# Cosmic Engine Notes

Our sun is just one galaxy star in the galaxy and ours is just one galaxy in the Universe Outline the historical development of models of the Universe from the time of Aristotle to the time of Newton Aristotle (approx. 350 BC)

His theory proposed:

* Earth was round, rather than flat

* Earth was the centre of the Universe and that the Sun, the Moon, and other visible planets, as well as a celestial sphere containing all the stars, revolved around the Earth, this model was known as a geocentric model (Earth in the centre) Aristarchus (240 BC)

He has an alternative view; he suggested:

* The Sun is much bigger than the Earth

* The Sun is at the centre of the Universe and the Earth orbits it * The Earth rotates on an axis once per day, producing the apparent motion of the Sun and stars * A model with the Sun at the centre is known as a heliocentric model Ptolemy (140 AD)

He suggested:

* The Earth is the centre of the heavens and the Earth is at rest and the Universe rotates around the Earth * He contrived an elaborate model of circles within circles that was remarkably successful in predicting the observed motions of the heavens – so successful it was adopted by the Roman Church as the ‘correct’ picture of the Universe Nicholas Copernicus (1514)

* He suggested the heliocentric model was true

* His work was branded as heretical; that is, a crime against the teachings of the Church – because of this action, it slowed the acceptance of Copernicus’s model Tycho Brahe (Late 1500’s)

He suggested: (his findings were an extraordinary achievement because he had no telescope) * His model was the combination of the geocentric and heliocentric model * His model had all of the planets (except the Earth) revolving around the Sun, while the Sun revolved around stationary Earth Johannes Kepler (Early 1600’s)

He suggested:

* It was an improved heliocentric model of the Universe

* His model said that the planets moved around the Sun, not in circles but in ellipses, and the mathematics was encapsulated in three laws: 1. The Law of Ellipses: each planet moves in an ellipse with the Sun at one focus 2. The Law of Areas: the speed of the planets along their elliptical orbits is such that they sweep out equal areas in equal periods of time. In effect, this means that the closer the planes are to the Sun, the faster they travel along their orbit 3. The Law of Periods: the period, T, of the orbit of a planet (that is, the time it takes to complete an orbit) is related to the average radius, Rav, of the orbit as follows: T2Rav3=k Galileo Galilei (1600)

* Was the first person to look at stars and planets

* He saw that Jupiter’s moon’s were orbiting it, not Earth this was proof that Ptolemy’s complicated geocentric model was incorrect * It was in favour of the Copernican (heliocentric model) * In 1616 the Church gave Galileo a warning to stop teaching the Copernican model, however he did not, In 1632 he published a book with all his findings, and as a result in 1933 spent the last nine years of his life in house arrest Sir Isaac Newton (approx. 1653)

* Deduced the Law of Universal Gravitational

* Gravity is a force that pulls masses together

* Every mass in the Universe exerts a force of gravity on every other mass * The force of gravity between two bodies is determined by their masses and distance between them: F=Gm1m2d2 The first minutes of the Universe released energy which changed to matter, forming star and galaxies: Outline the discovery of the expansion of the Universe by Hubble, following its earlier prediction by Friedmann: * Friedmann mathematically proved that the universe was expanding, but he made some assumptions in order to prove it. * He used Einstein’s equations to determine his own solutions about the universe and when he omitted Einstein’s cosmological constant from his equations then all his solutions suggested that...

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