History of Astronomy Lets go back way back

History of Astronomy

Let’s go back… way back

The early guys (3000 years ago) • Before the invention of telescopes, humans had to depend on the evidence from their eyes to get a sense of the universe • What do you think they saw?

The early guys (3000 years ago) • 1200 BCE • Ancient Chinese astronomers had worked out a yearly calendar to include exactly 365¼ days • 500 BCE • The Babylonians worked on a calendar based on the phases of the Moon • Created a sundial… based on the Sun… to keep track of the passing hours of a day

The early guys • 600 BCE – 400 AD • Greek astronomers put special emphasis on the use of mathematics • Tried to figure out the distance from the Earth to the Sun and to the Moon • Earth was the centre of the universe • The Sun, Moon and stars moved around the Earth

The early guys: what they saw • Five of these objects appeared to “wander” through the constellations. These objects were considered to be special stars, which they called planets.

Aristotle (384 -322 BCE) • Knew the Sun was further than the moon • Because the moon occasionally passed between the Earth and the Sun • Determined that the Earth was a sphere 1. The Earth casts a round shadow during an eclipse • Only spheres cast round shadows • Could it be a disk? 2. Travelers that head south are able to see different stars than those who are in the north

The Geocentric Model • Geo = Earth Centric = Centered • First described by Aristotle • All celestial bodies seem to move across the sky from East to West • Earth must be at the centre, with everything moving around it

parallax

parallax • We see this ALL the time… we just didn’t know it had a fancy scientific name • Have you watched the house way off in the distance move very slowly while the tall grass in the ditch zips by when in a car? • This is called parallax… • When moving, objects that are in the distance move less than objects that are closer to us • In short… even those with the best vision could not see a shift in nearby stars as the Earth moved along

parallax • This meant either • The Earth was not moving • Or, the stars were tremendously far away • A massive universe was a hard thing to imagine • So they concluded that the Earth did not move

Aristarchus (310 -230 BCE) “Air-a-star-cus” • Proposed Earth revolves around the Sun • It was said he should be charged with lack of respect for God • Even Aristotle rejected his idea • Obtained values for the distance between the Sun and Earth

Aristarchu. S’ CALCULATIONS • Began with: • During a half moon, the moon forms a right triangle with the Sun and Earth • What would you do to solve?

Aristarchu. S’ CALCULATIONS • He also used a lunar eclipse and triangle proportions

Eratosthenes (200 BCE) “Air-a-toss-then-knees” • Estimated Earth’s diameter using geometry • All based on the sun’s rays and parallel lines (those that took Grade 10 Essentials math should recognize this)

Eratosthenes (200 BCE) • Depending on which measurement he was using • He was either 20% too large • Or, he was within 1% of the actual value

Ptolemy (100 -200 AD) “tolemy” • Determined the positions of about 1, 000 bright stars. • Summarized the geocentric model of the universe, which stated that the Earth is motionless and everything revolves around it.

The birth of modern astronomy about 1500 years later…

The Heliocentric Model • Helio = Sun Centric = Centred

Nicholas Copernicus (1473 -1543) • Devises a new model • The Earth is a planet and all planets circle the sun • Only the moon orbits the Earth

Nicholas Copernicus (1473 -1543) • His ideas were not widely accepted until a century after his death • The objections • We would feel the Earth moving • Apparent motion – do you feel a train moving? • The Earth would be torn apart at high speeds • Wouldn’t all of the other celestial bodies be as well since we consider them to be moving?

Tycho Brahe (1546 -1601) • Observed, what we now know to be, an exploding star • Made continuous records of the positions of the Sun, Moon and planets for almost 20 years • Very precise • Found a young mathematician to assist him in analyzing his planetary data • Johannes Kepler

Galileo Galilei (1564 -1642) • He’s the guy that studied motion • A ball should keep moving if you roll it on the ground… but something stops it • In 1590 he adopted the heliocentric model • The telescope was invented in 1608 and Galileo wanted one, so he made his own

Galileo Galilei (1564 -1642) • In 1609 Galileo Galilei turned the newly invented telescope up and was the first to see (however dimly) • Mountains on the moon • Saturn’s rings • Four sparks of light orbiting the planet Jupiter

Galileo Galilei (1564 -1642) • Not everything moved around the Earth • Jupiter’s moons moved around Jupiter • Jupiter was known to be in motion, but yet it was also the centre of another object in motion • The moon’s could keep up with Jupiter • Our moon could keep up with a moving Earth! • He was condemned by the church and his books were on the Church’s forbidden list until 1836 • Only in 1992 did the Catholic Church admit that they were in error for censoring Galileo’s ideas

Galileo’s battle for the heavens • DVD

Johannes kepler (1571 -1630) • Assistant to Tycho • Tycho was reluctant to provide Kepler with too much material at one time in fear he would steal the glory if he discovered a pattern • Once Tycho died Kepler had access to all the documents • Studied them for 20 years

Johannes Kepler (1571 -1630) • Developed three laws • We will go through two of them

Johannes kepler (1571 -1630) Law of Ellipses 1. Each planet moves about the Sun in an orbit that is an ellipse, with the Sun at one focus of the ellipse

Johannes kepler (1571 -1630) Law of Equal Areas 1. An imaginary line drawn from the centre of the sun to the centre of the planet will sweep out equal areas in equal intervals of time

Johannes kepler (1571 -1630) • Kepler's Laws Visualized

Isaac newton (1643 -1727) • The guy that ‘discovered’ gravity • Falling apple • Invented calculus • Discovered that sunlight was made of different colours ROY G BIV

Isaac newton (1643 -1727) • Three Laws of Motion… of the Universe 1. An object at rest stays at rest and an object in motion stays in motion unless an unbalanced force acts on it 2. The acceleration of an object produced by a force is proportional to the force and inversely proportional to the mass of the object In other words… small objects when hit go fast 3. For every action, there is an equal and opposite reaction

Isaac newton (1643 -1727) • Showed that Kepler’s laws were special cases of his own three laws • All objects in the universe had mass and this meant that planets moved in ellipses because of gravity • Universal Law of Gravity • As two bodies move farther away from each other, the gravitational force between them decreases • If objects are twice as far apart, the force of gravity is only a forth as strong

Albert Einstein (1879 -1955) • Disliked school and preferred to study at home • Didn’t complete secondary school • Failed the entrance exam to Zurich Polytechnic • Went back to secondary school and then got in to Zurich Polytechnic • Graduated as a high school teacher of math and physics and later became a professor

Albert Einstein (1879 -1955) • E=mc 2 • A small amount of mass creates a large amount of energy, if it can be converted • The stars • Two atoms fuse (Hydrogen fuse into Helium) and it creates a lot of energy • Nuclear fusion • Theory of Relativity

Edwin Hubble (1889 -1953) • Realized that the Milky Way is just one of the millions of galaxies and discovered the expansion of the Universe. • Hubble Space Telescope is named after him

Stephen hawking (1942 – present) • Proved that black holes emit radiation and eventually evaporate • Theory of Everything… there is a movie about him… YOU should watch it