# Astronomy 1143 - Spring 2023

SYLLABUS: TR 9:35-10:55 AM

Mid-term tests are on the material covered in class during the given mid-term period.

We will be covering topics from all chapters in the recommended textbook. However, some of those topics will not be covered in class. You should know the material we do cover in class, and read corresponding material in the textbook.

The exam questions will be from the material covered in class. The daily topics listed below cover only the main points. Make sure to attend lectures and study powerpoint lecture files below.

There is no math required on the exams. They are composed of multiple choice questions to test basic concepts. But you are expected to know important facts, figures and the meaning of some equations.

## DAILY TOPICS

• Jan 10: Overview of syllabus; no proven connection between astrology and astronomy; since stars also move, the position of the Sun relative to the 12 Constellations of the Zodiac changes over centuries and is different from the dates given in the 'horoscope' section of newspapers; science and religion: faith vs. inquiry; ancient astronomy; use of Geometry by the Greeks, belief in the Geocentric system (Aristotle,Ptolemy), Geocentric model (Ptolemy) vs. the Heliocentric model (Copernicus); the Metric system - used in science and in all countries except the U.S.; powers of ten in exponents; Universal spatial and temporal history; observational astronomy.
• Jan 12: Ground and space astronomy - need space observations to cover all kinds of radiation, such as X-ray, UV, etc. that are absorbed by the atmosphere of the Earth. The distance scale; angular size; the Earth moves about 1 degree in its orbit around the Sun each day; basic fundamental constants such as speed of light, 1 AU = (E-S) distance, etc. distance measures in astronomy are the AU and the Light year (LY); parsec - another distance unit is based on the method of parallax. Angular distances; the Earth moves about 1 degree in its orbit around the Sun each day. PARALLAX: apparent change in angular position due to motion; define 1parsec (pc) = 1/alpha(arcseconds), where alpha is the angle usually mesured relative to the orbit of the E-S orbit. The Celestial Sphere - stars 'fixed' in the Sky as a globe; Ecliptic - path of the Sun in the Sky; Celestial Equator - extension of Earth's equator to the celestial sphere; Vernal (Spring) and Autumn Equinoxes and Summer and Winter Solstices, related to seasons. Celestial 'longitude' - Right Ascension, Celestial 'latitude' - Declination, enable the location of an object in the Sky.
• Jan 17, Tuesday: GEOCENTRIC MODEL: Ptolemy, Aristotle - All heavenly objects revolve around the Earth, with planets also describing Epicycles that account for the observed Retrograde Motion of outer (Superior) planets; HELIOCENTRIC MODEL (COPERNICUS) - The Sun is at the Center with all planets revolving around it in circular orbits (not quite correct, but basically right); Inferior Planets (Mercury, Venus) - orbits inside the Earth's orbit (inferior and superior conjuction), Superior Planets (Mars,Jupiter,etc.) with orbits outside (opposition and superior conjunction). Synodic (apparent) and Sidereal (w.r.t. stars) periods of revolution of planets around the Sun; e.g. Synodic period of Jupiter is 399 days, but its sidereal period is 11.9 years. The Copernican System - determination of relative distances of planets from the Sun from the angle of greatest eastern and western elongation (the maximum angular separation of the planet from the Sun as seen from the Earth); TYCHO - the most famous pre-telescopic astronomer; made careful observations of the orbit of Mars.
• Jan 19, Thursday: KEPLER's LAWS: First Law - planetary orbits are elliptical with the Sun at one focus; `eccentricity' (ellipticity) e = distance from center to a focus/ semi-major axis. Kepler's Laws (Contd.): Second law - planets trace out equal area triangles in equal time ('equal triangles law'); Third law - P-squared = a-cubed, or P*P = a*a*a, where P is the period in years, and a is the semi-major axis of the orbit in AU. The Earth and the Moon (or any two objects orbiting under gravity) revolve around a common center of mass called the Barycenter that lies 1700 kms inside the Earth. GALILEO: defended the Copernican Heliocentric system; first one to use the telescope; made many discoveries to support the Heliocentric model - phases of Venus, moons of Jupiter, Sunspots; also discovered mountains on the Moon, found that the Milky way is made of stars, etc; Galileo did pioneering experiments on gravity - "all things fall at the same rate regardless of weight or mass".
• Jan 24, Tuesday: Newton's Law of GRAVITATION - F (grav) = G * (m1*m2)/(r*r), i.e. the force of gravity between two masses is directly proportional to their product, and inversely proportional to the square of the distance between them; your weight is the force of gravity between you and the Earth, i.e. F = G * m(you) * M(Earth) / R(Earth)-squared; the constant G is known as the Universal gravitation constant and is the same for all masses in the Universe. Escape velocity, kinetic and potential energy, orbits, angular momemtum.
• Jan 26, Thursday: First mid-term exam Quiz 1 Curve for Quiz 1 is +2.5%.
• Jan 31, Tuesday: LIGHT and MATTER: spectroscopy, color (wavelength), electromagnetic spectrum - Gamma-Rays to Radio waves in increasing wavelength; Visible spectrum: 4000 - 7000 Angstroms; continuous, emission, and absorption spectra; LIGHT - electromagnetic energy. Spectrum of visible light, blue to red; waves and wavelength. Light does not require a medium to propagate (unlike water or sound waves); particle of energy or quanta are called photons; c = wavelength x frequency; color depends on wavelength. Blue light has higher frequency, hence shorter wavelength, than red light; the e.m. spectrum extends from gamma rays (highest frequency) to radio waves (longest wavelengths); visible light is a small part of the spectrum, from blue (4000 A) to red (7000 A), where A is the Angstrom unit = 100 millionth of a cm. The hotter an object the more energetic ("bluer") its light, and vice versa. Atoms and Light -- photons have energy E = h * nu, where nu is the frequency = c/wavelength (h is called the Planck's Constant); each photon has a definite wavelength and hence 'color'.
• Feb 2, Thursday: ATOMS and SPECTRA - Quantum Theory: The positively charged nucleus is surrounded by negatively charged electrons arranged in definite and discrete energy orbits. Electrons can absorb or emit photons at definite energies (wavelengths) equal to the energy difference between orbits e.g. H-atom has one electron and one proton. An electron in H-atom emits a photon at wavelength 6562 Angstroms (red color!) when jumping from the third to the second orbit. SPECTRUM of a source (e.g. the Sun) is its light resolved according to lines at characterstic wavelengths. Emission spectrum is bright `color' lines, i.e. light emitted by atoms at certain wavelengths; and absorption spectrum is dark lines i.e. energy removed by atoms at corresponding wavelengths. Demostration: Emission spectra from fluorescent Tubes with H, He, Ne, Hg, H2O, CO2, Ar.
• Feb 7, Tuesday: Continuous, absorption, and emission spectra from astronomical objects; spectra outside the visible range (say X-ray) is not seen by human eye, but but may be present nonetheless. Hydrogen - Lyman (UV), Balmer (visible), Paschen (IR) series of lines; Red line of H - 6562 Angstroms. The Sun has a surface temperature of 5600 K and emits its peak light at yellow color. Brightness (luminosity) increases as temperature to the fourth power; brigtness of a source decreases as the inverse of the distance; Inverse Square Law due to geometry -- the area of a sphere increases as 4*pi*radius-squared. DOPPLER Effect, and Red- and Blue-shift. TEMPERATURE: Kelvin and Celsius temperature scales; room temperature is about 300 K. Temperature T of `blackbodies' - perfect radiators and absorbers at one T, with peak radiation at one wavelength. Hubble's Law: v = H_o d --> velocity increases with distance of galaxies; implies expansion of the Universe; H_o is Hubble's constant; 1/H_o is the age of Universe (uncertainty due to measurement of vast distances); Cosmic Microwave Background (CMB); indicates uniform and isotropic expansion; however, recent results show accelerating expansion --> Dark Energy ? Rotation curves of galaxies are flat, rather than decreasing with radius --> Dark Matter? > Feb 9, Thursday: Einstein's Theory of RELATIVITY. First Postulate - speed of light 'c' is a universal constant independent of the velocity of the source or the observer; Second Postulate - All physical laws have the same form everywhere in the Universe; E = m*c-squared, i.e. mass and energy are equivalent; mass (inertia) increases with velocity; it takes an infinite amount of energy to accelarate any mass to 'c' - therefore impossible for an object (e.g. spacecraft) to travel at the speed of light; The Special Theory deals with constant relative velocity; the General Theory of Relativity deals with acceleration and gravity; Principle of Equivalence - acceleration and gravitation are equivalent; Astronauts are weightless because they are falling at the same rate as the floor of the shuttle in orbit; time 'flows' slower for a moving object (astronauts live slightly longer!).
• Feb 9, Tuesday : Stars - Properties and structure of the Sun; State of matter: 99.9% of matter in the Universe is in plasma state (free electrons and protons); 90% of matter is H, 7.8 % is He, and the rest of the elements of the Periodic Table comprise only 2%; stellar energy from thermonuclear fusion of H --> He; stellar structure: core, radiative zone and convection zone; photosphere: visible layer of the Sun; perfect disk appearance and limb darkening - outer layers are cooler and emit less energy than central regions; H- opacity: engative hydrogen ion layer absorbs visible to infrared radiation; than chromosphere, transition region and the corona; flares and mass ejections driven by magnetic activity. elements of the Periodic Table comprise only 2%.
• Feb 14, Thursday: Stars - Properties and structure of the Sun; State of matter: 99.9% of matter in the Universe is in plasma state (free electrons and protons); 90% of matter is H, 7.8 % is He, and the rest of the elements of the Periodic Table comprise only 2%; stellar energy from thermonuclear fusion of H --> He; stellar structure: core, radiative zone and convection zone; photosphere: visible layer of the Sun; perfect disk appearance and limb darkening - outer layers are cooler and emit less energy than central regions; H- opacity: engative hydrogen ion layer absorbs visible to infrared radiation; than chromosphere, transition region and the corona; flares and mass ejections driven by magnetic activity. elements of the Periodic Table comprise only 2%. Feb 14, Tuesday: Stellar Classification -stars are classified according to color and temperature. Hertzsprung-Russell (HR) diagram of luminosity L vs. temperature T; stellar classification scheme: O,B,F,G,K,M,L - ranging in T ~ 50,000 - 1000 K; numeral subdivision (e.g O5) according to T and strengths of characteristic atomic lines; color depends on peak emission wavelength of blackbody curve corresponding to surface T; Balmer series of H lies in the visible spectrum; stellar spectrum is classified according to strengths of atomic lines (e.g. A stars have strong H lines); stellar luminosity classes: I-V; e.g. the atomic lines (e.g. A stars have strong H lines); stellar luminosity classes: I-V; e.g. the Sun is a G2V star; L depends on T as well as radius (size) of star; the Main Sequence (MS) of HR diagram reflects that stars: (i) are in H-burning (H-fusion) stage, and (ii) spend most of their lifetimes on the MS.
• Study Guide Quiz 2. There may be questions from material NOT on the studyguide but covered in class.
• Feb 16, Thursday: mid-term quiz 2 (40 min).
• Feb 21, Tuessday: Stellar evolution and nucleosynthesis; after the H --> He burning pphase on the MS, stars evolve to other parts of the diagram depending on mass; low and high mass stars; low and intermediate mass stars: M < 8M(Sun) --> Red Giants --> White Dwarfs; High-mass stars: M > 8M(Sun) --> Neutron Stars; M > 25 M(Sun) --> Black Hole. Summary of stellar evolution --- Gravitational collapse is balanced by electro-electron repulsion --> electron degeneracy pressure with all electrons at same energy; Chandrasekhar Limit = 1.44 M(Sun), mass where electron degeneracy pressure balances gravity in white dwarfs, formed from stellar cores of low to intermediate mass stars M < 8 M(Sun) and with residual central core mass < 1.44 M(Sun); for massive stars with M > 8 M(Sun), when residual M (core) > 1.44 M(Sun), the core gravitationally collapses into neutron star or BH; Gravitational collapse and end of low-masss and high-mass stars; low-mass stars --> white dwarfs, high-mass stars --> neutron stars or BH; nuclear fusion continues until iron - not beyond since that requires energy rather than produce it; the iron core collapse leads to electrons falling into the nucleus and combining with protons to form neutrons --> extremely dense, hard matter; infalling matter towards the core then bounces off with great force that blows off the stellar envelope --> supernova explosion; leaveing behind the neutron star remnant if 1.44 M(Sun) < M(Core) < 3 M(Sun); heavier mass stars with mass > 25 M(Sun) leave M(Core) > 3 M(sun), and collapse even further into a BH because even neutron degeneracy pressure is unable to withstand gravity; Schwarzschild radius and event horizon --> radius of BH from where light can not escape.
• Feb 23, Thursday: Distance and luminosity; apparent and absolute magnitudes for measuring brightness; distance modulus (m-M) = 5 - 5 logd - 5; absolute luminosity at d = 10pc. GALAXIES: Centers of galaxies - black hole driven activity; mapping galaxies; 21 cm HI radio emission; distribution of matter; rotational velocity; dark matter and halo; Dark matter: rotation curves of galaxies are flat instead of Keplerian (velocity decreasing with radius). Expansion and acceleration of the Universe and Dark Energy; Hubble's law requires distances, such as determined from Period-Luminosity relation of Cepheid variable stars on the HR diagram.
• Feb 28, Tuesday: Olber's paradox: why is the sky dark at night?; Big Bang cosmology based on Hubble expansion provides the answer; but slight deviations from the Hubble v = H_od line noticed at high-z, indicating acceleration of expansion; Dark energy? (Einstein's cosmological constant!); uniformity of radiation background is surprising since matter should distort it; rapid exponential inflation right after the BB might be the answer; cruvature of spacetime and distribution of mater-energy.
• March 2, Thursday: Observatories and telescopes; reflecting mirrors and refracting lenses; telescope power = pi*r*r; ground based telescopes such as Large Binocular Telescope (LBT) and space based telescopes such as the Hubble Space Telescope (HST); two main components of a telescope: objective and eyepiece; former is the most important since the main function of a telescope is to collect and focus light through the objective; refracting vs. reflecting telescopes; chromatic aberration of lenses; large telescopes use reflecting mirrors; wavelength ranges of ground and space observatories; ground based radio telescopes at the long wavelength end and gamma-ray space-based observatories at the short wavelength end; spectrographs and spectra.
• Mar 7, Tuesday: The Main Sequence (MS) on the HR diagram indicates stellar: temperature, absolute luminosity and magnitude (not apparent brightness), which depend on mass. Cepheid variable stars are giant stars, are about 10 times the mass of the Sun, located above the MS, and important as cosmological distance indicators; their brightness varies periodically depending on their absolute luminosity; longer the period (days) more luminous the star; therefore, knowing their luminosity and apparent brightness gives the distance accroding to the distance modulus relation. Stellar fuel; nuclear energy and reactions; nucleosynthesisof elements; stellar evolution; evolutionary phases and tracks on the HR-diagram; supernovae and production of heavy elements; cosmic abundances.
• Mar 9, Thursday: Mid-Term Quiz 3. No curve
• Study Guide Quiz 3. As before, the study guide covers most but all the topics on the exam, which entails all material covered since the last quiz.
• Mar 21 Tuesday: Big Bang cosmology and nucleosynthesis, qualitative view of the history of the Universe; inflation, expansion, acceleration; redshift and distance scale. Three pillars of BB cosmology supported by observations: Redshift, CMB, primordial He abundance.
• Mar 23, Thursday: Radiation and matter dominated phases of the universe; recombination epoch -- atomic formation and radiation matter decoupling. Cosmological distance ladder: trignometric parallax, spectroscopic parallax, Cepheid variables, Tully-Fisher relation, Supernovae Type Ia. Matter and energy density in the Universe; Total (matter + energy) density rho and critical density rho_c determine flat, accelerating, closed universes; Omega = ratio of (visible matter, energy + dark matter + dark energy) to critical density of the universe required to balance expansion against gravitational collapse.
• Mar 28, Tuessday: Only 4% of matter and energy are directly observable; Omega and the fate of the Universe; Omega = rho/rho_c; state of the universe: Omega = 1, <1, >1; Omega_m + Omega_Lambda; the former refers to all matter (visible and dark) and tthe latter to dark energy reminiscent of Einstein's cosmological constant. General Relativity and Friedmann Equations; value of critical density; Omega = 1 implies dark matter and dark energy constitute about 95% of total density; shape and structure of the universe depend upon, and in turn determne, our view of the beginning and the end of the universe; acceleration vs. expansion; matter+energy density vs. dark energy (cosmological constant); matter and energy densities vs. age and volume of the universe. Einstein and Friedmann equations of General Relativity.
• Mar 30, Thursday: Large-scale structure: stars, galaxies, galaxy evolution; clusters of galaxies, superclusters, voids, etc.; galaxy "seeds" with inflation. CMB anisotropy due to matter distortions are small angular scales; formation of first stars and galaxies during reionization epoch; end of 'dark ages' that followed the recombination epoch.
• April 4, Tuesday: Lyman-alpha "forests" due to absorption of distant quasar light by intervening H-clouds at varying redshifts. History of the Universe: big questions. Hubble classification of galaxies: tuning-fork diagram - ellipticals, spirals, barred-spirals, irregulars; ellipticals: no arms, dust lanes or structure, old stars; spirals: arms, old and young stars; stellar formation in spiral arms; barred-spirals: football or bar shaped nucleus owing to relativistic jet; irregulars: collision, merger, or graviational perturbation by neighboring galaxy; graviational lensing - multiple images of galaxies. Brief history of the Universe.
• Study Guide Quiz 4.
• Apr 6, Thursday: Mid-term exam 4
• Apr 11, Tuesday: Extra-solar planets, recent discoveries; "Hot Jupiters"; techniques for discovering exoplanets; Kepler spacecraft; Habitable "Goldilocks" zone with liquid water. Life in the universe; Definition: DNA - made of common light CHON elements; search for extraterrestrial life - SETI; criteria for existence; organic molecules; Miller-Urey experiment; probability of finding life: Drake equation; physical requirements: solar type stars, number of stars, "intelligence", etc., candidates for life within solar system.
• Apr 13, Thursday: Review
• Apr 18, Tuesday: Lecture by Zhefu Yu
• Apr 20, Thursday: Q&A (via zoom)
• FINAL EXAM: **Note Day & Time** MONDAY, MAY 1 8-9:45 AM, ONLINE ZOOM
• FINAL EXAM: Zoom link has been announced on Carmen starting 7:30-10:15 AM, but exam would start at time above.
• For material since last quiz Q4: last study-guide

Powerpoint files on the homepage and pdf files on Carmen

• Lecture File 1
• Lecture File 2
• Lecture File 3
• Lecture File 4
• Lecture File 5
• Lecture File 6
• Lecture File 7
• Lecture File 8
• Lecture File 9
• Lecture File 10
• Lecture File 11
• Lecture File 12
• Lecture File 13
• Lecture File 14
• Lecture File 15
• Lecture File 16

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Revised: Apr 28, 2023