Sponge: List the five Moon phases. What are waxing and waning?

Ancient Astronomy

The scientific method involves theory and experimentation.

Prior to the acceptance of the scientific method, what scientists "thought" was accepted without being tested.

This held back the development of newer more correct theories for centuries.

Aristotle (384-322 B.C.) demonstrated one of the earliest uses of the scientific method.

He noticed that all lunar eclipses showed a curved shadow.

He concluded that since the shadow was always curved, then the Earth must be round. (A sphere is the only object whose shadow is always circular.)

He also argued that distant stars would appear at different positions to observers at different locations on the Earth if the Earth were round.

We use this difference in appearance to find the distance to stars. The method is called triangulation.

PARALLAX - the apparent shift of an object as seen from two different points of observation.

Closer objects form a "fatter" imaginary triangle.

Farther objects form a "thinner" imaginary triangle.

The amount of parallax is inversely proportional to an object's distance.

COSMOLOGY - the study of the workings of the universe on a large scale.

The ancient Greeks believed the universe to be comprised of the stars (which were attached to the celestial sphere), and the known components of the solar system: the Sun, Earth, Moon, and the five then known planets.

The parts of the solar system were obviously not part of the celestial sphere because they did not move like the stars.

They added additional spheres for the Sun and the Moon.

The Sun and Moon each move steadily and keep the same brightness.

Their location and appearance are easy to predict.

The explanation was not as easy for the other members of the solar system.

The planets: Mercury, Venus, Mars, Jupiter, and Saturn are not consistent in their movement and brightness. The name "planet" means "wanderer".

From night to night the planets generally move from west to east (as does the Moon); this is called direct motion.

However, the planets seem to speed up and slow down.

Three of the planets: Mars, Jupiter, and Saturn loop back and move east to west for a few months (retrograde motion).

Also, Mars, Jupiter, and Saturn are brightest during this retrograde motion.

These observations did not fit the simple cosmology offered by the ancient Greeks; however, few people questioned that this cosmology was correct.

THE GEOCENTRIC SOLAR SYSTEM

Aristotle (384-322 B.C.)

The Earth must be stationary because:1. The Earth doesn't feel like it's moving.2. We feel no strong wind from the motion.3. Why is there no parallax visible in the position of the stars?

The early models employed circles (the perfect curve, what else would God use?).

This cosmology was largely unchallenged until the 16th century.

Circles around the Earth worked well for the Sun and the Moon, but not for the planets.

For the planets, they added the epicycle to the deferent.

The best geocentric model of all time was constructed by the Greek astronomer Ptolemy around 140 A.D.

It was made of approximately 80 different circles.

The Ptolemaic cosmology was the accepted system for over 1000 years.

Aristarchus (310-230 B.C.) was one Greek who did question what was accepted by most others.

He suggested that a rotating Earth which orbited the Sun would explain the observations.

But Aristotle's influence was too great and his ideas persisted.

ANCIENT ASTRONOMY

Ancient astronomy was practical in nature.

Sailors and farmers.

Ancient astronomical sites

Stonehenge (England) - construction spanned 2000 years from 2800 B.C.

Carucol Temple (Mexico) - built by the Mayans around 1000 A.D.

Big Horn Medicine Wheel (Wyoming) – built by the Plains Indians.

Other cultures have great astronomical traditions: the Chinese and the Arabs are prominent figures.