Chapter 21 Lecture: Origins of Modern Astronomy PDF

Chapter 21 Lecture Earth Science Fourteenth Edition, Global Edition Origins of Modern Astronomy Jennifer Mangan James Madison University © 2015 Pearson Education Ltd.  Ancient Astronomy Ancient Greeks – Used philosop...

Chapter 21 Lecture Earth Science Fourteenth Edition, Global Edition Origins of Modern Astronomy Jennifer Mangan James Madison University © 2015 Pearson Education Ltd.  Ancient Astronomy Ancient Greeks – Used philosophical arguments to explain natural phenomena – Also used some observational data © 2015 Pearson Education Ltd.  Ancient Astronomy Ancient Greeks – Most ancient Greeks held a geocentric (Earth-centered) view of the universe “Earth-centered” view Earth was a motionless sphere at the center of the universe Stars were on the celestial sphere – Transparent, hollow sphere – Celestial sphere turns daily around Earth © 2015 Pearson Education Ltd.  Ancient Astronomy Ancient Greeks Seven heavenly bodies (planetai) – Changed position in sky – Seven wanderers Sun Moon Mercury Venus Mars Jupiter Saturn © 2015 Pearson Education Ltd.  Ancient Astronomy Ancient Greeks – Aristarchus (312–230 B.C.) was the first Greek to profess a Sun-centered, or heliocentric, universe – Planets exhibit an apparent westward drift Called retrograde motion Occurs as Earth, with its faster orbital speed, overtakes another planet © 2015 Pearson Education Ltd.  Ancient Astronomy Ancient Greeks – Ptolemaic system A.D. 141 Geocentric model To explain retrograde motion, Ptolemy used two motions for the planets – Large orbital circles, called deferents, and – Small circles, called epicycles © 2015 Pearson Education Ltd.  The Universe According to Ptolemy, Second Century A.D. © 2015 Pearson Education Ltd.  Retrograde Motion of Mars © 2015 Pearson Education Ltd.  Birth of Modern Astronomy 1500s and 1600s Five noted scientists – Nicolaus Copernicus – Tycho Brahe – Johannes Kepler – Galileo Galilei – Sir Isaac Newton © 2015 Pearson Education Ltd.  Birth of Modern Astronomy Nicolaus Copernicus (1473–1543) – Concluded Earth was a planet – Constructed a model of the solar system that put the Sun at the center, but he used circular orbits for the planets – Ushered out old astronomy © 2015 Pearson Education Ltd.  Birth of Modern Astronomy Tycho Brahe (1546–1601) – Precise observer – Tried to find stellar parallax The apparent shift in a star’s position due to the revolution of Earth – Did not believe in the Copernican system because he was unable to observe stellar parallax © 2015 Pearson Education Ltd.  Birth of Modern Astronomy Johannes Kepler (1571–1630) – Ushered in new astronomy – Planets revolve around the Sun © 2015 Pearson Education Ltd.  Kepler’s Law of Equal Areas © 2015 Pearson Education Ltd.  Birth of Modern Astronomy Johannes Kepler (1571–1630) – Three laws of planetary motion Orbits of the planets are elliptical Planets revolve around the Sun at varying speed There is a proportional relation between a planet’s orbital period and its distance to the Sun (measured in astronomical units (AU’s) – one AU averages about 150 million kilometers, or 93 million miles) © 2015 Pearson Education Ltd.  Birth of Modern Astronomy Galileo Galilei (1564–1642) – Supported Copernican theory – Used experimental data – Constructed an astronomical telescope in 1609 Four large moons of Jupiter Planets appeared as disks Phases of Venus Features on the Moon Sunspots © 2015 Pearson Education Ltd.  Galileo and Galilean Telescope Figure 21.13 © 2015 Pearson Education Ltd.  Birth of Modern Astronomy Sir Isaac Newton (1643–1727) – Law of universal gravitation – Proved that the force of gravity, combined with the tendency of a planet to remain in straight-line motion, results in the elliptical orbits discovered by Kepler © 2015 Pearson Education Ltd.  Orbital Motion of Earth and Other Planets © 2015 Pearson Education Ltd.  Constellations Configuration of stars named in honor of mythological characters or great heroes Today 88 constellations are recognized Constellations divide the sky into units, like state boundaries in the United States The brightest stars in a constellation are identified in order of their brightness by the letters of the Greek alphabet – alpha, beta, and so on © 2015 Pearson Education Ltd.  Positions in the Sky Stars appear to be fixed on a spherical shell (the celestial sphere) that surrounds Earth © 2015 Pearson Education Ltd.  Positions in the Sky Equatorial system of location – A coordinate system that divides the celestial sphere – Similar to the latitude-longitude system that is used on Earth’s surface – Two locational components Declination – the angular distance north or south of the celestial equator Right ascension – the angular distance measured eastward along the celestial equator from the position of the vernal equinox © 2015 Pearson Education Ltd.  Earth Motions Two primary motions – Rotation Turning, or spinning, of a body on its axis Two measurements for rotation – Mean solar day – the time interval from one noon to the next, about 24 hours – Sidereal day – the time it takes for Earth to make one complete rotation (360°) with respect to a star other than the Sun – 23 hours, 56 minutes, 4 seconds © 2015 Pearson Education Ltd.  Difference Between Solar and Sidereal Day © 2015 Pearson Education Ltd.  Earth Motions Two primary motions – Revolution The motion of a body, such as a planet or moon, along a path around some point in space Earth’s orbit is elliptical – Earth is closest to the Sun (perihelion) in January – Earth is farthest from the Sun (aphelion) in July The plane of the ecliptic is an imaginary plane that connects Earth’s orbit with the celestial sphere © 2015 Pearson Education Ltd.  Plane of the Ecliptic © 2015 Pearson Education Ltd.  Earth Motions Other Earth motions – Precession Very slow Earth movement Direction in which Earth’s axis points continually changes – Movement with the solar system in the direction of the star Vega – Revolution with the Sun around the galaxy – Movement with the galaxy within the universe © 2015 Pearson Education Ltd.  Precession of Earth © 2015 Pearson Education Ltd.  Motions of the Earth-Moon System Synodic month – Cycle of Moon through its phases – 29.5 days – Basis of first Roman calendar – Apparent period of Moon’s revolution around Earth Sidereal month – True period of Moon’s revolution around Earth – 27.3 days © 2015 Pearson Education Ltd.  Difference Between a Sidereal Month and a Synodic Month © 2015 Pearson Education Ltd.  Motions of the Earth-Moon System Lunar motions – Earth-Moon The difference of two days between the synodic and sidereal cycles is due to the Earth-Moon system also moving in an orbit around the Sun – Moon’s period of rotation about its axis and its revolution around Earth are the same, 27 1/3 days Causes the same lunar hemisphere to always face Earth © 2015 Pearson Education Ltd.  Motions of the Earth-Moon System Phases of the Moon – When viewed from above the North Pole, the Moon orbits Earth in a counterclockwise (eastward) direction – The relative positions of the Sun, Earth, and Moon constantly change – Lunar phases are a consequence of the motion of the Moon and the sunlight that is reflected from its surface © 2015 Pearson Education Ltd.  Phases of the Moon © 2015 Pearson Education Ltd.  Eclipses of the Sun and Moon Eclipses – Simply shadow effects that were first understood by the early Greeks – Two types of eclipses Solar eclipse – Moon moves in a line directly between Earth and the Sun – Can only occur during the new-Moon phase © 2015 Pearson Education Ltd.  Solar Eclipse © 2015 Pearson Education Ltd.  Eclipses of the Sun and Moon Lunar eclipse – Moon moves within the shadow of Earth – Only occurs during the full-Moon phase – For any eclipse to take place, the Moon must be in the plane of the ecliptic at the time of new- or full- Moon phase © 2015 Pearson Education Ltd.  Eclipses of the Sun and Moon Lunar eclipse – Because the Moon’s orbit is inclined about 5 degrees to the plane of the ecliptic, during most of the times of new and full Moon the Moon is above or below the plane, and no eclipse can occur – The usual number of eclipses is four per year © 2015 Pearson Education Ltd.  Lunar Eclipse © 2015 Pearson Education Ltd.