Overview of Contemporary Astronomy
The First Evening


Quoting from Alan Lightman's, "A Modern Day Yankee In A 
Connecticut Court and other essays on Science".
Conversations with Papa Joe

The First Evening
  Read:   Conversations_with_Papa_Joe_I.pdf
  Listen: Conversations_with_Papa_Joe_I.mp3

  Key Words & Phrases:
    Crystal Clear Skys   
    Light Pollution
    Evolution of Stars
    Particle Accelerators 
    General Relativity
    Spinning Earth - Focault Pendulum
    Inverse Square Law
    Cepheid Variables (Shapley, Levett)
    Galaxies (and more galaxies)
    Globular Cluster

HOW DO WE KNOW THE EARTH SPINNING? Wikipedia - Foucault pendulum https://en.wikipedia.org/wiki/Foucault_pendulum The Foucault pendulum or Foucault's pendulum is a simple device named after French physicist Leon Foucault and conceived as an experiment to demonstrate the Earth's rotation. The pendulum was introduced in 1851 and was the first experiment to give simple, direct evidence of the earth's rotation. Foucault pendulums today are popular displays in science museums and universities.

HOW DO ASTRONOMERS MEASURE DISTANCES? Wikipedia -- Kepler's laws of planetary motion https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion The ratio of the square of an object's orbital period with the cube of the semi-major axis of its orbit is the same for all objects orbiting the same primary. This captures the relationship between the distance of planets from the Sun, and their orbital periods. Kepler enunciated in 1619 this third law in a laborious attempt to determine what he viewed as the "music of the spheres" according to precise laws, and express it in terms of musical notation. So it was known as the harmonic law. Kepler's Third Law states: T^2 ~ r^3 The discovery of phases of Venus by Galileo in 1610 was important. It contradicted the model of Ptolemy which considered all celestial objects to revolve around the Earth and was consistent with others, such as those of Tycho and Copernicus. In Galileo's day the prevailing model of the universe was based on the assertion by the Greek astronomer Ptolemy almost 15 centuries earlier that all celestial objects revolve around Earth (see Ptolemaic system). Observation of the phases of Venus was inconsistent with this view but was consistent with the Polish astronomer Nicolaus Copernicus's idea that the solar system is centered on the Sun. Galileo's observation of the phases of Venus provided the first direct observational evidence for Copernican theory. Wikipedia -- Astronomical unit https://en.wikipedia.org/wiki/Astronomical_unit The AU was originally conceived as the average of Earth's aphelion and perihelion; however, since 2012 it has been defined as exactly 149,597,870,700 m. The astronomical unit is used primarily for measuring distances within the Solar System or around other stars. It is also a fundamental component in the definition of another unit of astronomical length, the parsec. Wikipedia -- Parallax https://en.wikipedia.org/wiki/Parallax To measure large distances, such as the distance of a planet or a star from Earth, astronomers use the principle of parallax. Here, the term parallax is the semi-angle of inclination between two sight-lines to the star, as observed when Earth is on opposite sides of the Sun in its orbit.[a] These distances form the lowest rung of what is called "the cosmic distance ladder", the first in a succession of methods by which astronomers determine the distances to celestial objects, serving as a basis for other distance measurements in astronomy forming the higher rungs of the ladder. Wikipedia -- Henrietta Swan Leavitt - Standard Candles https://en.wikipedia.org/wiki/Henrietta_Swan_Leavitt Henrietta Swan Leavitt (July 4, 1868 - December 12, 1921) was an American astronomer. A graduate of Radcliffe College, she worked at the Harvard College Observatory as a "computer", tasked with examining photographic plates in order to measure and catalog the brightness of stars. This work led her to discover the relation between the luminosity and the period of Cepheid variables. Leavitt's discovery provided astronomers with the first "standard candle" with which to measure the distance to faraway galaxies. Wikipedia -- Harlow Shapley https://en.wikipedia.org/wiki/Harlow_Shapley Harlow Shapley (November 2, 1885 - October 20, 1972) was an American scientist, head of the Harvard College Observatory (1921-1952), and political activist during the latter New Deal and Fair Deal. Shapley used Cepheid variable stars to estimate the size of the Milky Way Galaxy and the Sun's position within it by using parallax. In 1953 he proposed his "liquid water belt" theory, now known as the concept of a habitable zone. Wikipedia -- Cosmic distance ladder https://en.wikipedia.org/wiki/Cosmic_distance_ladder The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A real direct distance measurement of an astronomical object is possible only for those objects that are "close enough" (within about a thousand parsecs) to Earth. The techniques for determining distances to more distant objects are all based on various measured correlations between methods that work at close distances and methods that work at larger distances. Several methods rely on a standard candle, which is an astronomical object that has a known luminosity. The ladder analogy arises because no single technique can measure distances at all ranges encountered in astronomy. Instead, one method can be used to measure nearby distances, a second can be used to measure nearby to intermediate distances, and so on. Each rung of the ladder provides information that can be used to determine the distances at the next higher rung. Wikipedia -- Hubble's law https://en.wikipedia.org/wiki/Hubble%27s_law Hubble's law, also known as the Hubble-Lemaitre law, is the observation in physical cosmology that galaxies are moving away from the Earth at velocities proportional to their distance. In other words, the further they are the faster they are moving away from Earth. The velocity of the galaxies has been determined by their redshift, a shift of the light they emit to the red end of the spectrum. Hubble's law is considered the first observational basis for the expansion of the universe and today serves as one of the pieces of evidence most often cited in support of the Big Bang model. The motion of astronomical objects due solely to this expansion is known as the Hubble flow. It is often expressed by the equation v = H0D, with H0 the constant of proportionality-Hubble constant-between the "proper distance" D to a galaxy, which can change over time, unlike the comoving distance, and its speed of separation v, i.e. the derivative of proper distance with respect to cosmological time coordinate. (See uses of the proper distance for some discussion of the subtleties of this definition of 'velocity'.) Hubble constant is most frequently quoted in (km/s)/Mpc, thus giving the speed in km/s of a galaxy 1 megaparsec [3.26 ly] away, and its value is about 70 (km/s)/Mpc. However, the SI unit of H0 is simply s^-1 and the SI unit for the reciprocal of H0 is simply the second. The reciprocal of H0 is known as the Hubble time. Tests of Big Bang Cosmology http://edu-observatory.org/olli/tobbc/index.html http://edu-observatory.org/olli/tobbc/Week1.html

EVOLUTION OF STARS - MAIN SEQUENCE Wikipedia -- Main sequence https://en.wikipedia.org/wiki/Main_sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung-Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell. Stars on this band are known as main-sequence stars or dwarf stars. These are the most numerous true stars in the universe, and include the Earth's Sun. After condensation and ignition of a star, it generates thermal energy in its dense core region through nuclear fusion of hydrogen into helium. During this stage of the star's lifetime, it is located on the main sequence at a position determined primarily by its mass, but also based upon its chemical composition and age. The cores of main-sequence stars are in hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward pressure of gravitational collapse from the overlying layers. The strong dependence of the rate of energy generation on temperature and pressure helps to sustain this balance. Energy generated at the core makes its way to the surface and is radiated away at the photosphere. The energy is carried by either radiation or convection, with the latter occurring in regions with steeper temperature gradients, higher opacity or both. The main sequence is sometimes divided into upper and lower parts, based on the dominant process that a star uses to generate energy. Stars below about 1.5 times the mass of the Sun primarily fuse hydrogen atoms together in a series of stages to form helium, a sequence called the proton-proton chain. Above this mass, in the upper main sequence, the nuclear fusion process mainly uses atoms of carbon, nitrogen and oxygen as intermediaries in the CNO cycle that produces helium from hydrogen atoms. Worth While Rabit Hole -- Solar neutrino problem https://en.wikipedia.org/wiki/Solar_neutrino_problem Main-sequence stars with more than two solar masses undergo convection in their core regions, which acts to stir up the newly created helium and maintain the proportion of fuel needed for fusion to occur. Below this mass, stars have cores that are entirely radiative with convective zones near the surface. With decreasing stellar mass, the proportion of the star forming a convective envelope steadily increases. Main-sequence stars below 0.4 Solar masses undergo convection throughout their mass. When core convection does not occur, a helium-rich core develops surrounded by an outer layer of hydrogen. In general, the more massive a star is, the shorter its lifespan on the main sequence. After the hydrogen fuel at the core has been consumed, the star evolves away from the main sequence on the HR diagram, into a supergiant, red giant, or directly to a white dwarf.

BOOK RECOMMENDATIONS: 365 Starry Nights; An introduction to Astronomy for every night of the year by Chet Raymo https://www.amazon.com/365-Starry-Nights-Introduction-Astronomy/dp/0671766066 365 Starry Nights is a unique and fascinating introduction to astronomy designed to give you a complete, clear picture of the sky every night of the year. Divided into 365 concise, illustrated essays, it focuses on the aesthetic as well as the scientific aspects of stargazing. It offers the most up-to-date information available, with hundreds of charts, drawings, and maps-that take you beyond the visible canopy of stars and constellations into the unseen realm of nebulae and galaxies. This simple yet substantial text is full of critical information and helpful hints on how to observe the stars; describe their position; calculate their age, brightness, and distance; and much more. Whether you observe the sky with a telescope or the naked eye, 365 Starry Nights makes the infinite intimate and brings the heavens within your grasp. Keep this invaluable, informative guide close at hand, and you'll find that the sky is the limit 365 nights a year. A Modern Day Yankee In A Connecticut Court: And Other Essays On Science by Alan Lightman https://www.amazon.com/Modern-Day-Yankee-Connecticut-Court/dp/0670812390 A second collection of brief essays, reflections, and tales by Harvard/Smithsonian Astrophysical Observatory physicist Lightman (Time Travel and Uncle Joe's Pipe). We meet the spectral Uncle Joe in this collection, too, in the first and longest essay in the book. Here, Lightman sets out to do no less than explain the past century of astrophysical discoveries--from star measurements to gravitational theories to black holes--as sort of an update for his no-nonsense relative. Alas, the device of the ghostly ancestor with a skeptical but inquiring mind was already cloying in volume I, so let us hope Lightman buries him next time around. For the rest, Lightman succeeds admirably in some predictable terrains: gravitational waves, extraterrestrial life, Halley's comet, what happened in the first moments of the Big Bang (impressed by Stephen Hawking's equations to define those initial conditions), and other matters astrophysical. Here Lightman demonstrates a gift for colloquial reductions of the complex that would be intelligible by junior high students. But the book's charm more often lies in the unexpected and the personal: an amusing tale that established a student's incompetence in an electronics lab; a bedtime conversation with his daughter about the camel's hump and the moon in the sky; the origins of snowflakes; a neurophysiological description of an encounter climaxed by a smile; a walk around Walden Pond. Lightman also displays a serious political side, inveighing against the new breed of star warriors who are elated at the thought of unleashing potent weapons in space--individuals who have never known war in their lifetimes. In homage to Swift, Lightman's "Modest Proposal" is to annihilate some measly third-world nation, already hopelessly in poverty and debt, so that the rest of the world could get a close-up view. The title essay is a bit about waking up in 1880 and being arrested for spouting all sorts of nonsense about being a creature of the 20th century. The trial is not going well as our hero realizes that he can't explain how a television set or a refrigerator works. But then comes a moment when he has to write something and produces a ballpoint pen. Acquittal promptly follows. A pleasantly mixed bag, then, with references provided for those who would like to read more. The Cosmological Distance Ladder: Distance and Time in the Universe by Michael Rowan-Robinson https://www.amazon.com/Cosmological-Distance-Ladder-Time-Universe/dp/0716715864 The scale of cosmological distances has been a topic of dramatic controversy during the past decade. Experts estimating the size of the universe, as measured by the Hubble constant, have differed by as much as a factor of two. Just how big is the universe, and why have distance measurements varied to greatly? Michael Rowan-Robinson sheds new light on the origins of this controversy, critically reviewing the main techniques of measuring distances between astronomical bodies both within and outside our galaxy. Stars, galaxies, and cluster of galaxies all play a major part in the distance ladder, and knowledge of distance is essential for all branches of astronomy. As we examine the geometrical speculations of the Greeks and the first correct estimates of the relative distances of the planets from the Sun by Copernicus we realize that this is also a history of mankind's expanding horizon. Offering a fair, balanced review and a clear synthesis of the variety of techniques and methods for measuring cosmological distances (including the work of Gerard del Vaucouleurs, Allan Sandage, Gustav Tammann, and others), Rowan-Robinson integrates the various distance-measuring methods and presents a new, revised distance scale for the known universe. He supplies a unique perspective on modern astronomy itself as he pursues and expanding scale of distance from the solar system outward. Extensively illustrated with photographs and line drawings. sam.wormley@gmail.com