1899 in science
The year 1899 in science involved some significant events, listed below. Astronomy December 2 – During the new moon, a near-grand conjunction of the classical planets and several binocular Solar System bodies occur. The Sun, Moon, Mercury, Mars and Saturn are all within 15° of each other, with Venus 5° ahead of this conjunction and Jupiter 15° behind. Accompanying the classical planets in this grand conjunction are Uranus (technically visible unaided in pollution-free skies), Ceres and Pallas. The 80 cm refracting telescope is completed at Potsdam Observatory. Biology May 1 – The National Trust in the United Kingdom acquires its first part of Wicken Fen, making it the country's oldest wetland nature reserve. November 8 – The New York Zoological Society opens the Bronx Zoological Park to the public in New York City under the direction of William Temple Hornaday. Chemistry Actinium is discovered by André-Louis Debierne. International Committee on Atomic Weights established. Exploration January 23 – The British Southern Cross Expedition crosses the Antarctic Circle. Later in the year, it first charts Duke of York Island. Mathematics Élie Cartan first defines the exterior derivative in its modern form. David Hilbert publishes Grundlagen der Geometrie, proposing a formal set, Hilbert's