1. 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.

2. Early Greeks believed that the Earth lay at the center of the universe. This is known as the “Geocentric” model. Geo=Earth Centric=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 Saturn All 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”.

3. 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.

4. 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…

5. 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. 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)

7. 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: P 2 = d 3 0r p 2 = a 3 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?) p 2 = d 3 or p 2 = a 3 So: 8 2 = a 3 Or: 64 = a 3 Or: a = 4 You 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? p 2 =d 3 or p 2 = a 3 So: p 2 = 5 3 Or: p 2 = 125 Or: 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.

8. 1564-1642 Galileo 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

9. 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. 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 149,500,000 779,000,000 = X 149,500,000 5.21 = X so Jupiter is 5.21 AUs from the Sun Venus is 108,208,930 km from the Sun. How many AUs is Venus from the Sun? 1 : ? 149,500,000108,208,930 108,208,930 = 149,500,000X 149,500,000.7238 = X or.7238 AUs

11. 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!

12. Supernovas may occur in two ways: After the core of an aging massive star (red giant) stops creating energy from nuclear fusion, it may undergo sudden collapse into what they call a neutron star or black hole, releasing gravitational potential energy that heats and expels the star's outer layers. Alternatively, a white dwarf star may accumulate sufficient mass from a stellar companion (through accretion, or merger) to raise its core temperature high enough to undergo runaway nuclear fusion, completely disrupting it.

13. As you may remember reading in our lab, our sun is in the “main sequence” of its life. The layers of the Sun show temperature highest at the core and progressively decreasing as we move out towards the exterior. The whole of solar mass is gaseous and mostly composed of hydrogen and helium. As the hydrogen is replaced by helium (nuclear fusion), these numbers flip-flop during its life At its core, the Sun fuses 620 million metric tons of hydrogen each second. At this average distance, light travels from the Sun to Earth in about 8 minutes and 19 seconds, and is largely emitted by the photosphere. The only time we truly get to see the sun’s corona (atmosphere) is when there is a solar eclipse.