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Solar system: Early views

Views in the ancient Near-East

Babylon, Judea/Israel, Syria, Mesopotamia.

In early Egyptian and Mesopotamian thought the world was portrayed as a flat disk floating in the ocean. It was speculated that there were waters in the Heavens above, and waters gathered in the deep below.

This idea is found in most religious texts and religions from the ancient near-east. Some statements about this exist in the Hebrew Bible (“Old Testament”) and in the New Testament.

Here is an image taken from:


The Ancient Greeks


As far back as the Greek philosophers Pythagoras (6th century BCE) and Parmenides (5th century BCE) it was recognized that the Earth is spherical.

The Greek philosopher Aristotle proposed that the heavens were literally composed of 55 concentric, crystalline spheres.

Time period – 380 BCE

He suggested that celestial objects were attached, and rotated at different velocities, with the Earth at the center.

The following figure illustrates the ordering of the spheres to which the Sun, Moon, and visible planets were attached.

By adjusting the velocities of these concentric spheres, many features of planetary motion could be explained.

The supposed spheres moved with constant angular velocity, and the objects attached to them were always the same distance from the earth because they moved on spheres with the earth at the center.

However, the troubling observations of varying planetary brightness and retrograde motion could not be accommodated:

Below is a representation of the apparent motion of the Sun, Mercury, and Venus from the earth. Taken from the “Astronomy” article in the first edition of wikipedia:Encyclopædia Britannica (1771).

This geocentric diagram shows, from the location of the earth, the sun’s apparent annual orbit, the orbit of Mercury for 7 years, and the orbit of Venus for 8 years, after which Venus returns to almost the same apparent position in relation to the earth and sun.

James Ferguson (1710-1776), based on similar diagrams by Giovanni Cassini (1625-1712) and Dr Roger Long (1680-1770); engraved for the Encyclopaedia by Andrew Bell. – Encyclopaedia Britannica (1st Edition, 1771; facsimile reprint 1971), Volume 1, Fig. 2 of Plate XL facing page 449.



What does retrograde motion look like?

“Over the course of a single night, a planet will move from East to West across the sky, like any other celestial object near the ecliptic…. If observed from one night to the next, however, a planet appears to move from West to East against the background stars most of the time. “

“Occasionally, however, the planet’s motion will appear to reverse direction, and the planet will, for a short time, move from East to West against the background constellations. “

“This reversal is known as retrograde motion, and is illustrated in the following animation.”


Epicycles and Planetary Motion

The “solution” to these problems came in the form of a mad, but clever proposal: planets were attached, not to the concentric spheres themselves, but to circles attached to the concentric spheres.

* circles were called epicycles

* the concentric spheres to which they were attached were deferents



More Sophisticated Epicycles:
The Ptolemaic Universe

Even this was not enough to account for the detailed motion of the planets on the celestial sphere. In more sophisticated epicycle models further “refinements” were introduced:

  • In some cases, epicycles were themselves placed on epicycles, as illustrated in the adjacent figure.

  • In actual models, the center of the epicycle moved with uniform circular motion, not around the center of the deferent, but around a point that was displaced by some distance from the center of the deferent.

That ancient astronomers could convince themselves that this elaborate scheme still corresponded to “uniform circular motion” is testament to the power of three ideas that we now know to be completely wrong, but that were so ingrained in the astronomers of an earlier age that they were essentially never questioned:

  1. All motion in the heavens is uniform circular motion.

  2. The objects in the heavens are made from perfect material, and cannot change their intrinsic properties (e.g., their brightness).

  3. The Earth is at the center of the Universe.

These ideas concerning uniform circular motion and epicycles were catalogued by Ptolemy in 150 A.D. His book was called the “Almagest” (literally, “The Greatest”), and this picture of the structure of the Solar System has come to be called the “Ptolemaic Universe”.


This image is from http://www.malinc.se/math/trigonometry/geocentrismen.php

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Flash animations: Ptolemy’s models



During the Middle Ages, these ideas were incorporated into religion. The Middle Ages – medieval period – lasted roughly from the 5th to the 15th century: from the fall of the Western Roman Empire, to the Renaissance.

In this era, the writings of Socrates, Aristotle, Ptolemy and others were rediscovered by Jewish, Christian and Muslim scholars. These religious scholars were impressed with the logical, rational analysis of the world by the early Greek and Roman philosophers.

So in this era, Jewish, Christian and Muslim scholars created a synthesis of science, logic, and reason with revealed faith.  This way of thinking is called philosophical rationalism, or Scholasticism.

Some of the Christian scholastics include:

Thomas Aquinas (“Doctor Angelicus”)
Duns Scotus (“Doctor Subtilis”)
William of Ockham (“Doctor Invincibilis”)

Some of the Jewish scholastics include:

Gersonides, Levi ben Gershon

Maimonides, Moses Ben Maimon

Some of the Muslim scholastics include:

Ibn Rushd, known by his Latinized name, Averroes (“The Commentator”)

Ibn-Sīnā. Known by his Latinized name, Avicenna.

How did this affect the history of science? The Prime Mover of Aristotle’s universe became identified with God. The outermost sphere of the Prime Mover became identified with Heaven. The Greek hypothesis that the Earth was at the center of the universe was mistakenly interpreted as a proven fact. It was then reinterpreted as proof that God put Earth, and humankind, at the center of all creation.

Thus the philosophy of pagan Greek philosophers were incorporated into religious writings of Judaism, Christianity and Islam.  Over time, later religious believers began to teach that these books were infallible – so the teachings within them became a new religious dogma.

After a while, it became almost impermissible for anyone to disagree with these teachings.  Due to this belief, the progression of science slowed down for quite some time, until the scientific revolution and the enlightenment.

The scientific revolution

Medieval to modern views of the solar system

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

Understandings about the Nature of Science:  Science knowledge has a history that includes the refinement of, and changes to, theories, ideas, and beliefs over time.

Science Is a Human Endeavor:  Scientific knowledge is a result of human endeavor,
imagination, and creativity. Individuals and teams from many nations and cultures have contributed to science and to advances in engineering.

Massachusetts History and Social Science Curriculum Framework

The roots of western civilization: Ancient Israel

The roots of western civilization: Ancient Greece


Describe the purposes and functions of development of Greek institutions such as the
lyceum, the gymnasium, and the Library of Alexandria, and identify the major accomplishments of the ancient Greeks.
A. Thales (science.)  B. Pythagoras and Euclid (mathematics.)  C. Hippocrates (medicine.)  D. Socrates, Plato, and Aristotle (philosophy.)

Next Generation Science Standards

HS-ESS1 Earth’s Place in the Universe
Construct an explanation based on valid and reliable evidence obtained from a variety of sources (including students’ own investigations, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future. (HS-ESS1-2)
Apply scientific reasoning to link evidence to the claims to assess the extent to which the reasoning and data support the explanation or conclusion. (HS-ESS1-6)

Engaging in Argument from Evidence: Use appropriate and sufficient evidence and scientific reasoning to defend and critique claims and explanations about the natural and designed world(s). Arguments may also come from current scientific or historical episodes in science.

Connections to Nature of Science:
Science Models, Laws, Mechanisms, and Theories Explain Natural Phenomena.
A scientific theory is a substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment, and the science community validates each theory before it is accepted. If new evidence is discovered that the theory does not accommodate, then the theory is generally modified in light of this new evidence. (HS-ESS1-2),(HS-ESS1-6)

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