Geol 1420 Chapter 2.2

Based on Egyptian and Babylonian foundations: - Extensive celestial records - Constellations - Measurement systems such as the 360-degree circle - Ecliptic plane
Egyptians and Babylonians referred to planets as "the wanderers"; they believed that the stars were fixed and that the planets were special stars that could wander.
The term "planet" derives from the Greek word "planetes," meaning "wanderer."

Developed the first known model of the universe which was not based on supernatural beliefs.
Proposed a flat disk universe floating on an infinite ocean.

Classified motion into three types: - Natural motion: - Objects move toward their "natural place" without external forces (e.g., a stone falling to the ground). - Voluntary motion: - Motion resulting from a choice (e.g., animals running). - Forced motion: - Motion caused by an external force pushing or pulling an object; motion ceases once the force is removed.
Stated that objects at rest remain at rest unless acted upon by a force, and objects in motion slow down unless a force is applied continuously.

The Greeks made significant progress in the fields of mathematics and geometry, applying these concepts to the natural world.

Key postulates proposed by Euclid include: - Given two distinct points (A & B), there exists a unique line passing through them (denoted as l). - A line segment can be extended on both ends to form a full line. - A circle can be drawn with any center and any radius.
Additional postulates include: - All right angles are congruent to one another. - For any line l and a point P not on l, there exists a unique line m through P that is parallel to l.

First individual to propose a Sun-centered universe where Earth revolves around the Sun.
Utilized geometry and observations of lunar eclipses to estimate the relative sizes and distances of the Earth, Moon, and Sun.
Concluded that the Sun is significantly larger and farther from Earth.

Successfully computed the circumference of the Earth using geometric principles and the shadow of a stick measured in two cities in Egypt.

Earth is positioned at the center of the universe, a belief strongly supported by Aristotle.
Aristotle theorized that celestial bodies (Sun, Moon, planets, fixed stars) revolved around Earth.

Two main observations supporting the geocentric perspective include: - The apparent daily revolution of the Sun, Moon, and stars around Earth. - The perception that Earth is stationary for Earthbound observers (it appears solid, stable, and unmoving).

Geocentric models struggled to explain retrograde motion, which is the apparent backward motion of celestial objects as observed from Earth.
Retrograde motion is actually an illusion caused by the differing orbital speeds and distances of the planets relative to Earth.

To address the issue of retrograde motion within a geocentric framework, Ptolemy proposed that planets travel along smaller circles known as epicycles, the centers of which move around a larger circle (the deferent) that encircles Earth.
This framework is referred to as the Ptolemaic epicyclic model.

A philosophical principle stating that "Entities should not be multiplied beyond necessity" as attributed to William of Ockham (c. 1285-1349).
Albert Einstein paraphrased it as "Theories should be as simple as possible, but no simpler."
In essence, the natural world tends to be simple, and our theoretical constructs should reflect that simplicity.
The Ptolemaic system was criticized for its complexity and lack of elegance due to the convoluted nature of planetary orbits.

The Heliocentric model posits that the Sun is at the center of the Solar System, a model formulated by Copernicus, a Polish mathematician and astronomer.
In this model, the planets orbit the Sun, while the Moon orbits Earth. The Sun and stars are considered motionless.

Superior planets (orbiting farther from the Sun than Earth): - Mars, Jupiter, Saturn
Inferior planets (orbiting closer to the Sun than Earth): - Mercury, Venus
Describes the positions of planets through terms such as: - Inferior and superior conjunction - Opposition - Greatest elongation

The heliocentric model accounts for retrograde motion as a result of Earth overtaking slower-moving outer planets in their respective orbits.
Although not completely correct, this model provided a solid foundation for future advancements in astronomical understanding and research.

Earth is deemed the motionless center of the universe, surrounded by Sun, Moon, planets, and fixed stars, which revolve around it.
Planets are theorized to orbit in uniform circular patterns, utilizing the complex motion of epicycles and deferents to explain retrograde motions.

The Sun occupies the center of the universe while remaining static, with the stars also presumed stationary.
In this model, planets perform uniform circular motion modified by epicycles, with Mercury closest to the Sun followed by Venus, Earth, Mars, Jupiter, and Saturn.
Retrograde motion is attributed to Earth’s overtaking of slower-moving outer planets.