Astronomy throughout history

The night sky, a source of great wonder. Marvelous stories, and plenty of practical use. More than 3,000 years ago, the ancient Babylonians started the phases of the moon, using them to develop a lunar calendar. They made systematic observations and uncovered the regular patterns of the moon as it changed appearance. That mysterious light in the sky became a predictable and useful tool for telling the time.

Throughout the world, scholars were fascinated by the object - a light in the sky. Ancient Greeks wanted to understand how the sun, the moon, and the stars moved across the sky. Aristotle was one of the greatest thinkers at the time, but no matter how long he thought about it, there was one thing he never questioned. He kept Earth at the center, and those other objects revolving around it. In Aristotle's model of the world, Earth was surrounded by layers of crystal spheres.

Each one contained a celestial body like a planet, the moon, or the sun, and they moved harmoniously around the Earth in perfect circles. As Aristotle's world model placed Earth at the center, it was an Earth-centered, or geocentric, model. Looking at the sky from Earth, the geocentric model seems reasonable, and people kept believing Aristotle. Then came a Roman astronomer, Ptolemy. He noticed something odd about the movement of the stars in the sky.

At times, some of the planets seemed to be moving backwards before continuing their pathway across the sky. What if the planets were not revolving in perfect circles, he thought. Ptolemy kept the geocentric model with Earth at the center, but he introduced an elaborate mathematical model where the planets followed spiral rather than circular paths. Ptolemy was not the only astronomer who questioned Aristotle. The great astronomer, Aryabhata, lived in India.

He came up with a challenging idea that Earth is not at all stationary, but rotating on it's own axis. Maybe he suspected the Earth was also rotating around sun. 500 years later, astronomers in Persia made an observation supporting Aryabhata's ideas and expanded them. One of them, al-Khujandi, built an observatory in Tehran. There, he managed to measure the tilt of Earth in relation to the sun with impressive precision.

Bit by bit, astronomers mapped the movements and position of Earth in space. A few hundred years later, Polish astronomer, Nicolaus Copernicus, picked up the almost forgotten idea that Earth revolves around the sun. Copernicus's great contribution came from connecting this to Ptolemy's model. By placing the sun at the center, Copernicus's model could make much more accurate predictions for the planets' movements without having to calculate the complicated spiraling movements suggested by Ptolemy. Copernicus's ability to explain observations in the sky with simple mathematical calculations was a breakthough of the world model with the sun in the center - the heliocentric model.

At first, the church accepted this heliocentric model. But after Copernicus's death, religious leaders began to see his ideas as blasphemous and dangerous. Books written by Copernicus were banned for the next 200 years. Despite this, Italian astronomer Galileo Galilei learned about Copernicus's work and made observations in support of it. Galileo studied the phases of the moon and the changing positions of Mercury and Venus.

One day he noticed at least four moons are orbiting Jupiter. If moons are orbiting Jupiter, it means that not everything in the universe revolves around Earth. This strengthened Galileo's view of the heliocentric world model, but it didn't make the church happy. Galileo tried to defend his views but was eventually forced to publicly renounce his theory, and he was placed under house arrest. But that didn't stop the scientific progress.

Over time, astronomers around the world discovered more evidence in support of the heliocentric model and developed it further. Eventually, the understood that even the sun is not in the center of the universe. Even the sun is a moving part of the galaxy, which is also moving through space. All the things we know today about the universe have been put together over centuries. Astronomers from around the world have added their insights and inspired their followers to keep making new observations and calculations.

Every day, astronomers make new observations and calculations expanding and challenging current theories.