Bell Ringer 9/8

• OPINION QUESTION – How do you believe the solar system was formed?

Chapter 28

Formation of the Solar System

Big Bang Theory

•Theory that universe began as a point and has been expanding ever since

Solar System

• Theories rely on observation and data from probes sent into space

• Theories explain– Shape of solar system– Differences between planets– Nature of planetary surface

Stars & Planets form from interstellar clouds, which exist in space between the stars

http://www.astrographics.com/GalleryPrints/Display/GP0069.jpg

http://www.daviddarling.info/images/interstellar_cloud.jpg

Orion Cloud

Triangulum.nebula

http://upload.wikimedia.org/wikipedia/commons/thumb/7/74/Triangulum.nebula.full.jpg/563px-Triangulum.nebula.full.jpg

Interstellar Clouds

• Consist mostly of hydrogen and helium gas with small amounts of other elements and dust– Dust makes clouds look dark by blocking light– Dust also reflect starlight and makes clouds

look bright

How astronomers believe solar system formed

• Density of interstellar gas is low

• Gravity slowly draws matter together until the matter is concentrated enough to form stars and planets

Interstellar Cloud

• Collapse of cloud begins slowly but gradually gets faster

• Cloud becomes more dense at center• If rotating, the cloud spins faster as it

contracts, due to centripetal force.• (DEMONSTRATION)

Interstellar Cloud• Interstellar cloud that

formed our solar system collapsed into a rotating disk of dust and gas

• Concentrated matter at the center acquired enough mass to form the Sun

• Remaining matter gradually condensed to form planets

Interstellar Cloud

• Temperature varied greatly with location

• Different elements and compounds condensing, affected distribution of elements on the planets

–Depending on their distance from the Sun

Planetesimals

• Space objects built of solid particles that can form planets through collisions

Large Planets

• First to develop was Jupiter

–Increased in size through the merging of icy planetesimals that contained mostly lighter elements

• Saturn and the other gas giants formed same way– Not as large because Jupiter collected so much

material

Inner Planets

• Planets that formed near the young Sun

• Composed primarily of elements that resist vaporization

(didn’t become gassy)• Rocky and dense

Debris• Material that remained after the

formation of the planets and satellites• Some became icy objects known as comets

• Others formed rocky planetesimals known as asteroids

– Thousands of asteroids have been detected in the asteroid belt, which lies between Mars and Jupiter.

In-Class Assignment/Homework

Bell Ringer 9/9

• Explain in your own words how scientists believe our sun formed

28.1 B

Models of Solar System

Aristotle

• 3rd century BC

• Geocentric: Earth-centered solar system–did not explain retrograde

(backward) motion of planets

Aristotle

Ptolemy

• 3rd century AD

• Planets revolve around Earth in circles –epicycles to explain

retrograde motion

Ptolemy

Retrograde motion

• The apparent backward movement of a planet

• The changing angles of view from Earth create the apparent retrograde motion of Mars.

Tycho Brahe

• a Danish astronomer

• Made accurate observations of the planets’ positions

http://honolulu.hawaii.edu/distance/sci122/Programs/p10/Brahe.jpg

Nicolaus Copernicus

http://www.cgirb.com/images/copernicus.jpg

Copernicus• 16th century• Heliocentric: sun-centered

model• Earth and planets orbit the

sun in the same direction, but at diff. speeds and distances

Copernicus

• Solves problem of retrograde motion

• 1700’s Galileo proves this with telescope

In-Class Assignment/Homework

• Ancient Astronomers WKT

Bell Ringer 9/10

• Who said our solar system was geocentric?

• Who said it was heliocentric?

Kepler

• 17th century

• Used observations of his teacher, Brahe, to explain planetary motion.

Johannes Kepler

http://www.nasa.gov/images/content/65879main_kepler-portrait-330-427.jpg

Kepler

• Each planet orbits the Sun in a shape called an ellipse, rather than a circle

– An ellipse is an oval shape that is centered on two points.

http://ca.geocities.com/web_sketches/ellipse_notes/ellipse_arc_length/ellipse_eccentric_angle.gif

Kepler’s 1st Law

• Law of ellipses : planets orbit the sun not in a circle, but in an ellipse.

• Astronomical unit: average distance between the sun and the earth.

Kepler’s 2nd Law

• Law of equal areas: Earth moves fastest when closest to the sun–Line from the center of a

planet sweeps through equal areas in equal periods of time.

Kepler’s 3rd Law

• Law of periods: Relationship between distance from the sun and the orbit period.–Orbit period: the time required

for the planet to make one revolution around the sun.

Galileo Galilei

http://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Galileo.arp.300pix.jpg/300px-Galileo.arp.300pix.jpg

Galileo

First person to use a telescope to observe the sky

Discovered that four moons orbit the planet JupiterProved that not all celestial bodies

orbit Earth and Earth was not necessarily the center of the solar system

Isaac Newton

Isaac Newton• Inertia: objects want to move in

a straight line at constant speed until acted upon by an outside force

• Gravity: force that pulls them out of that straight line

In-Class Assignment/Homework

• WKT 87 – Kepler’s La

• #3 = Major axis – line that runs along diameter of ellipse, Semimajor axis – average distance between sun and the planet

• #4 = Eccentricity – shape of the planet’s elliptical orbit