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The Solar System The Sun • Fuses 4 H atoms into 1 He, some mass energy • 75% hydrogen, 25% helium • 99.8% of mass of solar system • Middle-aged star, average in size, brightness, temperature • Photosphere – generates most of the visible light • Chromosphere – middle layer, visible during solar eclipse • Corona – outermost atmosphere, generates solar wind Anatomy of the Sun • solar wind - (streams of charged particles) causes Northern Lights • solar flares – outbursts of UV, radio, X-ray radiation, interrupt radio, power on Earth. Solar Flare • prominences – large arches of gas trapped by magnetic fields. sunspots – “cooler” areas associated with flares & prominences, may affect Earth’s climate. Sun Spots 1:50 Solar Features The Development of Astronomy • Aristotle – first to propose that Earth is round, based on observations of the round shadow it cast on the moon during lunar eclipses. The Development of Astronomy • Eratosthenes - @ 200 B.C., accurately calculated the circumference of the Earth (39,400 km). Actual circumference is 40,075 km. • Geocentric (Earthcentered) model – proposed by early Greeks • shows sun, moon, and planets (Mercury, Venus, Mars, Jupiter, Saturn) orbiting stationary earth in perfect circles. Models of the Solar system Models of the Solar System Problem: Geocentric Model did not explain retrograde motion of planets. Models of the Solar System • Mathematical “proof” of Geocentric Model proposed by Greek Claudius Ptolemy in 150 A.D. • Planets orbited in epicycles while orbiting Earth. Could also have been used to explain phases of Venus. Models of the Solar System • Heliocentric (Sun-centered) model – first proposed by early Greeks • rejected because it didn’t ‘feel’ like the Earth was moving The Dark Ages of Astronomy • Few advancements made for 1,400 years after Ptolemy. The Birth of Modern Astronomy • Heliocentric theory revived by Nicholas Copernicus in 1543. • Proven true, explains retrograde motion. • Tycho Brahe – @ 1575 persuaded king of Denmark to build him an observatory. • Measured locations of heavenly bodies, especially Mars, far more precisely than anyone before. The Birth of Modern Astronomy The Birth of Modern Astronomy • Kepler’s First Law • Kepler's Laws II • Johannes Kepler - @1600, Tycho Brahe’s assistant • Developed 3 Laws of Planetary Motion 1) Planets move in an ellipse with the Sun at one focus. The Birth of Modern Astronomy • Kepler’s Second Laws of Planetary Motion 2)A line between Sun and planet sweeps over equal areas in equal time. The Birth of Modern Astronomy Johannes Kepler’s Laws of Planetary Motion 3)The square of a planet’s orbital period equals the cube of its distance to the Sun. Kepler vs. Brahe The Birth of Modern Astronomy Galileo Galilei – first to look into the sky with a telescope and discover • four moons orbiting Jupiter • planets are circular disks, not points of light like stars • Venus has phases, must orbit its source of light, smallest at full phase, largest at crescent • Moon’s surface not smooth, had mountains, craters, & plains (“seas”) • Sun had sunspots, tracked these to determine that the Sun rotates once in just under a month. • Work supported Copernicus’ view of universe. The Birth of Modern Astronomy Sir Isaac Newton – developed Universal Law of Gravitation Gravity • Every object in the universe attracts every other body with a force proportional to product of their masses and inversely proportional to the square of the distance between the centers of the masses. The Birth of Modern Astronomy Sir Isaac Newton – Laws of Motion 1) A body stays in a state of rest or uniform motion unless an outside force acts on it. Newton's First Law of Motion The Birth of Modern Astronomy Sir Isaac Newton – Laws of Motion 2) The net force (F) on a body is equal to its mass (m) multiplied by its acceleration (a), F=ma. The Birth of Modern Astronomy Sir Isaac Newton – Laws of Motion 3) Whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first body. The Birth of Modern Astronomy Newton also showed planets are kept in orbit by balance of gravity and inertia. The Birth of Modern Astronomy Newton redefined Kepler’s Third Law, • taking into account the masses of the bodies involved • Providing a method for determining the mass of a body when the orbital period of one of it’s satellites is known. Movement of Planets • Copernicus proposed that planets orbit Sun. • Kepler showed orbits are elliptical. • Newton showed planets are kept in orbit by balance of gravity and inertia. • Nebular Theory - swirling sphere of dust and gas (from exploded star) flattened into disk • matter at center became protosun • protoplanets formed from clumps of matter • protosun became hotter until fusion started • material spun off or knocked off from planets became moons Formation of Solar System Structure • Inner Planets – have nickel-iron cores and rocky crusts, more dense – few or no moons • Asteroid Belt – between Mars & Jupiter – unformed planet • Outer Planets – mostly gas, less dense – numerous moons – All have ring systems • Kuiper Belt – beyond orbit of Neptune, many short-period comets originate here • Oort Cloud – theoretical – source of long-period comets? Comets • About 200 periodic comets known. • Halley’s Comet returns every 76 years, first one whose return was predicted. • Made of ice and dust (“dirty snowballs”) left over from early Solar System. • Invisible except when near Sun (ice of nucleus vaporizes, forms long tail, always points away from sun). • Elliptical orbits, most extend far beyond Pluto. • Small nucleus, 16 x 8 x 8 km Meteorites • Bits of Solar System that have fallen to Earth • May be iron, stone, or stony-iron (in space called meteroids) • several hundred tons enter atmosphere each day • Meteors – glowing trail as they burn in atmosphere • Meteor showers – when Earth passes through trail of comet debris. • Meteor Crater, AZ was formed by iron meteorite 30-50 m in diameter. • Large one probably caused climate changes that led to dinosaur extinctions. Leonids Meteor showers are best after midnight because in the early evening (A) we are facing away from the debris cloud, and in the early morning (B) we are facing toward it. Tour of the Planets Inner Planets - Mercury • Closest to the sun, .38 AU. • No atmosphere or satellites (moons). • Slow rotation (3 rotations/2 revolutions), fast revolution (59 days). • Highly eccentric orbit. • Most extreme temperature change - day/night difference is 600° C (430°C/ -180°C.) • Most heavily cratered; no plate tectonics. • “Shriveled” surface, huge scarps (cliffs), highlands. • Marias like moon – old lava floods after impacts. Venus – 2nd from the Sun • • • • • • • • • • .72 AU from sun. Brightest planet in sky – cloaked in clouds. Shows phases (like the moon). No moons. Slow, backwards rotation; day nearly = year. Atmospheric pressure 90 times Earth’s. 97% CO2 atmosphere - runaway greenhouse effect. Rains sulfuric acid. Surface is hot enough to melt lead, 482o C, 900o F. Volcanically active (shield volcanoes, runny lava). Earth – 3rd from the Sun • • • • • • • • 1.0 AU (astronomical unit) from Sun recognized as a planet in 16th century core is hotter than surface of Sun densest body in solar system surface young because of plate tectonics only planet with liquid water Has one moon. moon is gradually slowing our rotation Mars – th 4 from Sun • thin atmosphere, no greenhouse effect • temp. -207 to 80F, avg. –67 F • Olympus Mons is highest mountain in solar system; old volcano (volcanoes no longer active.) • Valles Marineris is deepest, longest canyon in solar system – would stretch from LA to NYC. • water erosion evidence visible • Core cooled faster than Earth’s, lost most of it’s magnetic field & protection. • two moons– Phobos and Deimos The Asteroids • mostly between Mars and Jupiter • 7000+ known, some greater than 200 km diameter • total mass less than our Moon • some planet moons may be captured asteroids • Near Earth Asteroids could hit Earth Gas Giants – Jupiter – • • • • • • th 5 from Sun 4 moons discovered by Galileo in 1610 Has many other moons, rings 90% H, 10% He no surface, mostly liquid metallic hydrogen would be a star if 80X larger bands of high winds include permanent storm called Great Red Spot • huge magnetic field Europa •Smallest moon of Jupiter •Has icy crust •Thought to have liquid oceans beneath, kept from freezing by friction caused by Jupiter’s gravity. •Potential for life? Io – innermost moon of Jupiter, very active sulfur volcanoes. Ganymede, the largest moon in the solar system, bigger than Mercury. Saturn – 6th from Sun • observed through telescope by Galileo in 1610 • rings discovered by Huygens in 1659, thought to be unformed or shattered moon. • least dense planet, density less than water • more than 20 moons Uranus – 7th from sun • first planet discovered in modern times, by William Herschel in 1781 • Explored by Voyager 2 • axis tilted nearly 90 degrees; has rings • Greenish-blue due to methane gas. • 15 or more moons (Miranda – extreme terrain) Neptune • discovered from predictions based on irregularities in orbit of Uranus • sometimes the most distant planet • similar to Uranus, mostly methane • also has rings • winds over 2000 km/hr are fastest in Solar System Pluto • • • • Never visited by spacecraft has one large moon named Charon orbit highly inclined and eccentric more similar to comet or asteroid than true planet • probably made of rock and ice • temperature probably about -230 C The End This Solar System was brought to you by Mr. Imes, with considerable help from NASA space vehicles , the Hubble Telescope, and the generous support of the U.S. taxpayers.