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Image PowerPoint Chapter 1 Astronomy Today, 5th edition Last revised: 25-Jan-10 Chaisson McMillan © 2005 Pearson Prentice Hall This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials. Learning Goals for this Chapter • • • • • • • • • What is the scientific method? Scientific notation, units and prefixes The celestial sphere & angular measurement Motion of the Sun, Moon & stars in the sky Phases of the Moon Precession of the Earth’s axis The sky clock & calendar – archaeoastronomy Lunar and solar eclipses Parallax measurements for distances and sizes Chapter 1 Opener Charting the Heavens: The Foundations of Astronomy Betelgeuse -Orionis 58 Orionis The Orion Constellation Orion’s Belt Orion Nebula (M42) Rigel One of 88 in the sky Sizes/Scales in the Universe Units and Scales • • • • • • Greek letters Scientific notation (powers of 10) SI Units (mks system) Fundamental constants Periodic Table of the Elements Atomic & molecular structure Greek Alphabet Scientific Notation Numbers are written in form of a x 10b Ordinary decimal notation Scientific notation (normalized) 300 3×102 4,000 4×103 5,720,000,000 5.72×109 −0.0000000061 −6.1×10−9 SI UNITS •Measurement system used all over the world except for 3 countries (US, Liberia & Burma) • Base units are the meter(m), kilogram(kg) & second(s) for length, mass & time • Other units made by combining these, e.g., velocity in m/s; acceleration in m/s2; force in kgm/s2 (= Newton) ; energy in N·m (= Joule); power in J/s (= Watt) Fundamental Constants Physical quantities that are generally believed to be both universal in nature and constant in time. Examples: Relative Standard Uncertainty Quantity Symbol Value speed of light in vacuum c 299 792 458 m·s−1 defined Newtonian constant of gravitation G 6.67428(67)×10−11 m3·kg−1·s−2 Planck constant h 6.626 068 96(33) × 5.0 × 10−8 −34 10 J·s proton mass mp 1.672 621 637(83) × 10−27 kg 1.0 × 10−4 5.0 × 10−8 PERIODIC TABLE OF THE ELEMENTS Atomic Number (Z) = #protons = #electrons Atomic Weight /Mass Number (#protons + #neutrons) ATOMIC & MOLECULAR STRUCTURE Helium Z=2 Lithium Z=3 Beryllium Z=4 Methane CH4 Methanol CH3OH Caffeine Figure 1-1 Earth = 15,000 x (3/5)mi/km =9000 mi Figure 1-2 The Sun X (3/5)mi/km = 900,000 mi sunspots Sunspots are About the size of the Earth! Figure 1-3 Spiral Galaxy (similar to our Milky Way) Latest News: Milky way thickness was thought to be 6000 ly. Now seems to be 12,000 ly. Figure 1-4 Galaxy Cluster (1 ly = 6 trillion miles) Figure 1-5 Sizes and Scales Figure 1-6 Scientific Method The Scientific Method The Traditional Scientific Method Figure 1-7 A Lunar Eclipse The Moon traveling through the shadow of the Earth Figure 1-8 Constellation Orion Naked eye view of bright stars In Orion Traditional stick figure constellation Constellations Constellations are now defined by the IAU as 88 areas of the sky. They usually contain the old star groups from earlier times. Asterisms vs. Constellations Asterism - Easily recognizable pattern of stars. Can be within a constellation (e.g., Big Dipper in Ursa Major) OR From more than one constellation (e.g., Summer Triangle – one star each from Lyra, Cygnus and Aquila) Centaurus Figure 1-9 Orion in 3-D To the ancients all stars were equidistant on the celestial sphere Once we could determine stellar distances then we found stars at Varied distances and moving in many directions Figure 1-10 Constellations Near Orion Figure 1-11 TheCelestial Sphere Figure 1-12 Northern Sky Seasons Caused by the 23½° tilt of Earth’s rotational axis to the ecliptic plane Ecliptic -The Apparent Path the Sun takes across the Sky Fall Equinox Spring Equinox Motion of Objects in Sky Relative to the Horizon Seasonal Movement of Sun in the Sky Seasonal Length of Days Seasonal Movement of Sunrise and Sunset Positions Picture of solar paths over the course of one year showing the change in sunrise/sunset positions on the horizon and the height of the Sun above the horizon at noon Some of the preserved examples of the thousands of examples of historic structures constructed by many civilizations to follow the motions of the Sun, Moon and stars in order to keep time. Figure 1-14 Typical Night Sky Summer Sky Winter Sky Figure 1-15 The Zodiac Constellations WINTER SPRING SUMMER Ecliptic FALL Solar (Relative to the Sun - the Sun overhead) and Sidereal Days (Relative to the stars - 360 degree rotation ) Solar day takes 4 minutes more to get Sun overhead Solar and Sidereal Months Toward a distant star Figure 1-19 Variations in the Solar Day Time Zones Figure 1-18 Precession: the path of the north celestial pole in the sky Period of 26,000 yrs Presently the “North Star” is Polaris In ancient Egypt the North star was Thuban In the distant future the North star will be Vega Figure 1-21 Lunar Phases Lunar Phases Rising & Settting Times Lunar Eclipse Earth’s shadow Figure 1-24 Total Solar Eclipse Solar Corona Eclipse Paths Figure 1-28 Eclipse Tracks Figure 1-25 Types of Solar Eclipses: Partial, Total & Annular Umbral shadow Figure 1-26 Moon is farther from Earth due to its elliptical orbit and therefore does not cover the Sun’s disk Earth Total Annular Partial Annular Solar Eclipse How can we explain why eclipses are seen so rarely by most of us living here on Earth. Why aren’t they seen every month of the year? Intersection of the ecliptic and lunar orbital planes Figure 1-27 Eclipse Geometry Lunar orbital plane is tilted 5 degrees from the ecliptic plane Line of Nodes Only when the Line of Nodes points towards the Sun can the Moon, Sun & Earth be on that line together and cause eclipses to occur More Precisely 1-1 Angular Measurement Units Figure 1-32 Parallax Geometry Figure 1-29 Triangulation Parallax Method of determining distances The Surveyor’s Method Figure 1-30 Geometric Scaling More Precisely 1-3a Measuring Distances with Geometry More Precisely 1-3b Measuring Diameters with Geometry Stellar Parallax d* = 1/θ* Examples: θ* = 1 arcsecond (˝ ) d* = 1/1 arcsec = 1 parallax arcsecond [parsec or pc] θ * = 0.002” d* = 1/0.002” = 1/(2.0x10-3)˝ = 0.5 x 10+3 pc = 500 pc = 500 (3.26 ly) ≈ 1600 ly This was first able to be done in 1838 by Friedrich Bessel when telescopes got good enough to see these very tiny angular movements of arcseconds. People in the past thought the Earth was flat. NO! They were sailors and they watched lunar eclipses. Both of these experiences told them the Earth was a spheroid. Ships sailed over the horizon appearing to disappear hull first and then the sails They reappeared in the opposite order. The Earth’s shadow on the Moon appears as a circle. Figure 1-33 Eratosthenes’ Method of Measuring Earth’s Radius About 200 BC More Precisely 1-2 Celestial Coordinates Declination (δ) 90°N to 90°S Right Ascension (RA) 0h0m0s to 24h 0 RA starts at the spring equinox pt. on the celestial sphere. This pt. moves due to precession so coordinates need to be recalculated for different “epochs”. At present that pt. is in Aries and we use Epoch 2000 or 2050 star charts. Stellar Catalogs • The following 3 slides show typical star catalog lists for the nearest stars to the Earth and the brightest stars seen from Earth • Note the columns of stellar properties such as their coordinates (RA & Declination) and their parallax/distances 25 BRIGHTEST STARS R.A. Decl. App. Mag. d* Spectral class Abs. Mag. Nearest Stars Nearest Stars (again) Most stars come in multiples!