The History of Astronomy
The History of Astronomy Earliest astronomical record: a lunar calendar etched on bone from 6500 B.C. Uganda. Also we find early groups noted the Sun, Moon, Mercury, Venus, Earth, Mars and Jupiter
Egyptians felt certain alignments of the stars and planets caused the Nile to flood Pyramids aligned (N S E W) Pyramid shafts align with specific constellations believed to make an early sun dials.
British Isles
Stonehenge (3100 BC - 1500 BC) is aligned with the movements of celestial objects.
The Chinese developed a working calendar and kept careful track of comets, eclipses and sun spots. Early Chinese Star Chart
Chinese Oracle bones contain records of novae and comets.
The Mayan accurately predict solar and lunar eclipses. developed a very accurate calendar, later adopted by the Aztecs. This structure, called the Caracol, at Chitzen Itza may have been used as a Venus Observatory Dresden Codex The Caracol Aztec Calendar
Ancient Greeks By 500 BC, the Greeks had constructed a model that describes the motions of the sky. Geocentric model Spherical Earth at the center of the universe Sun, Moon, and planets surrounded us on perfect spheres.
EARLY GREEK ASTRONOMY Shape of Earth (circa 400 BC)
EARLY GREEK ASTRONOMY Shape of Earth (circa 400 BC) Size of Earth (Erastothenes circa 200 BC)
EARLY GREEK ASTRONOMY Shape of Earth (circa 400 BC) Size of Earth (Erastothenes circa 200 BC) Distance to the Sun
Assumptions of Early Models Geocentric - Earth in the middle Everything orbits the Earth Stars are located on the Celestial Sphere Everything moves in uniform circular motions
Aristotle ~350 BC Earth at the center of the Universe Earth was round due to gravity All heavy things sank, thus the stars and planets had to be lighter than the air.
Ptolemy 85-165 Earth was at the center of the Solar System - Geocentric Model Used epicycles to explain retrograde motion.
deferent epicycle Center Mars Earth Equant
Nicolaus Copernicus (1473-1543) Heliocentric system! Explains phases of Moon Retrograde motion Not very accurate
Tycho Brahe (1546-1601) Observations of comet Observation of supernova far away Naked eye observations of planets Best observations of planetary positions
Johannes Kepler (1571-1630) Worked for Brahe Took data after his death Spent years figuring out the motions of the planets Came up with Three Laws of Planetary Motion
Ellipses Kepler s 1st law: All planets orbit the Sun on an ellipse, with the sun at one focus.
Kepler s 2nd Law As a planet moves through its orbit, it sweeps out equal areas in equal times. Planets move: Fast at perihelion Slow at aphelion
Kepler s 3rd law More distant planets orbit the Sun at slower speeds than closer ones. Works for asteroids, comets, and everything orbiting the Sun! Period 2 Semi - major axis Constant 3
Galileo Galilei (1564-1642) Knew of Copernicus & Kepler s work Used a telescope to look at the sky
The Moon was an imperfect object Venus has phases
Jupiter has objects around it Saturn is imperfect The Sun is imperfect
Cassini 1625-1712 Saturn's Rings are split into two parts, "Cassini Division". Jupiter s Great Red Spot Observed differential rotation in gas planets
Isaac Newton (1642-1727) The ultimate nerd Able to explain Kepler s laws The Three Laws of Motion
1. Law of Inertia - Objects do whatever they are currently doing unless something messes around with them.
2. Force defined F=force m=mass F=ma a=acceleration (change in motion)
3. For every action there is an equal and opposite reaction.
Edmond Halley 1656-1742 predicted a comet's return - every 76 years.
William Herschel 1738-1822 discovered the planet Uranus
Christian Doppler 1803-1853 Theorized that waves from a moving source would be compressed or expanded. Doppler Effect
Albert Einstein 1879-1955 Einstein presented his specific theory of relativity E=mc 2 Light can bend Time slows as you near the speed of light
Edwin Hubble 1889-1953 expanding universe theory.
Gerald Kuiper 1905-1973 belt of comet-like debris at the edge of our solar system. Kuiper Belt
Carl Sagan 1934-1996 search for extraterrestrial intelligence.
Stephen Hawking 1942-Present study of black holes