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Solar system: Early views

Views in the ancient Near-East

Circa 3000 BCE to 2000 BCE

Worksheets – Solar system part 1.docx

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.


The Ancient Greeks

Text from this section excerpted from Astronomy 161 The Solar System, Dept. Physics & Astronomy, Univ of Tennessee. Astr 161 – Aristotle (website now defunct)

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 Ἀριστοτέλης (384-322 BCE) proposed that the heavens were composed of 55 concentric, crystalline spheres.

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 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.



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



This section has been excerpted & adapted from Astronomy 123 Cosmology, James Schombert, Univ. of Oregon. Astronomy 123, Lecture 2

Aristarchus was the first to propose a Sun centered cosmology.

one of the primary objections to the heliocentric model is that the stars display no parallax (the apparent shift of nearby stars on the sky due to the Earth’s motion around the Sun).

However, Aristarchus believed that the stars were very distant and, thus, display parallax’s that are too small to be seen with the eye.

In fact, parallax of stars would not by measured until 1838.

The Sun is like the fixed stars, states Aristarchus, unmoving on a sphere with the Sun at its center. For Aristarchus it was absurd that the “Hearth” of the sky, the Sun, should move and eclipses are easy to explain by the motion of the Moon around the Earth.

The problems, at the time, for accepting this heliocentric theory were:

* It was impossible for people back then to imagine the motion of the Earth orbiting the Sun without being able to `feel’ it. Since no motion was felt they used “common sense” to reason that the Earth isn’t moving.

* If the Earth undergoes a circular orbit then the nearby stars would show a parallax. A parallax is an apparent shift in the position of nearby stars relative to distant stars. No parallax was observed at that time, so they correctly understood that:

(A) either the parallax must be very, very small (which it is!) meaning that the stars are vastly far away (which they are!)

or (B) the Earth isn’t orbiting the Sun at all. They chose (B.)
Given the lack of observational data at the time, it seemed a reasonable choice. (But they were incorrect.)

* The geocentric ideas seem more natural to people back then. Earth at the center of the Universe is a very ego-centric idea, and has an aesthetic appeal.

What is parallax?

This images shows the Sun at the bottom. and the orbit of the Earth as a circle around it. Earth is Winter is at position 1, and Earth during summer is at position 2.  Some stars (above) are far away.

Imagine being on the Earth and looking up at some of the closer stars. During Winter (1) we see this star as if it is at a certain position (B). Yet during summer (2) we look at the same star, and it appears to be in a different position (A).

The star doesn’t move during this time; the apparent change in position is an optical illusion of sorts. This apparent change of position due to the motion of the observer is called parallax.

Solar System in the time of Ptolemy

Claudius Ptolemy (Κλαύδιος Πτολεμαῖος) (100 – 170 CE) was a Macedonian Hellenist mathematician, astronomer, geographer and astrologer who wrote several scientific treatises.

This next section has been excerpted from Ptolemy to the Rescue? Astronomy 121

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

– – – – – –


Views during the Middle Ages

During the middle ages these speculative-science ideas about the solar system were incorporated into religion. For many centuries afterward, many people were taught that these ideas were religious beliefs that could not questioned.

The Middle Ages – medieval period – lasted roughly from the 5th to the 15th century. They range 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 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. That was then interpreted 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.

ESS1. Earth’s Place in the Universe

8.MS-ESS1-1b. Develop and use a model of the Earth-Sun system to explain the cyclical pattern of seasons, which includes Earth’s tilt and differential intensity of sunlight on different areas of Earth across the year.

8.MS-ESS1-2. Explain the role of gravity in ocean tides, the orbital motions of planets, their moons, and asteroids in the solar system.

ESS1.B Earth and the solar system – The solar system contains many varied objects held together by gravity. Solar system models explain and predict eclipses, lunar phases, and seasons.

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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