Modelling Celestial Motion

Using Models Designers and engineers use models to help them solve problems without having to construct the real thing. Designers and engineers use models to help them solve problems without having to construct the real thing.

Using Models They may be cars. They may be cars.

Using Models They may be computer generated ship models. They may be computer generated ship models.

Using Models Or they may plan out entire cities. Or they may plan out entire cities.

Astronomical Models Astronomer also use models. They use them to explain things like celestial motion. Astronomer also use models. They use them to explain things like celestial motion.

Two Main Models There were two main models devised to explain the motion of the Sun, Moon, planets and stars. There were two main models devised to explain the motion of the Sun, Moon, planets and stars. One was the geocentric, or Earth-centered model. One was the geocentric, or Earth-centered model. The other was the heliocentric, or Sun- centered model. The other was the heliocentric, or Sun- centered model.

Geocentric Model As early astronomers looked up into the night sky they saw objects in the sky move from east to west. As early astronomers looked up into the night sky they saw objects in the sky move from east to west.

Geocentric Model Early Greek astronomers such as Aristotle and Ptolemy used concentric circles (circles within circles) to explain the motion. Early Greek astronomers such as Aristotle and Ptolemy used concentric circles (circles within circles) to explain the motion.

Geocentric Model As a result they developed the Geocentric or Earth- Centered Model to explain this motion. As a result they developed the Geocentric or Earth- Centered Model to explain this motion.

Geocentric Model Let’s slow things down… Let’s slow things down… Turn to p.435 Turn to p.435

Geocentric Model How did the model explain retrograde motion? How did the model explain retrograde motion? Simple, some planets had orbits within their orbits. Simple, some planets had orbits within their orbits. They were called epicycles. They were called epicycles.

Geocentric Model As Mars, Jupiter and Saturn orbited Earth, they made circular motions around their path. As Mars, Jupiter and Saturn orbited Earth, they made circular motions around their path. This was the apparent cause for the retrograde motion. This was the apparent cause for the retrograde motion.

Geocentric Model Physical representations such as this 3m model could predict phases of the Moon and eclipses. Physical representations such as this 3m model could predict phases of the Moon and eclipses.

Geocentric Model The model worked so well it remained the dominant theory for nearly 2000 years. The model worked so well it remained the dominant theory for nearly 2000 years.

Heliocentric Model The heliocentric model of the solar system was a revolutionary idea at the time. The heliocentric model of the solar system was a revolutionary idea at the time. It placed the sun at the center of our solar system. It placed the sun at the center of our solar system.

Heliocentric Model The heliocentric model of the solar system began to take root during the Renaissance. The heliocentric model of the solar system began to take root during the Renaissance. The Renaissance was a period from when scholars and scientists began to look at things in a different way. The Renaissance was a period from when scholars and scientists began to look at things in a different way.

Heliocentric Model The heliocentric model was proposed by Nicholas Copernicus, a Polish astronomer. The heliocentric model was proposed by Nicholas Copernicus, a Polish astronomer.

Heliocentric Model Copernicus theorized that the Sun, not the Earth, was at the center of our Solar System. Copernicus theorized that the Sun, not the Earth, was at the center of our Solar System. He also believed that the planets orbited the sun on what he called the Solar Plane. He also believed that the planets orbited the sun on what he called the Solar Plane.

Heliocentric Model An Italian astronomer, Galileo Galilei, furthered the work of Copernicus. An Italian astronomer, Galileo Galilei, furthered the work of Copernicus.

Heliocentric Model Using more advanced equipment, such as more accurate telescopes, he was able to observe more. Using more advanced equipment, such as more accurate telescopes, he was able to observe more.

Heliocentric Model Galileo determined that Jupiter had moons and that Venus had phases, just like Earth’s Moon. Galileo determined that Jupiter had moons and that Venus had phases, just like Earth’s Moon. All this supported the Heliocentric Model. All this supported the Heliocentric Model.

Heliocentric Model The Heliocentric Model still did not predict celestial events as accurately as the Geocentric Model. The Heliocentric Model still did not predict celestial events as accurately as the Geocentric Model. German mathematician Johannes Kepler discovered why. German mathematician Johannes Kepler discovered why.

Heliocentric Model Kepler discovered that the planet’s orbits were not circular but ellipses. Kepler discovered that the planet’s orbits were not circular but ellipses. This strengthened the Heliocentric Model. This strengthened the Heliocentric Model.

Heliocentric Model Isaac Newton’s discovery of gravity only strengthened the Heliocentric Model more. Isaac Newton’s discovery of gravity only strengthened the Heliocentric Model more. Now there was a reason why the planets moved the way they did, the Sun’s gravity. Now there was a reason why the planets moved the way they did, the Sun’s gravity.

Heliocentric Model In 1846 the Heliocentric Model was used in the discovery of a new planet. In 1846 the Heliocentric Model was used in the discovery of a new planet. Based on the movement of Uranus it was theorized another planetary body existed. Based on the movement of Uranus it was theorized another planetary body existed. When telescopes were trained on the predicted spot they discovered Neptune. When telescopes were trained on the predicted spot they discovered Neptune.

The Solar System Today With advanced telescopes and unmanned space probes we have been able to learn even more. With advanced telescopes and unmanned space probes we have been able to learn even more.

The Solar System Today Today we know we share our solar system with asteroids, meteors and comets. Today we know we share our solar system with asteroids, meteors and comets. All these objects are in orbit around the sun. All these objects are in orbit around the sun.

Homework Please finish reading section 13.3 Please finish reading section 13.3 Complete questions #1-5 Complete questions #1-5 Vocabulary Vocabulary Celestial Sphere Celestial Sphere Solar Plane Solar Plane Solar System Solar System