NJIT Physics 320: Astronomy and Astrophysics – Lecture I Carsten Denker Physics Department Center for Solar–Terrestrial Research

September 3, 2003NJIT Center for Solar–Terrestrial Research Introduction  History of Solar Physics  Prehistoric era  Ancient Greek  Paradigm shift in planetary models  “Modern” Solar Physics  Why bother … ?  Most of the material has been stolen from the HAO Education Pages by Paul Charbonneau (NCAR, HAO)HAO Education Pages

September 3, 2003NJIT Center for Solar–Terrestrial Research Stonehenge (3000 – 1600 BC)

September 3, 2003NJIT Center for Solar–Terrestrial Research Solar Observations BC  3 May 1375 BC or 5 March 1223 BC: eclipse record on clay tablet uncovered in the ancient city of Ugarit, Syria  8 th century BC: Babylonians were keeping a systematic record of solar eclipses, predictions based on numerological rules  800 BC: Oldest record of a sunspot observations are found in the Book of Changes, China  250 BC: Measurement of the distance to the Sun by Aristarchus of Samos (ca BC).

September 3, 2003NJIT Center for Solar–Terrestrial Research Ancient Greek  Physical (geocentric) model of the cosmos by Aristotle (384 – 322 BC)  Mathematical model of planetary motion by Ptolemy (100 – 170), terrestrial/celestial sphere, basic elements: earth, water air, and fire/quintessence The Aristotelian cosmos. The Earth sits motionless at the center of the universe, and the outer sphere, the Primum Mobile, is assumed to undergo a full revolution in 24 hours.

September 3, 2003NJIT Center for Solar–Terrestrial Research Early Observations of the Corona  Report of solar eclipse observations by the Byzantine historian Leo Diaconus (950 – 994) on December 22 nd, 968 from Constantinople (now Istanbul, Turkey).  Possible eclipse record on oracle bones dating from the Shang dynasty in China (1766 – 1123 BC)  Chronicle of Novgorod describes a prominence during the May 1 st, 1185 solar eclipse: "In the evening there as an eclipse of the sun. It was getting very gloomy and stars were seen... The sun became similar in appearance to the moon and from its horns came out somewhat like live embers." Annales Sangallenses: "...at the fourth hour of the day... darkness covered the earth and all the brightest stars shone forth. And is was possible to see the disk of the Sun, dull and unlit, and a dim and feeble glow like a narrow band shining in a circle around the edge of the disk".

September 3, 2003NJIT Center for Solar–Terrestrial Research Sunspot Observations  Official records of the Chinese imperial courts starting in 165 BC  Theophrastus (374 –287 BC) including details of umbra and penumbra  Aristotelian views concerning the incorruptibility of the heavens meant that sunspots were "physically impossible", sightings were ignored or ascribed to transit of Mercury or Venus across the solar disk From the Chronicles of John of Worcester: one of the first surviving sunspot drawing from a sighting on December 8 th, "... from morning to evening, appeared something like two black circles within the disk of the Sun, the one in the upper part being bigger, the other in the lower part smaller. As shown on the drawing."

September 3, 2003NJIT Center for Solar–Terrestrial Research Nicholas Copernicus (1473–1543)  De Revolutionibus Orbium Coelestum in 1543  Heliocentric planetary model: The Sun is at the center of all planetary motions, except for the Moon which orbits Earth. Under this arrangement the orbital speed of planets decreases steadily outwards, and the outer sphere of fixed stars is truly motionless. In Copernicus' original model the Earth has three motions: a daily 24-hr axial rotation, a yearly orbital motion about the Sun, and a third motion, somewhat related to precession which Copernicus thought necessary to properly reproduce ancient observations.

September 3, 2003NJIT Center for Solar–Terrestrial Research Orbital Paths of Planets  Collection of 20 years of accurate planetary positions by Tycho Brahe (1546 – 1601)  Johannes Kepler (1571 – 1630)  1609: Astronomia Nova  1619: Harmonice Mundi  1627: Rudolphine Tables

September 3, 2003NJIT Center for Solar–Terrestrial Research Galileo Galilei (1564 – 1642) First telescopic observations of the Sun!

September 3, 2003NJIT Center for Solar–Terrestrial Research Sun as a Star – Maunder Minimum  René Descartes (1596 – 1650) describes the Sun as a star in his 1644 book Principia Philosophiae  Maunder minimum 1645 –1715: sunspots vanish even though a systematic solar observing program was underway under the direction of Jean Dominique Cassini (1625 – 1712) at the newly founded Observatoire de Paris

September 3, 2003NJIT Center for Solar–Terrestrial Research Isaac Newton (1642 – 1727)  1686: Principia Mathematica, universal law of gravitation  Stable planetary orbits result from a balance between centripetal and gravitational acceleration  Sun–to–Earth mass ratio (M Earth /M Sun = instead of ), wrong value for solar parallax, better estimate in later edition of the Principia (within factor of two)

September 3, 2003NJIT Center for Solar–Terrestrial Research Infrared Radiation  In 1800, William Herschel (1738 –1822) extended Newton's experiment of separating chromatic light components via refraction through a glass prism by demonstrating that invisible "rays" existed beyond the red end of the solar spectrum.

September 3, 2003NJIT Center for Solar–Terrestrial Research Spectroscopy  The English chemist and physicist William Hyde Wollaston (1766 – 1828) noticed dark lines in the spectrum of the Sun while investigating the refractive properties of various transparent substances  Joseph von Fraunhofer ( ) independently rediscovered the “dark lines” in the solar spectrum

September 3, 2003NJIT Center for Solar–Terrestrial Research Chemical Composition of the Sun Reproduction of part of the map of the solar spectrum published in 1863 by Kirchhoff, showing the identification of a large number of spectral lines with various chemical elements. Note numerous clear matches for Iron (Fe).

September 3, 2003NJIT Center for Solar–Terrestrial Research Sunspot Cycle Heinrich Schwabe (1789 –1875)

September 3, 2003NJIT Center for Solar–Terrestrial Research The First Solar Photograph 1845 The first successful daguerrotype of the Sun, reproduced below, was made on April 2 nd, 1845 by the French physicists Louis Fizeau ( ) and Léon Foucault ( ). The exposure was 1/60 of a second. This image shows the umbra/penumbra structure of sunspots, as well as limb darkening.

September 3, 2003NJIT Center for Solar–Terrestrial Research Sunspot Numbers  Statistics of sunspot number by Swiss astronomer Rudolf Wolf ( )  Relative sunspot number: r = k (f + 10 g), where g is the number of sunspots groups visible on the solar disk, f is the number of individual sunspots (including those distinguishable within groups), and k is a correction factor that varies from one observer to the next (with k = 1 for Wolf's own observations) Sunspot drawings by Johann Hieronymus Schroeter (1745 – 1816), an active solar observer between 1785 and Schroeter's sunspot drawings were a primary source for Wolf's reconstruction of activity cycle number 4 (1785 –1798)

September 3, 2003NJIT Center for Solar–Terrestrial Research Differential Rotation  Richard C. Carrington (1826 – 1875) Spörer's Law of sunspot migration. The thick lines shows the latitude] at which most sunspots are found (vertical axis, equator is at zero), as a function of time (horizontal axis). The dashed line is the Wolf sunspot number, showing the rise and fall of the solar cycle.,  Gustav Spörer (1822 – 1895)

September 3, 2003NJIT Center for Solar–Terrestrial Research First Observation of a Solar Flare 1859 On September 1 st, 1859, the astronomer R. C. Carrington was engaged in his daily monitoring of sunspots, when he noticed two rapidly brightening patches of light near the middle of a sunspot group he was studying.

September 3, 2003NJIT Center for Solar–Terrestrial Research First Observations of a Coronal Mass Ejection 1860

September 3, 2003NJIT Center for Solar–Terrestrial Research The Magnetic Nature of Sunspots 1908 The magnetically–induced Zeeman splitting in the spectrum of a sunspot. Reproduced from the 1919 paper by G.E. Hale, F. Ellerman, S.B. Nicholson, and A.H. Joy (in The Astrophysical Journal, vol. 49, pp. 153–178). George Ellery Hale (1868–1938)

September 3, 2003NJIT Center for Solar–Terrestrial Research The Celestial Sphere  Greek Tradition   Copernican Revolution   Positions on the Celestial Sphere  Physics and Astronomy

September 3, 2003NJIT Center for Solar–Terrestrial Research Positions on the Celestial Sphere Reference Epoch 1950: m = s yr –1 n = ’’ yr –1 Earth precession period is 25,770 years.

September 3, 2003NJIT Center for Solar–Terrestrial Research Spherical Geometry Law of sines: Law of cosines for sides: Law of cosines for angles:

September 3, 2003NJIT Center for Solar–Terrestrial Research Proper Motion v  : transverse or tangential velocity v r : radial velocity

September 3, 2003NJIT Center for Solar–Terrestrial Research Synodic and Sidereal Period (inferior) (superior) PlanetSidereal Orbital Period [yr] Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto248.54

September 3, 2003NJIT Center for Solar–Terrestrial Research Retrograde Motion of Planets

September 3, 2003NJIT Center for Solar–Terrestrial Research

September 3, 2003NJIT Center for Solar–Terrestrial Research Zodiac

September 3, 2003NJIT Center for Solar–Terrestrial Research Physics and Astronomy  Astronomy = natural extension of human curiosity in its purest form  Paradigm shifts  Physical causes for observable phenomena  Astronomy + Physics = Astrophysics  Observations  analyze photons and particles  Tools: telescopes, post–focus instrumentation, and computers

September 3, 2003NJIT Center for Solar–Terrestrial Research Homework  Homework is due Wednesday September 10 th, 2003 at the end of the lecture!  Homework assignment: Problems 1.5, 1.6, and 1.7  Late homework receives only half the credit!  The homework is group homework (2–3 students)!  Homework should be handed in as a text document!