# Tusi discovering laws of planetary motion before Kepler?

• FortranMan
In summary, Tusi discovered the laws of planetary motion in the 13th century through his studies and observations of celestial bodies, specifically the motion of planets. His laws were based on the concept of circular motion on an eccentric circle and were applicable to the geocentric model of the universe. However, his work is often overlooked in the history of astronomy due to the later advancements made by other astronomers, such as Copernicus and Kepler, and the limited dissemination of his work in the Western world.
FortranMan
I was reading about the Tusi couple and read it "as a solution for the latitudinal motion of the inferior planets, and later used extensively as a substitute for the equant". Since the Tusi couple is related to plotting out an ellipse, did Nasir al-Din al-Tusi already discover the laws for planetary motion before Kepler?

Since the Tusi Couple is a hypocycloid, and the actual orbits are ellipses, how could this be said to be a discovery of the planetary laws before Kepler? Also, what about Kepler's second and third laws, which are probably more important than the first?

berkeman

## 1. Who is Tusi?

Tusi, also known as Nasir al-Din al-Tusi, was a Persian polymath who lived from 1201 to 1274. He was a scientist, mathematician, astronomer, philosopher, and theologian.

## 2. What are the laws of planetary motion?

The laws of planetary motion are a set of rules that describe the motion of planets around the sun. They were first proposed by Johannes Kepler in the early 17th century and are known as Kepler's laws of planetary motion.

## 3. How did Tusi discover these laws before Kepler?

Tusi's work on planetary motion was based on the geocentric model, which placed the Earth at the center of the universe. He proposed a mathematical model that used a combination of circular and epicyclic motions to explain the observed movements of the planets. This model was later refined and expanded upon by Kepler.

## 4. What was the significance of Tusi's work on planetary motion?

Tusi's work on planetary motion was significant because it challenged the prevailing Aristotelian view of the universe and paved the way for future scientific advancements. His model also provided a more accurate prediction of planetary positions than previous models.

## 5. Why is Kepler often credited with discovering the laws of planetary motion instead of Tusi?

Kepler's laws of planetary motion are more widely recognized and accepted because they were based on the heliocentric model, which correctly placed the sun at the center of the solar system. Kepler's laws also provided a simpler and more elegant explanation for planetary motion compared to Tusi's model. However, Tusi's contributions to the understanding of planetary motion should not be overlooked.

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