Celsius was professor of astronomy at Uppsala University from 1730 to 1744, and in 1740 he built the Uppsala Observatory. In 1733 Celsius published a collection of 316 observations of the aurora borealis (aurora), or northern lights, made by himself and others from 1716 to 1732. He advocated the measurement of an arc of a meridian in Lapland and in 1736 took part in an expedition organized for that purpose, which verified Isaac Newton (Newton, Sir Isaac)'s theory that the Earth is somewhat flattened at the poles. In 1742 he described his thermometer in a paper read before the Swedish Academy of Sciences. His other works include Dissertatio de Nova Methodo Distantiam Solis a Terra Determinandi (1730; “A Dissertation on a New Method of Determining the Distance of the Sun from the Earth”) and De Observationibus pro Figura Telluris Determinanda in Gallia Habitis, Disquisitio (1738; “Disquisition on Observations Made in France for Determining the Shape of the Earth”).