In 1732 he began his grand tour and visited almost all of the notable European observatories of the day, where he worked with many of the leading 18th century astronomers.
Celsius went on an expedition with the French astronomer Maupertuis. The expedition was to measure the length of a degree along a meridian, close to the pole, and compare the result with a similar expedition to Peru near the equator. The expedition established Newton's belief that the shape of the earth is an ellipsoid flattened at the poles.
Anders, although an astronomer, participated in the geographical measurements for the Swedish General map. What he is known for today mostly is his Celsius thermometer, which was designed so that zero was the boiling point of water and 100 was the freezing point. The scale was later reversed to the form it is today.
In astronomy he made many observation of eclipses and made published catalogues of carefully determined magnitudes for a total of 300 stars using his own photometric system. His system was used by looking through glass plates at the star and keep adding plates until you can no longer see the light. This determined the magnitudes. The brightest star, Sirius, used twenty-five plates.
Anders Celsius died of tuberculosis in April 1744, only 42 years old. His grave is next to his grandfather's, Magnus Celsius, in the church at "Gamla Uppsala".