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.
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 16 th 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 17 th 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 1 st 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 2 nd 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 3 rd 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 Jupiter Proved that not all celestial bodies orbit Earth and Earth was not necessarily the center of the solar system
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