1. History of Astronomy Notes

2. Four Periods of Astronomy
Prehistoric – before 500 BC
Classical – 500 BC to 1400 AD
Renaissance – 1400 to 1650
Modern – 1650 to present

3. Prehistoric Period
People observed daily and seasonal motions of sun, moon & stars
Used stellar motion to keep time and determine distance
Able to predict events like sunrise and sunset
Developed constellations
Stonehenge
Built by ancient Britons on Salisbury Plains
Marks seasonal rising & setting points of the sun
World’s first clock and first observatory

6. Classical Period
Scientists & Philosophers began to make measurements of the heavens.
Constructed models to account for motions of heavenly bodies – with the help of geometry
First ‘real’ scientists
Ancient Greeks were first to try to explain the workings of the heavens using models and observations
Limited to naked-eye observations.
Numerous famous scientists from this period

7. Classical Period – Famous Scientists
Pythagoras ( BC)
First to teach that the Earth was spherical
Believed that the sphere was a perfect shape
Gods would have used this shape to create Earth
Aristotle (384 – 322 BC)
Helped to prove Earth was a sphere
Proved based on observations of lunar eclipses

8. Classical Period – Famous Scientists
Eratosthenes (276 – 195 BC)
Made first measurements of Earth’s size
Obtained a value of 25,000 miles circumference
True circumference – 24,901.55
Ptolemy
Researched planetary motions
Thought that each planet moved on one small circle, which moved on a larger one – like a frisbee spinning on a bicycle wheel – called epicycles
Idea survived until the 1500’s

9. Reniassance Period Models re-assessed
New models that took into account data-based observations
Invention of telescope
Heliocentric Model introduced

10. Copernicus (1743-1543) Developed & taught Heliocentric Model
Described retrograde motion of the planets
Calculated distance to planets
Ideas weren’t accepted by the Catholic Church – forced to stop teaching Heliocentric views

12. Tycho Brahe (1546-1601) Born into nobility (Duke)
Believed God placed planets in heavens to be used as signs to mankind of events on Earth
Built tools to measure planetary motions
In his model, all planets except Earth went around the Sun – the Sun circled the Earth
Last great astronomer to believe that Earth was center of universe

14. Johannes Kepler (1571-1630) Brahe’s assistant
Used precise info to show that Mars moved in an elliptical orbit
Developed 3 Laws of Planetary Motion:
Planets move in elliptical orbits
Planet’s speed always covers equal areas in equal time
p2 = a3 (p is the period of orbit and a is the longest distance from the Sun to the planet)
Kepler is credited with coming up with the word ‘satellite’ when he saw the moons of Jupiter.

16. Galileo Galilei (1564-1642) Invented the telescope
Believed & taught Heliocentric theory
Developed the scientific method
Discovered craters & mountains on moon, sunspots, 4 moons of Jupiter, Saturn’s rings, phases of Venus
Brought before the Holy Roman Inquisition and ordered to stop teaching his Heliocentric view
Finally stopped teaching his views after being threatened with death
Spent last 13 years of his life under house arrest

18. Modern Period
Scientists began to search for physical laws (like gravity)
Major advanced in technology – optics, electronics, computers
Better mathematic techniques
Astrophysics – uses physical laws to understand the structure and workings of heavenly bodies

19. Sir Isaac Newton ( )
Greatest scientist of all time – math, physics, astronomy
Pioneered studies in motion, optics, and gravity
Religious man – wrote on theology as well as scientific matters
3 Laws of Motion