Astronomy 1144 - Spring 2015
TEACHING ASSISTANT: Carl Coker
Mid-Term Test Dates: Thursdays Jan 29, Feb 19, Mar 12, Apr 9
We shall be covering topics from Chapters 3-5 and 16 - 28 in the textbook.
However, we will not be following the textbook exactly, and many
topics therein will not be covered in class. You should
know the material we do cover in class, and read corresponding material in the
The exam questions will be largely from material covered in class.
The daily topics listed below cover only the main points. Make sure to
read your notes and the corresponding material in the Textbook.
- Jan 13: Syllabus; Overview: stars and galaxies, stellar properties and evolution. 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.
Metric system is normally used in science and in all countries except
the U.S.; powers of ten in exponents; 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;
science and religion: faith vs. inquiry; ancient astronomy; use of
Geometry by the Greeks, belief in the Geocentric system
Geocentric model (Ptolemy) vs. the Heliocentric model (Copernicus).
- Jan 15: The distance scale, linear and 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.
The Celestial Sphere - stars 'fixed' in the
Sky as a globe; the distance scale; physical and angular distances and sizes;
distance measures in astronomy are the AU and the Light
year (LY); another distance unit is based on the method of parallax -
the 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.
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
- Jan 20: 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
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
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.
- Jan 22: 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".
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
Newton's LAWS OF MOTION (i) Inertia and mass, (ii)
F = ma, (iii) action = reaction;
acceleration a = velocity /time; velocity is speed in a given
direction; requires force to change either speed or direction;
Acceleration a = velocity /time; velocity is speed in a given
direction; requires force to change either speed or direction;
momemtum is mass x velocity (mv), which is conserved before and after an
even; conservation of momemtum (m*v) and the third law of motion.
Newton's Laws (Contd.) - Weight is the force of
gravity on mass m; acceleration due to gravity;
application of (i) and (ii) and the law of
Gravitation gives W (weight) = mg, where g is the grav. acceleration;
g = 9.8 m/sec-squared (m/sec/sec) = 32 ft/sec/sec; constant for all
falling masses (hence Galileo's observation that 'all things fall at the
same rate'); in fact Galileo used inclined planes to slow down the
acceleration and measure the times accurately, instead of relying on
freely falling objects with little discernible difference to the human
eye; Escape veloctiy' is the
ity needed to escape the gravity of the Earth = 11 Km/sec;
Orbiting objects are continuosly 'falling', such as the Moon is
continuously falling towards the Earth, which curves away from it at the
- Jan 27: Review Quiz 1.
Stars and Galaxies - Introduction
- Jan 29: Quiz 1 (first 40 min) and lecture: Ch. 5 - Light and matter,
spectroscopy, color (wavelength), electromagnetic spectrum - Gamma-Rays to Radio waves in increasing wavelength.
- Feb 3: 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 light are 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';
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 6563 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.
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.
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.
- Feb 5: Quiz 1 grade distribution; Curve +4%.
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
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); indicates uniform and isotropic expansion; however, recent re
sults show accelerating expansion --> Dark Energy ? Rotation curves of galaxies are flat, rather than decreasing with radius --> Dark Matter?
- Feb 10: 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 velocity; the General Theory of
Relativity deals with acceleration; 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 12: Stars - Properties and structure of the Sun; State of matter:
99.9% of matter in the Universe is in plasma state (free
electrons, protons, and ions); 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.
- Feb 17: 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
lines (e.g. A stars have strong H lines); stellar luminosity classes: I-V;
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.
Review Quiz 2.
- Feb 19: Quiz 2. 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-mass stars: M < 3M(Sun) --> Red Giants --> White Dwarfs;
High-mass stars: M > 3M(Sun) --> Neutron Stars; M > 8-10 M(Sun) --> Black Hole;
determined by Chandrasekhar Limit = 1.44 M(Sun), mass where electron pressure balances gravity; when M (core) > 1.44 M(Sun), the core
gravitationally collapses into neutron star or BH.
- Feb 24: 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; heavier mass stars with M(Core) > 3 M(sun) collapse even furhter into a BH because even neutron degeneracy pressure is unable to withstand gravity.
- Feb 26: Distance and luminosity; parallax; transvere and radial velocity; sstellar parameters; binary stars: visual, spectroscopic, and eclipsing binaries;determination of stellar masses through Keplerian orbits and Newton's laws of motion and gravitation; distribution of stars on the HR diagram.
- Mar 3: Nebulae as stellar nurseries; masses and stellar types at birth;
interstellar medium (ISM); nebular types; radiation extinction and reddening due to dust; blue light scatters out of line of sight more than red --> reddening correction needed; nebular spectra; [OII], [OIII], [SII] "forbidden" lines; cover visible spectrum from blue to red and provide temperature/density diagnostics;
birth of stars; protostars and proto-planetray disks; arrival on the Main Sequence in H-burning stage; stellar structure and interior zones.
- Mar 5: Evolution of low-mass stars on the HR diagram; H --> He fusion in the core produces helium in the core;
the star expands as the H-burning shell moves outward in the core and
the star becomes more luminous Red Giant; away from the MS turn-off
right and up;
the inert helium core contracts until T ~ 100 million K
when explosive He
burning occurs (helium flash); star now moves leftward on the HR diagram with incerasing temperature;
triple-alpha reaction produces carbron-dominated core with some oxygen; as the outer envelope of the star is ejected the central stellar
core becomes exposed and increasingly luminouss; star moves up the HR diagram rapidly along the Asymptotic Giant Branch (AGB); ages of stars determined from stars in a cluster with different masses; arrive and turn-off from the MS at different ages in their lifetimes --> isochrones.
Evolution of high-mass stars: Evolution and nucleosynthesis in M > M(Sun) stars; CNO cycle is more efficient than p-p reactions at hydrogen burning; evolution of supergiants from the MS at relatively constant luminosity by temperature variations; fusion of heavy elements beyond T > 600 million K; red and blur supergiant phases; of the order of a million years to crisscross the HR diagram; onion-skin model of elements in massive star interiors as they evolve up to iron core; core collapse leads to supernova or black hole.
- Mar 10: 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 12: Quiz 3: ******* will include material covered on Feb 17
and thereafter, particularly the H-R diagram, as well as Hubble's law
covered on Feb 5 *******. Review Quiz 3
Note that the Quiz 3 review is mistakenly labeled "Quiz 2 Review". No
office hours today and no class after quiz.
- Mar 13-23, Spring Break.
- Mar 24: Q3 Curve +4%. Stellar formation; Pre-Main-Sequence stars; Hayashi track; Approach time to Zero-Age-Main-Sequence; young stellar clusters; brown dwarfs (failed stars); massive stars - Cepheid variables; novae and supernovae.
- Mar 26: Summary of stellar formation, evolution, and end of stars. Types of supernovae - Type 1a, 1b, 1c and Type II; SN 1987A, Crab SN and pulsar; neutron stars and black holes: radio pulsars; structure of neutron stars and black holes.
- Mar 31: General Relativity and black holes; Milky Way:
Galactic structure and dynamics; spiral structure; rotation curves and dark matter; Sgr A - suppermassive black hole at the Center ~ 3 million M(Sun).
- April 2: Stellar populations and ages; Galaxy types: ellipticals, spirals and barred spirals, Irregulars; Hubble tuning-fork diagram; galactic collisions;
clusters of galaxies; local group around Milky Way; cosmological distance ladder(revisited); gravitational lensing and multiple images.
- April 7: Active galactic nuclei (AGN) and quasars; high redshift quasars;
AGN spectra is non-stellar (non-thermal or non-blackbody); roughly constant radiation flux at all wavelengths; radio-loud and radio-quiet fluxes; jets of relativistic (high-velocity) particles emit synchrotron radiation at radio wavelenths;radio lobes as endpoints of jets; supermassive black hole paradigm of AGN and quasars; evolutionary sequence of galaxies.
- April 9:Review Quiz 4. Quiz 4.
- April 14: Large-scale structure and cosmology; Three pillars of Big Bang
cosmology supported by observations:
Redshift, CMB, primordial abundances; matter and energy density;
observed total (matter + energy) density and critical density 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; 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; Radiation and matter dominated phases of the universe; recombination epoch -- atomic formation and radiation matter decoupling; large-scale structure: galaxies, clusters of galaxies, superclusters, voids, etc.; galaxy "seeds" with inflations; 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;
Lyman-alpha "forests" due to absorption of distant quasar light by H-clouds
at varying redshifts.
- April 16: Extra-solar planets (lecture by Carl Coker).
- April 21: Life - Life in the universe; Definition: DNA;
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, etc., candidates within solar system.
- April 23: No class but extended office hours 12:30-2:00 PM and
- Final exam study guide
- May 1: FINAL EXAM, Friday, 8:00-9:45 PM (Here). Please fill out
- May 5: Final exam curve 4%. Course grades posted. Final exams
can be picked up from the TA Carl Stoker this week.
POWERPOINT LECTURE FILES
Please note that this material is posted as an aid to,
not as a substitute for, class lectures. Any questions should be
preferably addressed in class (not by email).
- 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: May 5, 2015