Students will be able to:• Describe Ptolemaic model of the universe• Discuss contributions made by Aristotle, Aristarchus, Galileo, and Hubble• Understand Copernicus’ contributions to the heliocentric solar system• Describe Kepler’s three laws of planetary motion and• Understand how Newton’s Laws helped Kepler develop his laws of planetary motion.

Early Greeks believed that the Earth lay at the center of the universe. This is known as the “Geocentric” model.

Geo=EarthCentric=Centered

This model was proposed by a philosopher and mathematician named Claudius Ptolemy, who lived from AD90-AD168

Notice, there were seven bodies orbiting the Earth in the Ptolemaic Model

• The Sun• The Moon• Mercury• Venus• Mars• Jupiter• and SaturnAll other bodies in space appeared to be stationary.The area beyond the orbiting bodies was known as the firmament, or

the area of space that was infinite with fixed stars, aka “heaven”.

To the ancient Greeks, the stars traveled daily around the Earth on a transparent, hollow sphere called the celestial sphere. It was Aristarchus (312-230 BC) who first proposed the heliocentric model, that placed the Sun in the middle of everything. This was centuries BEFORE the accepted Ptolemaic model, which was geocentric.

Aristarchus came to this conclusion after very cleverly observing something called “retrograde motion”. Planets exhibit an

apparent westward drift.

In this photo series of Mars’ retrograde motion, you can see how it appears to double back on itself.

Aristotle was a Greek who studied under Plato, and knew that the Earth was a sphere, and that the light we see from the moon, is actually sunlight.

Known as the father of science because of his many observations, both accurate and inaccurate.

Aristotle believed in a geocentric model of the universe, and did not have knowledge of forces such as gravity or inertia, so Earth was static (unmoving).

1. Another name for an Earth-centered universe is______________ and the ____________ believed this because of improper observations.

2. In Ptolemy’s model of the universe, what was the firmament?

3. What model correctly placed the Sun at the center?

4. Who was it who first proposed a helio-centric model?

5. Whose model did Aristotle’s observations support?

These years were known as the time of the birth of modern astronomy. The big 4 were:• Nicolaus Copernicus•Johannes Kepler• Galileo Galilei• Sir Isaac Newton

I’m sure you’ve heard most of their names before, but here is a brief synopsis of what each one contributed to the field of space science…

1473-1543

Copernicus was the first to • Conclude that Earth was a planet. • Prove Aristarchus’ thought that the Sun was at the center of things.• Usher in the new age of astronomy.

Copernicus continued to believe…in error…that the planets traveled around the sun in circular paths.

Of course, we know today, that the planets orbit the Sun in “elliptical” paths.The Earth’s path in this diagram is greatly exaggerated, however, it

also shows how the Earth’s gravitational field could influence the Sun’s motion. When the Earth is closest to the Sun in its orbit (a point called Perihelion), as small as we are, we do influence the Sun slightly, pulling it towards us.

6. What were Copernicus’ contributions to astronomy?

7.What were Copernicus’ misconceptions about astronomy?

8.What shape is the actual path of the planets around the Sun?

9.At what point is the Earth closest to the Sun, during its annual journey?

1571-1630

Kepler:•Proved that planets revolve around the Sun• Founded the three laws of planetary motion:

Orbits of the planets are elliptical Planets revolve around the Sun at varying speeds There is a proportional relationship between a planet’s orbital period and its distance to the Sun (as measured in AUs)

If it takes the Earth the same amount of time to travel from A-B, as it does for it to travel from C-D, then it is obvious that the Earth will travel faster when it is closest to the Sun (at perihelion)

Kepler's third law of motion states the obvious. The relationship between the orbital period of a planet and its distance from the Sun is direct. This relationship is mathematical and can be summarized in the equation:

P2 = d3 0r p2 = a3

In the equation, "p" stands for the orbital period of the planet measured in years and "a", for the average distance of the planet from the Sun measured in astronomical units.

If it takes a planet 8 years to revolve around our sun, what is the size of its orbit (how many AUs?)

p2 = d3 or p2 = a3

So: 82 = a3

Or: 64 = a3

Or: a = 4You can also do this in reverse. If a planet has an orbital distance of 5 AUs, how long does it take the planet to revolve around the Sun?

p2 =d3 or p2 = a3

So: p2 = 53

Or: p2 = 125Or: a = 11.18 years

The significance of Kepler's third law is that given the period of revolution of any body, be it a planet or a moon, one can calculate the size of its orbit.

1564-1642Galileo • found evidence to support Copernican theory• Used experimental data• Constructed an astronomical telescope in 1609

Found four large moons around Jupiter Discovered features on the moon Discovered sunspots

1643-1727

Sir Isaac Newton set forth:• The law of universal gravitation• that the force of gravity, combined with the tendency of a planet to remain in straight-line motion (inertia), resulted in the elliptical orbits discovered by Kepler.

10. What were Kepler’s contributions to the science of astronomy?

11. What are the 3 Laws of Planetary Motion?

12. Write and describe Kepler’s equation that summarizes his 3rd Law.

13. What were Galileo’s main contributions to astronomy?

14. What were Isaac Newton’s contributions to astronomy?

In 1919, the prevailing view of the cosmos was that the universe consisted entirely of the Milky Way Galaxy.

Using the Hooker Telescope at Mt. Wilson, Hubble identified Cepheid variables (a kind of star) in several spiral nebulae, including the Andromeda Nebula and Triangulum.

His observations, made in 1922–1923, proved conclusively that these nebulae were much too distant to be part of the Milky Way and were, in fact, entire galaxies outside our own.

Hubble also devised the most commonly used system for classifying galaxies.

Long after his death, the launching of the Hubble Space Telescope (named in honor of Hubble) in 1990 on the Space Shuttle, remains in low-Earth orbit taking photos of astronomical observations.

Hubble’s ultra deep field image reveals over 10,000 galaxies!

An AU, or Astronomical Unit, is defined as the average distance from the Earth to the Sun. This distance is: 149,500,000 kilometers. Jupiter is 779,000,000 km from the Sun. How many AUs is Jupiter from the Sun?

1 : ?149,500,000

779,000,000

779,000,000 = 149,500,000X

779,000,000 = 149,500,000X149,500,000 149,500,000

779,000,000 = X149,500,000

5.21 = X so Jupiter is 5.21 AUs from the Sun

15. Venus is 108,208,930 km from the Sun. How many AUs is Venus from the Sun?

16. What were Hubble’s biggest contributions to the understanding of the universe?

1 : ?149,500,000

108,208,930

108,208,930 = 149,500,000X

108,208,930 = 149,500,000X149,500,000 149,500,000

.7238 = X or .7238 AUs

In your journals, construct a “Trace” Map (combination Tree, and Brace) of the contributing scientists, mathematicians, and philosophers to the science of astronomy. • Begin with a tree map of contributors (how

many branches?)

• Construct a brace at the end of each branch with their contributions.

Etc…