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The Solar System. Chapter 20. Section 1-Observing the Solar System. Earth at the center- Centuries ago, the sun and stars moved across the sky while Earth seemed to remain stationary (still).

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the solar system
The Solar System

Chapter 20

section 1 observing the solar system
Section 1-Observing the Solar System
  • Earth at the center-
  • Centuries ago, the sun and stars moved across the sky while Earth seemed to remain stationary (still).
  • Greek Observations-several points of light seemed to wander across the sky among the stars. They called these PLANETS.
  • Mercury, Venus, Mars, Jupiter, Saturn
  • They thought that Earth was in a rotating dome called a celestial sphere.

Geocentric- an Earth centered model of the solar system

  • “geo” -Earth
  • Geocentric System-Earth is at the center of the revolving planets and stars.
ptolemy s model
Ptolemy’s Model
  • A.D. 140- Greek astronomer Ptolemy
  • developed the geocentric model
  • Astronomer- a scientist who studies
  • the universe beyond Earth.
  • His model had the Earth at the center with other planets moving on smaller circles that move on bigger circles.
  • This model was incorrect but showed how motions of planets are observed.
  • This geocentric model was accepted for over 1,500 years!
sun at the center
Sun at the Center
  • Not everyone believed the Earth being at the center.
  • Heliocentric was developed as the sun being the center of the solar system
  • “helios” – sun
  • In the heliocentric system, the Earth and other planets revolved around the sun.
  • People did not want to believe this system because it went against Earth being the center of the universe.
in a heliocentric system earth and the other planets revolve around the sun
In a heliocentric system, Earth and the other planets revolve around the sun.

copernican revolution
Copernican Revolution
  • 1543- Nicolaus Copernicus further developed the heliocentric model
  • Copernicus was able to work out the arrangement of the known planets and how they move around the sun.
  • Because this was against the church and the belief of the time, and Copernicus did not have enough evidence to support this idea, he did not publish his theories until after his death.
galileo s evidence
Galileo’s Evidence
  • 1610- Galileo Galileiused newly
  • invented telescope to make discoveries
  • that supported the heliocentric model.
  • He saw 4 moons revolving around Jupiter (proved not everything revolved around the Earth)
  • He also saw that Venus goes through phases similar to Earth’s moon which it would not have if it circled around the Earth.
  • The Heliocentric Model must be correct!
tycho brahe s observations
Tycho Brahe’s Observations
  • Copernicus correctly placed the sun as the center of the universe but incorrectly assumed the planets travel in orbits that are perfect circles.
  • Late 1500’s- Tycho Brahe and assistants studied and recorded the positions of the planets for 20 years without telescopes!
  • After Brahe died in 1601, his assistant Johannes Kepler continued analyzing observations.
kepler s calculations
Kepler’s Calculations
  • By studying Mars, Keplerfound that Mar’s orbit was an ellipse instead of a circle.
  • Ellipse- oval shape that is closely circular
  • Using the evidence gathered by Brahe, Kepler found that the orbit of each planet is an ellipse.
modern discoveries
Modern Discoveries
  • Since Galileo’s time, our knowledge of the solar system has increase dramatically.
  • We have discovered 3 more planets- Uranus, Neptune, and Pluto
  • Astronomers have discovered other objects in the solar system like comets and asteroids.
  • Today we know that the solar system consists of the sun, nine planets and their moon, and several kinds of smaller objects that revolve around the sun.
  • Galileo used a telescope to make observations as we do today but we have more technology and have placed telescopes in space as well as space probes to explore further into the far reaches of our solar system.
the sun
The Sun

Section 2

the sun s interior
The Sun’s Interior
  • The sun does not have a solid surface, but is a ball of glowing gas
  • ¾ mass is hydrogen, ¼ helium
  • Like the Earth, has an interior and atmosphere
  • The sun’s interior consists of the core, the radiation zone, and convection zone. (how does the sun work?)

3 parts of the sun
3 parts of the sun
  • The core- or ‘central region’
  • Energy comes from nuclear fission
  • Nuclear fission- a process where hydrogen atoms join together to form helium.
  • -this only occurs under extremely high pressure and temperature
  • -temperature in the core- 15 million degrees Celsius (27 mill. F)
  • Energy slowly moves out from the core into space.

The radiation zone- ‘middle layer’ a region of very tightly packed gas where energy is transferred mainly in the form of electromagnetic radiation.

  • Energy can take 100,000 years to move through this layer.
  • The convection zone- ‘outer most layer’ hot gases rise to the top from the bottom, cool, then sink forming loops of gas that move energy to the surface.
the sun s atmosphere
The Sun’s Atmosphere
  • Includes the photosphere, chromosphere, and the corona
  • The Photosphere- (inner layer) (‘photos’ – light) the sphere that gives off visible light. Considered the sun’s surface layer
  • The Chromosphere- (middle layer) (‘chroma’ – color) the sphere of color
  • The Corona- (outer layer) (‘corona’ – crown) extends into space and thins into streams of electrically charged particles called solar wind.
features on the sun
Features on the Sun
  • Features on or just above the sun’s surface include sunspots, prominences, and solar flares.
  • Sunspots- areas of gas on the sun’s surface that are cooler than the gases around them. Cool areas don’t give off much light and are darker.
  • huge reddish loops of gas (sunspots) extending over the edge of the sun
solar flares
Solar flares-
  • when loops connect releasing magnetic energy, erupting into space.
solar wind
Solar wind
  • Solar flares increase solar wind from the corona, which reach Earth’s upper most part of the atmosphere.
  • Normally blocked from Earth’s magnetic field and atmosphere, at the North and South poles, particles create powerful electric currents causing gas molecules to glow
  • Aurora- rippling sheet of light caused by solar flares
  • Solar wind particles effect Earth’s magnetic field creating magnetic storms, disrupting radio, tv, phone, and electrical power problems. (aurora) (solar wind) (song-why does the sun shine?)

4 inner planets
4 inner planets
  • Mercury, Venus, Earth, and Mars
  • The 4 inner planets are small and have rocky surfaces
  • Inner planets are also called terrestrial planets
  • Characteristics:
  • Water: Liquid water on the surface
  • 70% covered
  • Exists in all three forms: solid, liquid, and gas
  • Atmosphere:
  • Has enough gravity to hold gases
  • Nitrogen- 78% Oxygen- 20% and other gases such as Argon and Carbon Dioxide and water vapor.
  • The smallest terrestrial planet and closest to the sun
  • Characteristics:
  • A single probe called Mariner 10 in the mid 1970’s showed the surface with craters and plains
  • The surface has changed little over time.


Mercury’s Atmosphere:

  • Almost NONE!
  • Small mass of the planet- weak gravity
  • Extreme temperatures- Greatest out of all planets
  • During the day the surface reaches 430°C, at night (because of lack of atmosphere heat escapes to space) temp goes to -170°C
  • Size and mass similar to Earth and referred to as Earth’s twin or Sister planet
  • Density and internal structure similar to Earth’s.
  • Takes 7.5 Earth months to rotate around the sun and 8 months to rotate around on its axis. A day on Venus is longer than a Venus year!
  • Rotates East to West (space school)


Venus’s Atmosphere:

  • Super thick and always cloudy
  • Made mostly of sulfuric acid.
  • Atmosphere is 90 times greater than Earths and would crush you if you stood on Venus’s surface.
  • Carbon Dioxide traps heat in through the greenhouse effect
  • Temperature average: 460°C- hot enough to melt lead.
venus continued
Venus Continued
  • Probes have visited Venus.
  • Venera- 1970, Magellan- 1990 mapped entire surface
  • Covered with rock with volcanoes and plains formed by lava flows
  • “Red Planet”- iron rich rocks
  • Atmosphere:
  • More than 95% Carbon Dioxide- similar to Venus but thinner
  • You could walk on Mars but would need a tank of oxygen
  • Few clouds and temperatures range from -140°C to 20°C (living on mars)

(how mars lost its atmos)


Mars’s Water:

  • Scientist think large amounts of water flowed on Mars’s surface in the distant past.
  • The atmosphere is so thin that any water will turn to gas.
  • Two frozen polar ice caps
  • Water may be frozen underground.
  • Mars’s Seasons:
  • Axis is tilted – has seasons like Earth
  • Northern and southern poles have different season so one ice cap grows and the other shrinks.
  • Windstorms cause dust to blow around
exploring mars
Exploring Mars
  • Many space probes have visited Mars.
  • NASA’s Spirit and Opportunity rovers have explored and examined rocks and soil samples, finding strong evidence of liquid water.
  • Several volcanoes flowed in Mars’s past but are inactive now. Olympus Mons is the largest volcano in the solar system. (curiosity) (planet rap)


The first 4 outer planets- Jupiter, Saturn, Uranus, and Neptune- are much larger and more massive than Earth.

  • They do not have a solid surface and often called Gas Giants.
  • The 5th planet, Pluto, is small and rocky like the terrestrial planets.
  • Gas Giants-
  • Composed of hydrogen and helium in liquid form
  • Strong gravitational force compared to terrestrial planets
  • Outer layers are extremely cold, inner layers temperatures increase
  • Have many moons
  • All have rings-small particles of ice and rock
  • The largest and most massive planet
  • Atmosphere:
  • Made of hydrogen and helium
  • The Great Red Spot- a storm larger than Earth, similar to a hurricane, and first observed in the mid-1600’s.


  • Dense core of rock and iron
  • Thick mantle made of liquid hydrogen and helium
  • Crushing weight of atmosphere- 30 million times stronger than Earth.
  • Jupiter’s Moons:
  • Galileo discovered Jupiter’s 4 largest moons- Io (has active volcanoes), Europa (icy crust covers liquid oceans), Ganymede (largest moon in solar system; larger than Mercury), and Callisto(covered with craters).
  • Dozens of others orbit around Jupiter
  • Second largest planet in solar system.
  • Only planet that is less dense than
  • water (it will float)
  • Atmosphere:
  • Mainly hydrogen and helium
  • Clouds and storms (hurricane discovered recently at the north pole)
  • Rings: (chunks of rock and ice)
  • Has most spectacular than any other planet
  • Broad and thin like a compact disc
  • Moons: Largest-Titan

First, let’s get something straight-


Your Anus: Human biology- organ near the end of the digestive system.

Uranus: Gas Giant, planet near the end of our solar system.


Uranus Atmosphere:

  • Looks blue-green because of methane in atmosphere
  • Has rings
  • Discovering Uranus:
  • 1781-William Herschel opened up the door
  • for active solar system study

Exploring Uranus:

  • Voyager 2 arrived and sent back close-ups showing only a few clouds
  • Uranus rotates in 17hrs
  • Uranus’s axis is tilted at 90 degrees from its vertical. (rotates top to bottom instead of side to side)
  • Believed a large object hit into Uranus and knocked it on its side.
  • Uranus Moons:
  • 5 largest have icy, cratered surfaces
  • Some have lava flows
  • Total of about 27 moons.
  • Cold, blue planet with visible clouds
  • Could be slowly shrinking, heating up interior, producing clouds and storms in atmosphere.
  • Discovery:
  • First as a mathematical prediction based on Uranus’s orbit.
  • Thought gravity of an unseen planet was affecting Uranus and discovered in 1846.

Exploring Neptune:

  • Voyager 2 discovered a Great Dark Spot, like Jupiter’s Great Red Spot, but did not last long. Spots seem to come and go.
  • Moons:
  • 13 moons- largest Triton(thin atmosphere and south pole covered with nitrogen ice)
  • Very different than gas giants
  • Pluto has a solid surface, much smaller and dense than outer planets.
  • Has a single moon: Charon which is more than half the size of Pluto and sometimes called a double planet.
  • Pluto’s orbit:
  • Takes 248 Earth years to revolve around the sun!
  • Very elliptical, brings it closer to the sun than Neptune
is pluto a planet
Is Pluto a planet?
  • Pluto is very small
  • Pluto may only be slightly larger than some of the other pieces of ice, rock, and dust that orbit in our solar system.
  • If astronomers had discovered these other objects, it may not have been called a planet.
  • Recently astronomers have discovered a larger body beyond Pluto but have not classified or named this as a planet yet.