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Islamic astronomers taking observations

Islamic astronomers taking observations

West Asian astronomy before Islam

West Asian astronomers had been world leaders in astronomy for thousands of years before the Islamic conquests in the 600s AD. In the last centuries BC, West Asian astronomers had already figured out that the earth was a ball, and that the earth went around the sun, and how big the earth was, and that the moon went around the earth. Astronomers already understood lunar and solar eclipses.

West Asian science
History of astronomy
Medieval Islamic science
All our medieval Islam articles

Did the earth go around the sun?

But there was one big problem. If the earth really went around the sun, astronomers should see parallax from the earth’s motion relative to the stars – and you can’t see it with your naked eyes. Therefore, either the earth really didn’t go around the sun, or the stars were so far away that the parallax was too small to see. But that would mean the stars were *really* far away – the nearest star would be trillions of miles away. Astronomers just couldn’t believe that the universe was that big (even though the nearest star really is about 24,800,000,000,000 miles away – almost 25 trillion miles).

What is parallax?
Who said the earth went around the sun?

Islamic astronomers, with a gold astrolabe hanging from the ceiling

Islamic astronomers, with a gold astrolabe hanging from the ceiling

Ptolemy and heliocentrism

Under Roman and Sassanian rule, scholars like Ptolemy went back to thinking that the sun and planets went around the earth. We call this idea “heliocentrism” from the Greek word “helios” for sun.

Ptolemy and Roman astronomy

Islamic and Indian astronomers

But after the Islamic conquests, astronomers began to think about this problem again. Indian astronomers like Arya Bhata about 500 AD renewed the idea that the earth spun around on its axis to make day and night. About 900 ADAl Razi continued Arya Bhata’s work to show that the sun was bigger than the earth and the moon was smaller than the earth. Just before 1100 ADAl Ghazali was able to show what caused lunar and solar eclipses again.

Who was Arya Bhata?
What did al Razi do?
How about al Ghazali?

An Islamic astrolabe (832 AD)

An Islamic astrolabe (832 AD)

Working towards telescopes

Along with these observations of the planets and the stars, Islamic scientists like Ibn Sahl in the 900s AD also improved our understanding of how lenses work. Ibn Sahl drew diagrams showing how light passing through glass or water is refracted (bent) and emerges at a different angle. In the early 1000s, Ibn al-Haytham al Basri continued this work on optics in Cairo, figuring out how this light reached your eyes. Al-Haytham’s Optics reached and influenced astronomers all the way from Europe to China.

Ibn al-Haytham

Understanding what galaxies are

In 1260 AD, another Islamic astronomer, Al Tusi, figured out that the Milky Way was made of hundreds of stars, but he thought they must be very small stars, not realizing how far away they were.

Who was al-Tusi?
What are galaxies?

Learn by doing: observe an eclipse of the moon
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Bibliography and further reading about Islamic astronomy:


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