The above image shows a monument dedicated to Tycho Brahe (left) and Johannes Kepler (right). The monument is located in Prague, Czechia. Image Credit: WikiCommons contributor "Mohylek." This image is in the Public Domain.
Danish nobleman and astronomer Tycho Brahe (1546 - 1601) spent much of his life making very careful measurements of the positions of stars and planets. His work yielded data with an accuracy that was not previously possible. Brahe wanted his observations to be the basis of a new and more accurate set of star tables. He trusted this work to his collaborator, whom some considered his competition, the German mathematician, astronomer and astrologer Johannes Kepler (1571 - 1630).
Kepler was able to prepare the new tables using a combination of Brahe's accurate observations, a heliocentric (sun-centered) model of the solar system and Kepler's own discovery that the planets moved in elliptical (not circular) orbits. Following Brahe's death, Kepler faced many obstacles in completing the work. His biggest were Brahe's surviving relatives, who fought Kepler for the publication rights.
In 1623, Kepler at last completed the new tables. However, publication was delayed because of the publishing requirements of Emperor Ferdinand II and because of ongoing negotiations with Brahe's family. In the meantime, religious tension — the root of the ongoing Thirty Years' War — put Kepler and his family in jeopardy. In 1626, Kepler and family moved from Bohemia to Ulm, Upper Austria, where Kepler arranged for the printing of the new tables at his own expense.
Brahe had wanted the tables to be dedicated to his patron, the Bohemian king and Holy Roman emperor Rudolph II. But by the time of their publication in 1627, Rudolf II had died, so instead the tables were dedicated to Emperor Ferdinand II but were still named in honor of Rudolph II.
The Rudolphine Tables (Latin: Tabulae Rudolphinae) included a star catalogue and planetary tables. Most of the calculated positions were accurate to within one minute of arc. In addition, the tables were the first to include corrective factors for atmospheric refraction. In fact, the tables were so accurate that they led to the first observed transits of Mercury (in 1631) and of Venus (in 1639).
The next transit of Venus will occur over June 5-6. To learn more, visit these links.
2012 Transit of Venus, NASA/Goddard Space Flight Center: eclipse.gsfc.nasa.gov/OH/
Transit of Venus, Sun-Earth Day 2012, NASA: sunearthday.nasa.gov/transitofvenus/