they rested close to the then mean sea level. The result was slightly more than 1 cm/yr, which is close to the correct value.
Based on this value, Celsius then drew the conclusion that large regions in Sweden must have been below sea level a few thousand years ago. He made natural science enter into history.
Celsius had, for the benefit of future generations, a special mark for the mean sea level 1731 cut into another seal rock. It turned out to be valuable one century later when it could be used to show that the phenomenon was a land uplift and not a water decrease.
Anders Celsius and Uppsala University today
Today’s research at Uppsala University in the fields of astronomy, geophysics and climate has clear, direct links to Anders Celsius. Perhaps most notably in the form of the unit we still use to measure temperature – in Uppsala and across the globe.
The temperature and weather measurements that Anders Celsius began in Uppsala in 1722 have continued uninterrupted ever since. Now the measurements are carried out at the Geo Centre. The series constitutes a very important dataset for today’s climate research.
The building that housed Anders Celsius’s observatory still stands today and reminds passers-by of Uppsala’s prominent position as a city of science. The observatory as a research infrastructure also still exists, in a modernised form, at the top of the Ångström Laboratory. Today, the observatory is part of the Department of Physics and Astronomy and is used in the research and teaching carried out there.
Text by Martin Ekman, reader of geophysics and author of the book “The Man behind ‘Degrees Celsius’: A Pioneer in Investigating the Earth and its Changes”, with additions by David Naylor, Uppsala University Communications Division.