History of Astronomy Notes

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

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

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

Classical Period – Famous Scientists Pythagoras (560-489 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

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

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

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

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

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.

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

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

Sir Isaac Newton (1642-1727) 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