Physics – Cosmic Engine

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Daniel Quinn

Research dot points from “The Cosmic Engine” section of the syllabus that are listed in preparation for a written response test.

THE COSMIC ENGINE NOTES

GLOSSARY

Parallax – the apparent movement of an object against a more distant background when viewed from a different angle

ARISTOTLE (~330 BC)

Questioned by very few for centuries Stationary, spherical earth at the centre of a series of 53 concentric, crystalline,

transparent spheres which carried the sun, the moon the planets and the stars, rotating on different axes. (a geocentric model)

No way to measure stellar distances the huge distances between stars were not accounted for they were placed in one sphere

Greek astronomy only focused with recording and predicting angular positions of these light-points.

Like Empedocles, thought earth only combinations of earth, air, fire and water with properties of cool, moist, hot and dry.

ARISTARCHUS OF SAMOS (~ 240BC)

A heliocentric model of the universe, placing the sun at the centre. All planets revolved around a fixed sun in circular orbits Earth rotated once a day on its axis and the moon revolved around the Earth

Did not gain wide acceptance for 18 centuries until Copernicus (1473 – 1543) redeveloped it

IGNORED BECAUSE:oIt defied common sense – We do not feel the Earth spinning or moving

oFailure of observers to detect any stellar parallax – under the model, stars should show a period shift in position to and fro against more distant stars over the course of the year as the Earth orbited around the sun.

oWas not detected until 1838 following careful telescopic observations

PTOLEMY (AD 120 – 180)

Most successful of early attempts to develop working model of universe Accounted for retrograde motion Planets are usually observed to move towards the east against the stationary

stars in the background. However, they are sometimes seen to move west at some stages.

This can be easily explained as the Earth in its orbits sometimes “overtake” other planets so they appear to be moving “backwards”.