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The Solar System

Discover the wonders of the solar system - from the Sun to 9 planets and beyond. Learn about astronomy, electromagnetic spectrum, planetary orbits, and Earth's unique composition.

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The Solar System

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  1. Chapter 16 The Solar System

  2. Introduction • Astronomy – the scientific study of the universe beyond Earth’s atmosphere • Universe – everything, all energy, matter, and space • The Milky Way– 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 Intro

  3. Electromagnetic Spectrum Astronomers are interested in studying the full range of electromagnetic spectrum coming from space Intro

  4. Astronomy • 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 Intro

  5. 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 – 8 major planets with over 170 moons, 4 dwarf planets, and 1000’s of other objects (asteroids, comets, meteoroids, etc.) Section 16.1

  6. The Solar System • 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) Section 16.1

  7. Johannes Kepler (1571-1630) • German mathematician and astronomer • Kepler’s 1st Law – Law of Elliptical Orbits – All planets move in elliptical orbits around the Sun with the Sun as one focus of the ellipse • An ellipse is a figure that is symmetric about two unequal axes Section 16.1

  8. An ellipse has two foci, a major axis, and a semimajor axis 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 Drawing an Ellipse Section 16.1

  9. Kepler’s Second Law • Law of Equal Areas – An imaginary line (radial vector) joining a planet to the Sun sweeps out equal areas in equal periods of time Section 16.1

  10. 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 The speed of a revolving planet varies Section 16.1

  11. Kepler’s Third Law • 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 Section 16.1

  12. Major Planet Classification and Orbits in Our Solar System • 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 16.2

  13. Revolution/Rotation • 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). Section 16.2

  14. Planet Classification • Terrestrial planets – Mercury, Venus, Earth, Mars • High percent of more massive (non-gaseous) elements • Jovian planets - Jupiter, Saturn, Uranus, and Neptune • High percent of less massive gaseous elements Section 16.2

  15. The Solar System -- drawn to scale with the eight major planets Section 16.2

  16. A Planet’s Period • Sidereal Period – the time interval between two successive conjunctions as observed from the sun • Mercury’s sidereal period is 88 Earth days • Synodic Period – the time interval between two successive conjunctions of the planet with the Sun as observed from Earth • Mercury’s synodic period is 116 Earth days Section 16.2

  17. Mercury shown in inferior and superior conjunctions with Earth Section 16.2

  18. Planet Earth • 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 Section 16.3

  19. Composition of the 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: • Quartz – SiO2, Calcite – CaCO3, Feldspar – KAlSi3O8 • Note that most common minerals have oxygen (O) in their formula Section 16.3

  20. Earth’s Shape • The planet Earth is not a perfect sphere, but rather an oblate spheriod • 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 Section 16.3

  21. Albedo • 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 Section 16.3

  22. Earth Motions • 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) – see chapter 15 Section 16.3

  23. 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 Section 16.3

  24. Foucault Pendulum The pendulum does not rotate with reference to the fixed stars. Experimental proof of the Earth’s rotation Section 16.3

  25. Parallax • Parallax – the apparent motion, or shift, that occurs between two fixed objects when the observer changes position • Parallax can be seen with outstretched hand • The motion of Earth as it revolves around the Sun leads to an apparent shift in the positions of the nearby stars with respect to more distant stars Section 16.3

  26. Stellar Parallax • The observation of parallax is indisputableproof that the Earth revolves around the Sun. • In addition, the measurement of the parallax angle is the best method we have of determining the distance to nearby stars Section 16.3

  27. Aberration of Starlight • A 2nd proof of Earth’s orbital motion • Telescopic observations of a systematic change in the position of all stars annually • Due to the motion of the Earth around the Sun • Angular discrepancy between the apparent position of a star and its true position, arising from the motion of an observer relative to the path of the beam of light observed • This is similar to what you see when driving in the rain Section 16.3

  28. Aberration of Starlight • This discrepancy is very small and is measured in a -- parsec • Parsec parallax + second • Recall that a circle contains 360o. Each degree is divided into 60 minutes, and each minute into 60 seconds • Therefore 1 second = 1/3600 degree • Parsec = the distance to a star when the star exhibits a parallax of 1 second. Section 16.3

  29. Terrestrial Planets • 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 Section 16.4

  30. 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 • It has a density close to that of Earth. Section 16.4

  31. Mercury, a Terrestrial Planet The Messenger spacecraft mapped the surface of Mercury. It was the first spacecraft to orbit the planet. Rotates 3 times while circling the Sun twice Section 16.4

  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 Section 16.4

  33. The Atmosphere of Venus • 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 Section 16.4

  34. Venus, a Terrestrial Planet A radar map of Venus. The inset is from the Russian spacecraft Venera 13. Atmosphere rotates faster than solid planet. Retrograde rotation of planet Section 16.4

  35. Mars • 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 • The red color is thought to be due to fine grain iron oxide minerals. Section 16.4

  36. Martian Volcano – Mt. Olympus • The largest known volcano in the solar system, at 24 km in height, it is about three times that of Mauna Loa Section 16.4

  37. Mars at closest approach Section 16.4 Section 16.4

  38. Mars – Valles Marineris This canyon on Mars is 4000 km in length and 6 km deep Geologists think that it is a crustal fracture caused by internal forces Section 16.4

  39. In 2006 the Opportunity rover reached the edge of Victoria crater Section 16.4

  40. The Jovian Planets • Jupiter, Saturn, Uranus, Neptune • Much larger than the terrestrial planets • Composed mainly of hydrogen and helium • 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 Section 16.5

  41. Formation of the Terrestrial Planets • 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 • Leaving behind more of the massive elements and resulting in thick rocky cores and higher densities for the inner planets Section 16.5

  42. Formation of the Jovian Planets • 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 Section 16.5

  43. Jupiter • 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 • It is a fast rotator – taking about 10 hours to rotate. Section 16.5

  44. Jupiter Section 16.5

  45. 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 Section 16.5

  46. 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 Section 16.5

  47. Saturn and its rings Section 16.5

  48. 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 boulder-size particles (>1m), with very little dust-size • Average density of only 1.3 g/cm3 Section 16.5

  49. Uranus – unlike the other planets Uranus revolves around the Sun on its side and rotates in a retrograde fashion

  50. 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 Section 16.5

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