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Transcript
4/26/2010 Introduction • Astronomy – the scientific study of the universe beyond Earth’s atmosphere • Universe – everything, all energy, matter, and space • Milky Way Galaxy – one of 50 billion galaxies scattered throughout the universe • Solar System – contains our sun and 9 planets • Sun – supplies the energy for nearly all life on the planet earth Chapter 16: The Solar System Homework: All questions on the “Multiple-Choice” and the odd-numbered questions on “Exercises” sections at the end of the chapter. Copyright © Houghton Mifflin Company. All rights reserved. 16 | 1 Copyright © Houghton Mifflin Company. All rights reserved. Electromagnetic Spectrum Intro 16 | 2 Astronomy Astronomers are interested in studying the full range of electromagnetic spectrum coming from space • But, much of the incoming solar radiation does not make it to the earth’s surface – due to atmospheric absorption • Electromagnetic radiation that will pass through the earth’s atmosphere can be studied using ground-based detectors • Other regions of the electromagnetic spectrum must be detected by space-based instruments – The Hubble Space Telescope is a good example of an instrument outside Earth’s atmosphere Copyright © Houghton Mifflin Company. All rights reserved. Intro 16 | 3 Copyright © Houghton Mifflin Company. All rights reserved. Telescopes at the top of Mauna Kea, Hawaii Intro 16 | 4 Astronomy - Relevance • Ancient Cultures – made numerous solar, lunar, and celestial observations – – – – 365-day year – solar cycle 29.5-day month – lunar cycle Calendars – agricultural & religious One of the Mayan calendars had 18 months of 20 days & 1 month of 5 days (365 days total) • Modern Cultures – celestial cycles still relevant – celebrate birthdays annually, – academic years, seasons, monthly bills Photo Source: Bobby H. Bammel Copyright © Houghton Mifflin Company. All rights reserved. Intro 16 | 5 Copyright © Houghton Mifflin Company. All rights reserved. Intro 16 | 6 1 4/26/2010 The Solar System The Solar System • The solar system - complex system of moving masses held together by gravitational forces • Sun is center • Sun is the dominant mass • Revolving around the sun -- 9 planets, over 70 moons, 1000’s of other objects (asteroids, comets, meteoroids, etc.) Copyright © Houghton Mifflin Company. All rights reserved. Section 16.1 • Geocentric Model – early belief that the earth was motionless and everything revolved around it – Claudius Ptolemy (A.D. 140) • Heliocentric Model – a sun-centered model – Nicolaus Copernicus (1473-1543) 16 | 7 Johannes Kepler (1571-1630) Section 16.1 16 | 8 Drawing an Ellipse • An ellipse has two foci, a major axis, and a semimajor axis • German mathematician and astronomer • Kepler’s 1st Law – Law of Elliptical Paths – All planets move in elliptical paths around the sun with the sun as one focus of the ellipse • An ellipse is a figure that is symmetric about two unequal axes Copyright © Houghton Mifflin Company. All rights reserved. Copyright © Houghton Mifflin Company. All rights reserved. Section 16.1 • In discussing the Earth’s elliptical orbit, the semimajor axis is the average distance between the earth and the sun Astronomical Unit (AU) = 1.5 x 108 km 16 | 9 Kepler’s Second Law Copyright © Houghton Mifflin Company. All rights reserved. Section 16.1 16 | 10 The speed of a revolving planet varies • Law of Equal areas – An imaginary line (radial vector) joining a planet to the sun sweeps out equal areas in equal periods of time • Perihelion – the closest point in a planet’s orbit around the sun, speed is the fastest – Perihelion occurs for Earth about January 4 • Aphelion – the farthest point in a planet’s orbit around the sun, speed is the slowest – Aphelion occurs for Earth about July 5 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.1 16 | 11 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.1 16 | 12 2 4/26/2010 Calculating the Period of a Planet Example Kepler’s Third Law • Calculate the period of a planet whose orbit has a semimajor axis of 1.52 AU • T2 = k R3 1y2 • T2 = AU3 x (1.52 AU)3 • T2 = 3.51y2 • Harmonic Law – the square of the sidereal period of a planet is proportional to the cube of its semimajor axis • T2 = k R3 • T = period (time of one revolution) • R = length of semimajor axis • k = constant (same for all planets) = 1y2/AU3 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.1 • T = 1.87 y • This is for Mars 16 | 13 Newton’s Correction 16 | 14 • Sun – 99.87% of the mass of solar system • Of the remaining 0.13%, Jupiter is > 50% • Planets with orbits smaller than earth are classified as “inferior” • Planets with orbits larger than earth are classified as “superior” Section 16.1 16 | 15 Revolution/Rotation • Section 16.1 Our Solar System • T2 = k R3 (Kepler’s) 4π2 • T2 = (m + m )G x R3 (Newton’s) 1 2 • This correction takes into account the mass of the bodies and their gravitational attraction • Rearranging the above equation will give 2 2 • (m1 + m2) T 3 = 4π R G Copyright © Houghton Mifflin Company. All rights reserved. Copyright © Houghton Mifflin Company. All rights reserved. Copyright © Houghton Mifflin Company. All rights reserved. Section 16.1 16 | 16 Section 16.1 16 | 18 Planet Classification All planets revolve (orbit) counterclockwise (prograde motion) around the sun as observed from the north pole. Each planet also rotates counterclockwise on its axis except Venus and Uranus (retrograde motion). • Terrestrial planets – Mercury, Venus, Earth, Mars – High percent of more massive (nongaseous) elements • Jovian planets - Jupiter, Saturn, Uranus, Neptune, and Pluto (?) – High percent of less massive gaseous elements Copyright © Houghton Mifflin Company. All rights reserved. Section 16.1 16 | 17 Copyright © Houghton Mifflin Company. All rights reserved. 3 4/26/2010 The Solar System Inclination of the planets’ orbit to earth’s The Solar System -drawn to scale Copyright © Houghton Mifflin Company. All rights reserved. Section 16.1 16 | 19 Copyright © Houghton Mifflin Company. All rights reserved. A Planet’s Period Section 16.1 16 | 20 Section 16.1 16 | 22 Mercury • Sidereal Period – the time interval between two successive conjunctions as observed from the sun • Synodic Period – the time interval between two successive conjunctions of the planet with the Sun as observed from earth • Sidereal = P1 P1 = 88 Earth Days • Synodic = P1 P1 P3= 116 Earth Days Copyright © Houghton Mifflin Company. All rights reserved. Section 16.1 16 | 21 Composition of the Earth Planet Earth • Atmosphere – 21% oxygen • Earth’s crust – over 90%, by volume, of the rocks/minerals are oxygen! • We live in an oxidized environment • Examples of very common minerals at the earth’s surface include: • The Earth is the third planet from the sun, and is a solid, spherical, rocky body with oceans and an atmosphere • Large amounts of surface water in all three phases – solid, liquid, and gas – exist on Earth • An oxygen-containing atmosphere, temperate climate, and living organisms all make Earth a unique planet Copyright © Houghton Mifflin Company. All rights reserved. Copyright © Houghton Mifflin Company. All rights reserved. Section 16.2 – Quartz – SiO2, Calcite – CaCO3, Feldspar – KAlSi3O8 • Note that most common minerals have oxygen (O) in their formula 16 | 23 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.2 16 | 24 4 4/26/2010 Earth’s Shape Albedo • The planet Earth is not a perfect sphere, but rather an oblate spheriod • Albedo – the fraction of the incident sunlight reflected by an object • Earth’s albedo is 33% • Moon’s albedo is 7% (from Earth the moon is the 2nd brightest object in the night sky) • Venus’ albedo is 76% (3rd brightest is sky) • Since the Moon is so close to Earth it is brighter than Venus – Flattened at the poles – Bulging at the equator – Due to rotation about its axis • Pole Diameter is about 43 km less than the Equatorial Diameter – Since the earth has an average diameter of 12,900 km this difference is only a small fraction Copyright © Houghton Mifflin Company. All rights reserved. Section 16.2 16 | 25 Earth Motions Section 16.2 16 | 26 Earth’s Rotation on its Axis • Not generally accepted until 19th century • Very difficult to prove • 1851, experiment designed by French engineer, Jean Foucault • The Foucault Pendulum – very long pendulum with a heavy weight at the end • Basically, the Foucault pendulum will swing back and forth as the earth moves under it • Daily Rotation on its axis (daily cycle) – Rotation – spin on an internal axis • Annual revolution around the sun (annual cycle) – Revolution – movement of one mass around another • Precession – the slow change of the earth’s rotational axis (now at 23.5o) – chapter 16 Copyright © Houghton Mifflin Company. All rights reserved. Copyright © Houghton Mifflin Company. All rights reserved. Section 16.2 16 | 27 Foucault Pendulum Copyright © Houghton Mifflin Company. All rights reserved. Section 16.2 16 | 28 Terrestrial Planets The pendulum does not rotate with reference to the fixed stars. Experimental proof of the earth’s rotation • The terrestrial planets include: Mercury, Venus, Earth, Mars • Due to physical/chemical characteristics they resemble Earth • All four terrestrial planets are – Relatively small in size and composed of rocky material and metals – Relatively close together and close to Sun – Have no rings – Only Earth and Mars have moons – Only Earth has surface water and oxygen Copyright © Houghton Mifflin Company. All rights reserved. 16.2 Section 16.2 16 | 29 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.3 16 | 30 5 4/26/2010 Mercury • Mercury is the closest planet to the sun • Mercury has the shortest period of revolution (88 days), and is the fastest moving • Mercury was named by the early Greeks after the swift messenger of the gods • Temperatures on Mercury range from about 473oC on the side facing the sun to about 173oC on the dark side • Due to its small size and closeness to the sun, Mercury has practically no atmosphere The Terrestrial Planets, Jovian Planets, and Earth's Moon Copyright © Houghton Mifflin Company. All rights reserved. Section 16.3 16 | 31 Copyright © Houghton Mifflin Company. All rights reserved. Mercury, a Terrestrial Planet Section 16.3 16 | 32 Venus • Venus is the closest planet to Earth • Venus is the third brightest object in the sky • Due to its brightness it was named after Venus the goddess of Beauty • The surface of Venus cannot be seen from Earth, due to dense, thick clouds that cover the planet • Magellan radar images indicate that the surface of Venus is composed of black, hot rock – Most surface rocks appear to be volcanic Rotates 3 times while circling the Sun twice Copyright © Houghton Mifflin Company. All rights reserved. Section 16.3 16 | 33 The Atmosphere of Venus Copyright © Houghton Mifflin Company. All rights reserved. Section 16.3 16 | 34 Venus, a Terrestrial Planet • Venus’ atmosphere is composed of 96% CO2 • It is so dense that the surface of Venus has a pressure of 90 atm • The large percent of CO2 in the atmosphere results in high surface temperatures (477o C) due the “greenhouse effect” • Radar images have revealed relatively few impact craters – Most of these craters are fairly large, because the smaller incoming objects are consumed by Venus’s thick atmosphere Copyright © Houghton Mifflin Company. All rights reserved. Section 16.3 Atmosphere rotates faster than solid planet. Retrograde rotation possibly caused by impact?? 16 | 35 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.3 16 | 36 6 4/26/2010 Mars Martian Volcano – Mt. Olympus • Mars has a red color, as viewed from the Earth, and was named for the Roman god of war • The surface of Mars has two outstanding features that have intrigued scientists for decades; polar ice caps and extinct volcanoes • The ice caps are composed of frozen CO2 in the winter and CO2 vapor with frozen water in the summer Copyright © Houghton Mifflin Company. All rights reserved. Section 16.3 • The largest known volcano in the solar system, at 24 km in height, it is about three times that of Mauna Loa 16 | 37 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.3 16 | 38 Section 16.3 16 | 40 Mars – Valles Marineris This canyon on Mars is 4000 km in length and 6 km deep Mars, a Terrestrial Planet Geologists think that it is a crustal fracture caused by internal forces Copyright © Houghton Mifflin Company. All rights reserved. Section 16.3 16 | 39 Formation of the Terrestrial Planets The Jovian Planets • Jupiter, Saturn, Uranus, Neptune • Much larger than the terrestrial planets • Composed mainly of hydrogen and helium • The two least massive elements – H & He – were the most abundant when the planets started to coalesce about 5 billion years ago • Due to the heat from the sun most of these less massive elements escaped the gravitational pull of the inner planets – The four Jovian planets have a very low average density (approximately 1.2 g/cm3) • All four are thought to have a rocky core composed of iron and silicates • Thick layers of frozen methane, ammonia, and water are found above the core Copyright © Houghton Mifflin Company. All rights reserved. Copyright © Houghton Mifflin Company. All rights reserved. – Leaving behind more of the massive elements and resulting in thick rocky cores and higher densities for the inner planets Section 16.4 16 | 41 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 42 7 4/26/2010 Formation of the Jovian Planets Jupiter • The four large outer planets were much farther from the sun and therefore much colder • The Jovian planets retained most of their H and He which now surround their ice layers and innermost rocky cores • As a consequence the Jovian planets have a much lower average density • Largest planet of the solar system, in both volume and total mass • Named after the supreme Roman god of heaven because of its brightness and giant size • Diameter is 11 times Earth’s -- 318 times more mass than Earth • The average density of Jupiter approximately 1.3 g/cm3 • Jupiter is covered with a thin layer of clouds composed of hydrogen, helium, methane, ammonia, and several other substances Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 43 Jupiter Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 44 Jupiter’s Great Red Spot (“eye”) • The Great Red Spot has erratic movement, shape, color, and size – sometimes even disappearing • Likely a huge counterclockwise “hurricane-like” storm, lasting hundreds of years Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 45 Copyright © Houghton Mifflin Company. All rights reserved. Saturn Section 16.4 16 | 46 Section 16.4 16 | 48 Saturn • Distinctive system of three prominent rings – Rings are inclined 27o to orbital plane • The rings are thought to be composed of ice and ice-coated rocks (micrometers 10 m) • Most spectacular sight that can be viewed from Earth with a small telescope • Diameter is 9 times Earth’s -- 95 times more mass than Earth • Average density of only 0.7 g/cm3 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 47 Copyright © Houghton Mifflin Company. All rights reserved. 8 4/26/2010 Roche Limit (Tidal Stability Limit) Formation of Saturn’s Rings • Orbiting moons are held together by their gravity • As a moon comes closer to a planet the differential gravitational (tidal) force on it increases • As a moon is brought closer, a point is reached where the tidal force is greater than the internal gravitational forces holding the planet together – and the moon is torn apart • This critical distance is called the Roche limit • Saturn’s rings are thought to have originated as small moons that came within their Roche limit and were torn apart • The Roche limit of Saturn is approximately 2.4 times the planet’s radius • Saturn’s outer ring is located at a distance of 2.3 times the planet’s radius Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 49 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 50 Section 16.4 16 | 52 Uranus • Discovered in 1781 by William Herschel (1738-1822), an English Astronomer • Named after Uranus, the father of the Titans and the grandfather of Jupiter • Thin ring system composed of bouldersize particles (>1m), with very little dustsize • Average density of only 1.3 g/cm3 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 Uranus 16 | 51 Copyright © Houghton Mifflin Company. All rights reserved. Neptune Neptune • Discovered in 1846 by Johann Galle, a German astronomer • Englishman John Couch Adams and Frenchman U.J.J. Leverrier were mathematicians using Newton’s law of gravitation • They noted that Uranus’ motion was disturbed and predicted the location of another planet – this is how Galle eventually discovered Neptune Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 • Neptune also has a large dark spot similar to Jupiter’s and thought to be the result of large wind systems • Neptune and Uranus are similar in size and in the composition of their atmospheres • In many respects these two planets can be considered twins 16 | 53 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 54 9 4/26/2010 Pluto • Names for the god of outer darkness • Average density of only 1.65 g/cm3 • Discovered in 1930, by C.W. Tombaugh Neptune – Investigating discrepancies in the orbital path of Neptune and Uranus • Does not resemble either the terrestrial or Jovian Planets • Pluto is the only planet that has not been visited by a space probe Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 55 Pluto Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 56 Section 16.4 16 | 58 Pluto and its Satellite Charon • There are similarities between Pluto and Triton, of Neptune’s moons • Some scientists think that both are large asteroids captured from interplanetary space • If this is the case, Pluto has maintained its own orbital path, and Triton was captured by Neptune Copyright © Houghton Mifflin Company. All rights reserved. Section 16.4 16 | 57 Origin of the Solar System Major Questions Concerning Solar System • Any theory that purports to explain the origin and development of the solar system must account for its present form • According to our best measurements, our solar system has been in its present state for about 4.5 billion years • A valid theory for solar system formation – must be able to explain a number of major properties of our solar system Copyright © Houghton Mifflin Company. All rights reserved. Copyright © Houghton Mifflin Company. All rights reserved. Section 16.5 • Origin of material? • Forces that formed the solar system? • Isolated planets, circular orbits, in same plane? • Revolution (orbit) in the same direction? • Most Rotate in same direction (except two)? • Terrestrial versus Jovian planets? • Origin of the asteroids? • Origin of comets and meteoroids? 16 | 59 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.5 16 | 60 10 4/26/2010 Formation of the Solar System • Began with a large, swirling volume of cold gases and dust – a rotating primordial nebula • Contracted under the influence of its own gravity – into a flattened, rotating disk • Further contraction produced the protosun and eventually accreted the planets • As particles moved inward, the rotation of the mass had to increase to conserve angular momentum (like an ice skater bringing in her arms) Copyright © Houghton Mifflin Company. All rights reserved. Section 16.5 The Formation of the Solar System Condensation Theory 16 | 61 Other Planetary Systems 16 | 62 • A star with a large planet orbiting about it will have a small wobble superimposed on its motion as a result of gravitational effects • This change in motion (the wobble) is likely to be very slight, but in some cases may be detected as a Doppler shift of the star’s spectrum – In other words, we should be able to find clouds of gas and dust, primordial nebula, and protosuns, etc. • We should also be able to use gravitational effects to detect small wobbles in rotational objects in space Section 16.6 – As the star approaches the observer, the wavelengths are compressed (‘blue shift’) – As the star move away from the observer, the wavelengths are lengthened (‘redshift’) 16 | 63 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.6 16 | 64 System First Planets Discovered Beyond our Solar System Gravitational Effects • In 1992, using the Arecibo Observatory in Puerto Rico, astronomers reported the discovery of two objects revolving about a pulsar • The amount of wobble can be used to determine the planet’s mass (related to gravitational pull) • The wobble’s cycle time can be used to determine the orbital period • Once the orbital period is known, Kepler’s third law (T2= kR3)can be used to determine the planet’s average distance from the star Copyright © Houghton Mifflin Company. All rights reserved. Section 16.5 Gravitational Effects • Are there other planetary systems in the universe? • If so, we would expect to find some of these systems in different stages of formation Copyright © Houghton Mifflin Company. All rights reserved. Copyright © Houghton Mifflin Company. All rights reserved. Section 16.6 – Pulsars are very dense, rapidly rotating stars – Pulsars have a very precise rotation period – If the rotation period is disrupted, this would indicate the presence of an object rotating about the pulsar • These two objects are the first planets detected beyond our solar system 16 | 65 Copyright © Houghton Mifflin Company. All rights reserved. Section 16.6 16 | 66 11 4/26/2010 Planets Beyond our Solar System The Moon • There have now been approximately 80 planets detected around other stars • These findings strongly indicate the existence of many other planetary systems in the universe • Scientists are also searching for signals from extraterrestrial intelligence (SETI) • Equipment today is being used to scan wide frequency ranges over vast areas of the sky • Second brightest object in the sky • First manned lunar landing on July 20, 1969 • 5 other lunar landings – Apollo 12, 14, 15, 16, & 17. • Lunar material: by radiometric dating techniques – Mountain rocks – 4.4 to 3.9 billion years old – Plain rocks – 3.9 to 3.1 billion years old • No rocks older than 4.4 or younger than 3.1 billion years old have been found. Copyright © Houghton Mifflin Company. All rights reserved. Section 16.6 16 | 67 General Features • Revolution 29.5 days • Rotation 29.5 days • 5th largest moon (largest for the Terrestrial planets) • Mass 1/81 Earth • Gravity 1/6 Earth • No magnetic field Surface Appearance • Craters: 30,000 & up to 100’s kms; likely formed by meteorite impacts between 4.4 and 3.9 billion year ago. • Basins: flattened floors of larger craters • Plains: large, dark, flat areas on the moon believed to be craters formed by meteorite impact that then filled with volcanic lava; also called maria; surface covered by a layer of loose debris called regolith; similar to Earth’s volcanic rock • Rays: bright streaks extending outward from some craters • Rills: long, narrow trenches or valleys due to moonquakes • Mountains: as high as 6100 m (>19,000 ft) and appear to be formed in a circular pattern, bordering the lunar plains • Fault - a break or fracture in the surface of the moon, along which movement has occurred Composition of the Moon • • • • • Core, mantle, crust All thought to be solid Crust, thicker on one side Presently does not have a magnetic field Although, the rocks brought back show some magnetism, indicating that the moon had a slight magnetic field at the time of rock crystallization. Craters on the Moon Crater Rays Basin 12 4/26/2010 The Straight Wall • Rill Fault Wall • A unique steep slope The fault wall is 130 km long by 0.25 km in height. Lunar Motion Effects • – • • Relative Motions of the Moon and Earth Nodes: Two points at which the Moon’s path crosses the Earth’s ecliptic plane Moon Phases • Waxing: Illuminated portion grows larger • Waning: Illuminated portion grows smaller • New moon: Occurs for a short time while moon is on same meridian as Sun • Waxing crescent phase; 4 days • First quarter: 90° East of Sun; 7 days • Waxing gibbous phase; 10 days • Full moon: 180° east of sun; 14 days – Earth position between the Moon and the Sun • Waning gibbous phase, 18 days • Last quarter: 270° east of sun; 22 days • Waning crescent phase, 26-28days Orbital plane Approximately 5o with respect to earth’s orbital plane. Hence, it is possible for the moon to be directly overhead at any latitude between 28.5oN and 28.5oS. Both the earth’s rotation on its axis and the moon’s revolution around the earth are counterclockwise (from a N pole perspective). Albedo • Fraction of incident sunlight reflected by a surface • Moon’s albedo 0.07 • Earth’s albedo 0.33 Phases of Moon ~ 29.5 days 8 different phases 13 4/26/2010 Phases of the Moon As observed from any latitude north of 28.5oN Phases of the Moon The “observer” is looking south; therefore east is on the left. Eclipses • • – • – The shadows cast by the Earth and the Moon cast two different degrees of darkness Umbra – the darkest and smallest region A total eclipse occurs within the umbra region Penumbra – the semidark region A partial eclipse occurs within the penumbra region Solar Eclipses Positions of the Sun, Moon, and Earth During a Total Solar Eclipse The umbra and penumbra are, respectively, the dark and semidark shadows cast on the Earth by the Moon • Sun: Moon: Earth • Moon in “new” phase Lunar Eclipse Moon is near “full” phase Sun: Earth: Moon 14