Geocentrism

Geocentrism is an old idea about space where Earth is at the center of everything. In this idea, the Sun, Moon, stars, and planets all move around Earth. Many ancient people, like those in Greece and Egypt, believed this.

Two main reasons made people think Earth was the center. First, the Sun seems to go around Earth once every day. The Moon and planets also seem to move around us each day, and the stars look like they are fixed on a big spinning sphere above us. Second, standing on Earth, it always feels solid and still, like we are not moving at all.

Even though some ancient thinkers, like Aristarchus, suggested that the Sun might be at the center instead, most people stuck with the Earth-centered view for a long time. It was only much later, in the 16th and 17th centuries, that scientists like Copernicus, Galileo, and Kepler showed that everything actually moves around the Sun. This new idea took time to be accepted because the old Earth-centered model worked well for making predictions about the sky. Universe Sun Moon stars planets orbit Aristotle Islamic Golden Age once per day fixed celestial sphere an axis geographical poles Ancient Greek ancient Roman medieval spherical Earth flat-Earth mythology Aristarchus of Samos heliocentric model circular Western culture Johannes Kepler elliptical Kepler's first law of planetary motion Isaac Newton Ptolemy's geocentric model astrological astronomical charts early modern Copernicus Galileo consensus

Ancient Greece

In the 6th century BC, Anaximander thought Earth was like a pillar in the middle of everything. He believed the Sun, Moon, and planets were holes in wheels around Earth, letting us see hidden fire. Around the same time, Pythagoras thought Earth was a sphere but not in the center; it moved around an unseen fire.

Later, Plato and Aristotle taught that Earth was a still sphere in the middle of the universe. They said stars and planets moved around Earth on invisible spheres. Eudoxus of Cnidus helped make these ideas more mathematical. Aristotle imagined many clear, moving spheres around Earth, holding up the stars and planets. He thought Earth was made of heavy elements that stayed in the center, while lighter elements moved away.

People believed Earth was still because the shapes of stars in the sky never seemed to change. They thought if Earth moved, we would see stars shift, but they didn’t. Also, the way the planet Venus looked stayed mostly the same, which fit better with Earth being still. Later, new ideas helped explain the movements better, but the old Earth-centered view was still widely believed.

Ancient Indian

Before around 1500, Indian astronomy focused on predicting the movements of the Sun and planets, instead of describing the whole universe. Early astronomers made different methods for inner planets like Mercury and Venus, and for outer planets like Mars, Jupiter, and Saturn. These methods were similar to a later system called the Ptolemaic system but were better at calculating where the planets would be.

By 1500, an astronomer named Nilakantha Somayaji created one method that worked for all the planets. Some Indian astronomers, like Aryabhata, thought the Earth spun, but they still believed Earth was at the center of everything.

Kerala astronomers Nilakantha Somayaji Aryabhata

Ptolemaic model

Long ago, a wise thinker named Claudius Ptolemaeus wrote about how he thought the universe worked. He believed that Earth was right in the middle of everything, like a ball in the center of a big round room. The sun, the moon, and all the stars and planets went around Earth in big circles.

Ptolemaeus used special ideas to explain how the planets moved. He thought each planet moved in a small circle called an epicycle while also going around a bigger circle called a deferent. This helped him explain why planets sometimes seemed to move backward in their paths across the sky, which we call retrograde motion. Even though his ideas were very clever, they didn’t always match exactly what we see in the sky. But for a long time, many people thought his way of understanding the universe was right.

Main articles: Maragheh observatory, Astronomy in medieval Islam, and Islamic cosmology

After Ptolemaeus wrote his ideas, people in many lands thought about them too. In places far away, thinkers used and changed his ideas. Some wondered if Earth moved instead of staying still. Others tried new ways to explain the paths of the planets without using all the same circles Ptolemaeus used.

One group of thinkers, called the Maragha school, tried very hard to make better explanations. They found ways to explain the planets’ movements that were closer to what we actually see. But even they still thought Earth was the center of everything. Much later, a new idea came that Earth wasn’t the center after all — but that’s a story for another time.

The Ptolemaic order of spheres from Earth outward is:

1. Moon
2. Mercury
3. Venus
4. Sun
5. Mars
6. Jupiter
7. Saturn
8. Fixed Stars
9. Primum Mobile ("First Moved")

Ptolemaic and rival systems

Not all Greeks agreed with the geocentric model. Some believed the Earth was one of several planets going around a central fire. Others thought the Earth turned but stayed at the center of the universe. These ideas still kept the Earth at the center.

Aristarchus of Samos wrote about a idea where the Sun was at the center, and the Earth and other planets went around it. But this idea was not popular at the time.

Copernican system

In 1543, a book by Copernicus said that the Earth and planets move around the Sun. For a long time, many people still believed the old geocentric system because the new idea did not make better predictions yet.

Tychonic system

Tycho Brahe measured where planets and stars were very well. He created a new idea where the Earth stayed in the middle. In this idea, the Sun moved around the Earth, and all the other planets moved around the Sun.

Observation by Galileo and abandonment of the Ptolemaic model

With the invention of the telescope in 1609, Galileo made observations that questioned some ideas of geocentrism. He saw moons orbiting Jupiter, showing not everything revolved around the Earth. He also saw phases of Venus that showed it orbited the Sun, supporting the idea that the Earth was not the center of everything.

Historical positions of the Roman Catholic hierarchy

The geocentric model was discussed by Galileo. Two Popes said that science and Scripture could work together. They explained that Scripture used words that people understood at the time, and it did not try to explain the universe in detail.

Gravitation

Johannes Kepler studied the careful notes made by Tycho Brahe. He used these notes to make three important rules about how planets move in 1609 and 1619. These rules helped him predict when Venus would pass in front of the Sun.

Later, Isaac Newton explained the law of universal gravitation in 1687. He showed how gravity keeps planets moving and holds the atmosphere close to Earth. His work helped prove that the Sun, not Earth, is at the center of our solar system. Many tests over time supported Newton’s ideas about gravity.

Relativity

Albert Einstein and Leopold Infeld said that we can describe nature from any point, not just ones that move smoothly. This means that saying "the Sun is still and the Earth moves" or "the Sun moves and the Earth is still" are just two ways to describe the same thing.

Relativity does not support the old idea that Earth is the center of everything. It says we could choose the Sun, the Earth, the Moon, Jupiter, or any other point as the center of our solar system, and each choice would be fine. But when we watch the planets, they move mostly in oval paths around the Sun, not the Earth. This is because the Sun is much bigger and its gravity affects the planets' paths.

The key idea from relativity is that we can predict how objects move accurately, no matter which point we start from. Choosing the Sun as the center might make calculations simpler, but it is not required. A geocentric view can be useful when we only care about things close to Earth, like the Moon or satellites.

Religious and contemporary adherence to geocentrism

See also: Geocentric creationism

The Ptolemaic model was used until the early modern age when it was replaced by the heliocentric model. Even so, some people still believe in geocentrism for religious reasons. For example, in the United States between 1870 and 1920, some members of the Lutheran Church–Missouri Synod wrote articles about it, though the church did not officially support it.

Today, some religious leaders and scholars still discuss geocentrism. For example, Robert Sungenis has written books and films about it. Some Orthodox Jewish leaders and a few Sunni scholars, like Ahmed Raza Khan Barelvi from the Indian subcontinent, also support geocentrism. Surveys show that some people in different countries still believe the Sun moves around the Earth.

Planetariums

Many planetariums can show the universe in two ways: one with Earth in the middle and one with the Sun in the middle. The Earth-in-the-middle model is still used in schools to help teach about the sky and the Moon's phases.

Ephemerides

Ephemerides are tables that show where the sun is. These tables help us learn about the sun’s position. They are useful for studying space and guiding ships and planes. They are easier to calculate if we think Earth is at the center of everything.