Nur ad-Din al-Bitruji facts for kids

Nur ad-Din al-Bitruji (known in the West as Alpetragius) was an important Arab astronomer and judge from al-Andalus (modern-day Spain). He lived around the 12th century and died around 1204.

Al-Bitruji was the first astronomer to suggest a new way of understanding how planets move. His ideas were different from the old models by Ptolemy, which had been used for a long time. Al-Bitruji thought planets moved on spheres centered around the Earth. He also tried to explain why celestial bodies moved the way they did. His new system became popular in Europe during the 1200s.

A crater on the Moon is named Alpetragius in his honor.

Al-Bitruji's Life and Times

We don't know much about Al-Bitruji's early life. His name likely comes from a region in Spain called Los Pedroches, near Cordoba.

He was a student of another famous scholar named Ibn Tufail. Al-Bitruji also lived at the same time as Averroes, who was a very influential thinker.

His Big Idea About Planets

Al-Bitruji had a new theory about how planets move in space. He wanted to explain planetary motion without using complicated ideas like epicycles (small circles planets were thought to move on) or eccentrics (off-center circles).

Instead, he suggested that planets moved by combining rotations of homocentric spheres. These were spheres all centered around the Earth. This idea was a change from earlier models by scholars like Ibn Bajjah and Ibn Tufail.

However, Al-Bitruji's model wasn't as good as Ptolemy's at predicting exactly where planets would be. This was because it was hard to fit Ptolemy's detailed observations into Aristotle's simpler idea of concentric spheres.

Why Do Planets Move?

One of Al-Bitruji's most original ideas was trying to explain the physical cause of celestial motions. He combined two concepts:

• The idea of "impetus" (a kind of force that keeps things moving).
• The concept of "desire" (shawq in Arabic).

He used these ideas to explain how energy might transfer from a "first mover" (a force in the outermost sphere) to all the other spheres. This helped explain why different spheres moved at different speeds. He believed the same rules of motion applied to both Earthly things and celestial bodies, which was different from what Aristotle taught.

How His Ideas Spread

Al-Bitruji's new system became well-known across Europe in the 13th century. People debated and discussed his ideas for centuries, even up to the 1500s.

Copernicus, a famous astronomer who later proposed that the Earth orbits the Sun, even mentioned Al-Bitruji's system in his important book, De revolutionibus.

His Important Book

Al-Bitruji wrote a book called Kitāb al-Hayʾah, which means "The Book of Theoretical Astronomy" or "Cosmology." In this book, he criticized Ptolemy's famous work, the Almagest, from a physical point of view.

His book was very important in Europe between the 13th and 16th centuries. Many scholars saw it as a good alternative to Ptolemy's Almagest.

Kitāb al-Hayʾah was translated into Latin in 1217 by Michael Scot. It was later printed in Vienna in 1531. A Hebrew translation was also made in 1259 by Moses ibn Tibbon.

There is also an old paper from 1192 about tides that seems to have used some of Al-Bitruji's ideas.

See also

In Spanish: Alpetragio para niños