What did alhazen think about the solar system?

Alhazen’s View of the Cosmos: More Than Just Geocentrism

Ever heard of Alhazen? Probably not, unless you’re deep into the history of science. But trust me, this guy was a total rock star back in the Islamic Golden Age. Born in what’s now Iraq around 965 CE, and later hanging his hat in Egypt until his death around 1040 CE, Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham—that’s Alhazen to his friends—was a true polymath. They even called him “Ptolemaeus Secundus,” or Ptolemy the Second, which is like saying he was the next big thing in astronomy i. And for good reason!

Now, here’s the thing: despite his brilliance, Alhazen’s view of the solar system might seem a bit… outdated to us today. He lived in a time when everyone “knew” the Earth was the center of the universe—the geocentric model, you know? Think Ptolemy and his whole Earth-centered cosmos. That was the prevailing wisdom i.

But don’t think Alhazen just blindly followed the crowd. He was way too sharp for that. In fact, he took Ptolemy to task in his book “Doubts Concerning Ptolemy.” He wasn’t afraid to point out inconsistencies in Ptolemy’s “Almagest,” “Planetary Hypotheses,” and even his work on “Optics.” Alhazen basically said, “Hold on a minute, these mathematical tricks you’re using—the equant, the epicycles—they don’t quite add up.” He felt Ptolemy hadn’t really nailed the “true configuration” of the planets, and Alhazen aimed to make the model better, not throw it out completely i.

His most important astronomical work, “On the Configuration of the World,” is where he really tried to bridge the gap between the math and the real world i. He wanted to explain how these abstract mathematical models could actually make sense physically. Think of it as trying to translate complex equations into something you could actually visualize.

In another work, “Model of the Motions of Each of the Seven Planets,” Alhazen sticks with the geocentric idea but ditches Ptolemy’s equant i. He dove deep into the daily movements of the planets we can see, plus the Sun and Moon. He developed a system—”celestial kinematics”—to explain their movements using circles and arcs on a celestial sphere. He figured Mars, Jupiter, and Saturn had pretty stable orbits, but he wasn’t so sure about Mercury and Venus, noticing they wobbled a bit i.

And get this: Alhazen wasn’t just about staring at the stars. He was also thinking about the atmosphere. He figured out why we have twilight, calculating the angle of the Sun below the horizon when it starts and ends. From that, he even estimated the height of Earth’s atmosphere i! He knew the Moon shined because it reflected sunlight, and he even realized the stuff in space wasn’t as dense as our air i.

What really set Alhazen apart was his commitment to actually looking at things and questioning everything. He was all about observation and experimental data. To him, that was the real source of knowledge. He wasn’t afraid to challenge the big names or the accepted theories. In my book, that makes him a true pioneer of the scientific method i.

So, yeah, Alhazen’s view of the solar system was geocentric. But he wasn’t just a parrot. He was a critical thinker, constantly questioning and refining the models of his time. And that’s why, even though his cosmology is outdated, his contributions to science still resonate today. He wasn’t just looking at the stars; he was showing us how to look at the world.