ANCIENT ASTRONOMY AND MODERN ASTRONOMY

ANCIENT ASTRONOMY AND MODERN ASTRONOMY

Men of Science and Their Models of Earth

• Rate Your Knowledge Scale:

  • 4: Clear understanding and can explain.

  • 3: Some knowledge, not very clear.

  • 2: Heard of it, don't know much.

  • 1: Never heard of it.

• Key Scientists:

  • Plato

  • Eudoxus of Cnidus

  • Aristotle

  • Aristarhcus of Samos

  • Ptolemy

  • Nicolaus Copernicus

  • Tycho Brahe

  • Galileo Galilei

  • Johannes Kepler

EARLY THEORIES ABOUT THE UNIVERSE

• Cosmogony:

  • Scientific study of the origin and evolution of the universe.

• Astronomy Definition:

  • Study of planetary motions and relative positions of celestial bodies.

• Calendar Development:

  • Early civilizations used astronomy to create calendars.

• Oldest Known Lunar Eclipse:

  • Recorded in Mesopotamia around 2000 BCE.

• Anaximenes’ Model (560 BCE):

  • Proposed a celestial sphere with stars as fixed points.

EARLY THEORIES ABOUT THE UNIVERSE (CONTINUED)

• Celestial Sphere Concept:

  • Imaginary sphere with Earth at its center.

EARTH’S MOTION

• Types of Motion:

  • Diurnal Motion:

    • Apparent daily motion of celestial sphere from east to west.

  • Annual Motion:

    • Apparent change in star locations relative to the sun.

  • Precession of Equinoxes:

    • Gradual shift in Earth’s axis orientation over time.

• Historical Note:

  • Discovered by Hipparchus, a Greek astronomer.

DEVELOPMENT IN ANCIENT ASTRONOMY

• Greek Influence (600 BCE - 400 CE):

  • Emphasized geometric and schematic methods.

  • Contrast with numerological approaches of earlier civilizations.

NOTABLE GREEK ASTRONOMERS

Plato (428-348 BCE)

• Background:

  • Philosopher and mathematician; student of Socrates.

• Beliefs:

  • Universe is perfect and unchanging; stars are divine.

Eudoxus of Cnidus (390-337 BCE)

• Contributions:

  • First to apply mathematics to astronomy precisely.

  • Developed a geocentric model with interconnected spheres.

Aristotle (384-322 BCE)

• Background:

  • Student of Plato; teacher of Alexander the Great.

• Model:

  • Proposed 55 concentric spheres around a stationary Earth.

  • Introduced celestial and terrestrial motion concepts.

ARISTARCHUS OF SAMOS

• Key Contributions:

  • Proposed a heliocentric model with the sun at the center.

  • Worked on measuring sizes and distances of celestial bodies.

PTOLEMY (100-170 CE)

• Ptolemaic System:

  • Earth-centered universe model; last of classic astronomers.

  • Planets move in circles (epicycles) around a stationary Earth.

MODERN ASTRONOMY

• Characteristics:

  • Quantitative observations.

  • Theories based on logical and mathematical concepts, confirmed through direct observation.

Nicolaus Copernicus (1473-1543)

• Heliocentric System:

  • Proposed Sun at the center of the universe; Earth as one of many planets.

TYCHO BRAHE (1546-1601)

• Contributions:

  • Known for precise measurements of celestial bodies.

GALILEO GALILEI (1564-1642)

• Discoveries:

  • Developed an advanced telescope; observations of celestial bodies including moons of Jupiter and the phases of Venus.

JOHANNES KEPLER (1571-1630)

• Kepler’s Laws of Planetary Motion:

  • Law of Ellipses: Orbits are elliptical with the sun at one focus.

  • Law of Equal Areas: Planets sweep out equal areas in equal time intervals.

  • Law of Harmonies: Relationship between the square of the orbital period and the cube of the orbital radius.