Historical Astronomers in Context

Figure 1. Portrait of Johannes Kepler.

Johannes Kepler (December 27th, 1571 – November 15, 1630) helped the world of astronomy and the general field of sciences in several key ways. First, Kepler utilized Tycho Brahe’s data concerning the position of stars and planets in the sky during different days in the year to determine that the orbit of Mars was elliptical rather than circular. Mars was specifically selected as predictions concerning its position in the sky produced the most errors. Kepler’s discoveries eventually led him to establish Kepler’s Laws of Planetary Motion. The three involved laws are as follows:

Law #1: Planets orbit the Sun in an elliptical path with the Sun residing at the focus.

Law #2: The radius vector (which is defined as the distance from an orbiting object to the source of gravity) represents equivalent areas in equal time periods. In other words, for orbiting objects to attain/sweep across an area at a constant rate, the objects increase in speed when the velocity vector is small and decreases in speed when the velocity vector is large.

Law #3: P² = a³, where P is the period of the orbit, and a is the semi-major axis of the orbit.

Such laws led to Kepler being named “the father of celestial mechanics”. Additionally, Kepler was the first person to explain that the ocean tides are created by the Moon. Interestingly, Galileo did not approve of this explanation. Lastly, Kepler was the first to determine that the Sun rotates about its axis.

Historical Events:

(1606) The first permanent English colony of Jamestown, Virginia is established. This is also the time in which John Smith (leader of the Virginia Colony) was rescued from execution by Pocahontas.

(1618) The Thirty Years’ War begins. This war involved protestants fighting against catholic oppression (with most of the war occurring in the Holy Roman Empire).

Historical Figure:

Sir Francis Drake: Birth Date – c. 1540

Date of Death – January 28, 1596

Sir Drake was the first person to circumnavigate the Earth (or sail around the Earth) within one single expedition. This was a key action that initiated conflict between the English and Spanish over land on the western coast of North and South America.

Reflection:

Analyzing world events alongside the work in which Kepler performed really places into perspective how societies were advancing in the understanding of the sciences and in technology while the world was in constant conflict. Not only did these astronomers have to go against the Church (and risk their lives for it), but they had to compete with conflicting observations (just as Galileo disagreed with Kepler concerning the cause of the tides of the oceans). Lastly, even though the technology was advancing, I find it highly impressive that Kepler (and the other astronomers within this assignment) managed to collect highly accurate data and produce precise predictions of the positioning of planets, stars, etc. at a given time. That takes a great deal of patience and dedication.

astro2110, HW2, Kepler