1. Chapter 23 Key Terms
Solar System Planet Geocentric Theory Heliocentric Theory Orbit Ellipse Dwarf Planet Terrestrial Planet Jovian Planet Asteroid Comet Meteor Meteorite Moon

2. Chapter 23
Our Solar system

3. The Solar System
Can you name the 8 planets in their order from the sun?
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
New Horizons mission

4. Early Theories Geocentric Theory Problems:
Before Christ, people believed that the Earth was stationary and everything in our solar system revolved around the Earth
Philosophers such as Plato and Aristotle helped influence this theory
Problems:
Retrograde motion – some planets seemed to slow down, stop, and then back up when compared to the stars
Planets sometimes seemed large and close at times, and small and far away at other times

5. Early Theories
Around the 2nd century AD, Ptolemy shifted the planet’s spheres so Earth was not at its center
Around the 16th century, Nicolaus Copernicus suggested that the Earth and planets moved around the sun
His work, The Revolutions, was published after he died and suggested his theories
Copernicus’s ideas were soon called the Heliocentric Theory
Copernican Revolution

6. Early Theories
Copernicus’s Heliocentric Theory still had a few problems
Several men contributed to his theory
Tycho Brahe: built special instruments and influenced another scientist (Kepler) to determine the true shape of orbits
Galileo Galilei: Observed moons orbiting Jupiter using his telescope
Johannes Kepler: Successfully described planetary motion
Formulated 3 laws
Planets move in ellipses with the sun at the focus
A planet moves faster when closer to the sun
The average distance from the sun and the time it takes a planet to orbit the sun always have the same mathematical relationship

7. Early Theories Keplers 3 laws are very important to astronomers
Space engineers rely on these laws to help plan space missions
Aphelion: when a planet is farthest from the sun
Perihelion: when a planet is closest to the sun
No theory provided why a planet followed the elliptical orbit
Isaac Newton
Developed a mathematical law to describe gravity

8. Planets
2006, the International Astronomical Union (IAU) redefined what a planet was
A body in the solar system that:
Orbits the sun
Has a spherical shape
Does not share the space of its orbit with any other object of significant size, other than moons
According to this classification, there are only 8 planets

9. Planets Dwarf Planets are objects that:
Orbit the sun
Are rigid and can be nearly spherical
Can share their orbits with other bodies of similar size
Are NOT satellites
The main difference between a planet and a dwarf planet is what is around the dwarf planet

10. Planets Terrestrial Planets Jovian Planets
Planets similar in size and density to Earth
Mercury, Venus, Earth, Mars
Also called the “inner planets”
Jovian Planets
Planets larger than Earth and have low densities
Sometimes called “gas giants” because they are made mainly of elements that are gases here on Earth
Jovian planets have greater surface gravity because of their size and mass

11. Planets Inferior Planets Superior Planets
Planets that orbit closer to the sun than Earth
Can only be seen near sunrise or sunset
Can cross in front of the sun - transit
Superior Planets
Planets farther from the sun than the Earth
Retrograde motion

12. Planets Mercury Venus Smallest planet
Temperatures on the day side can reach 800oF, while temps on the night side can plunge to -300oF
No moons
Venus
Opaque atmosphere
Tilted 177o on its axis
Highest surface temperature of any planet: 860oF

13. Planets Earth Mars 3rd planet from the sun
The most dense planet in the solar system
Mars
Very thin atmosphere
Has 2 very small moons
Contains the largest volcano in the solar system (Olympus Mons)

15. Planets Jupiter The largest planet in the solar system
The bands are made of ammonia compounds that move around the planet
The great red spot is actually a huge storm
Jupiter has many moons, but the 4 largest are the most well known: Io, Europa, Callisto, and Ganymede

17. Planets Saturn 2nd largest planet
Composition is so light, it would float in water
Has an extensive ring system
Has 62 moons, the largest is Titan
Has a large seasonal storm called the Great White Spot

18. Planets Uranus Neptune Known for its axial tilt – 97.8o 27 known moons
13 known rings
Has the blue color because of the light reflecting off the water molecules
Neptune
Farthest planet from the sun
13 moons, but only 2 are observable from Earth

21. Dwarf Planets
Orbit the sun, spherical shape, and can share their orbit with other objects of similar size
Pluto was discovered in 1929 by Clyde Tombaugh
Pluto has many unique characteristics
Orbital plane is tilted more than 17o to the ecliptic plane
Its orbit is more elliptical than any planet
Its perihelion is closer to the sun than Neptune’s perihelion
Its density is much less than the terrestrial planets, but it is believed to be mostly rock and ice
Forms a binary planet with its moon, Charon

22. Dwarf Planets
The discovery of Eris is what spurred the change in definition
Eris is almost twice as far from the sun as Neptune
There are 5 known dwarf planets
Pluto, Eris, Haumea, Makemake, Ceres

23. Small Solar System Bodies
Asteroids
The largest of the small solar system bodies
Size can range from a house to 1/3 of the moon
Cannot hold an atmosphere because of their weak gravity
Can be oddly shaped
Most asteroids have orbits in the asteroid belt (between Mars and Jupiter)
Two large asteroid families lie in the same orbit as Jupiter
Trojans
Greeks

24. Small Solar System Bodies
Comets
Small solar system body made of rock and ice that orbits the sun
May be chunks of frozen gas covered in gravel and dust
Two parts to the comet: head and tail
Two sections to the head
Nucleus: solid part
Coma: gaseous envelope that surrounds the nucleus
The tail only forms when the comet enters the inner solar system because of light pressure

25. Small Solar System Bodies
Meteoroids
Meteoroids are exactly like asteroids, except in size
Asteroids can be seen from Earth with a telescope, whereas meteoroids cannot
Meteors
A meteoroid that enters Earth’s atmosphere
Friction from the air causes it to heat up and glow
Meteorites
Meteors that reach the surface

26. Psalm 19:1
The heavens declare the glory of God; and the firmament sheweth his handywork.