Astronomy 1144 - Autumn 2018
SYLLABUS
TEACHING ASSISTANT: Erica Behrens
Mid-Term Test Dates: Tuesdays: Sep 10, Oct 8, Nov 5, Nov 26
(40 min duration)
We shall be covering topics from a number of chapters 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
textbook.
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.
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
- Aug 20: 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
(Aristotle,Ptolemy),
Geocentric model (Ptolemy) vs. the Heliocentric model (Copernicus).
- Aug 22: 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
the Sky.
- Aug 27: 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).
- Aug 29: TYCHO - the most
famous pre-telescopic astronomer; made careful observations of the orbit
of Mars.
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".
- Sep 3: 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.
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 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.
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.
- Sep 5: Orbiting objects are continuosly 'falling', such as the Moon is
continuously falling towards the Earth, which curves away from it at the
same rate. Escape velocity, kinetic and potential
energy, orbits, angular momemtum.
Like water going down a bathtub
drain, all rotating or revolving object have angular (rotational)
momemtum L = m x v x r (mass times velocity times distance from the
center or axis of rotation); L is conserved, or remains constant;
therefore if r decreases then v must increase, and vice versa; that's
why an ice skater speeds up while spinning when (s)he pulls her/his arms
inwards; Other examples include helicopter rotor, spinning top,
etc.; the axis of a spinning top "wobbles" or "precesses" slowly in a
circle if it is tilted while spinning, instead of falling down;
the precession of the Earth's axis is another example; L acts as a
stabilising quantity, e.g. a gyroscope
(basically a spinning wheel) inside a satellite or spacecraft acts to
stabilise it and point in a certain direction (say towards a star).
Review Quiz 1.
- Sep 10, Tuesday: Mid-Term Exam 1
- Sep 13, Thursday: Ch. 5 - 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);
ach photon has a definite wavelength and hence 'color'.
- Sep 17, Tuesday: ATOMS and SPECTRA - Quantum Theory: The
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
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.
ydrogen -
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.
- Sep 19, Thursday: 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); 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?
Quiz 1 grade distribution; Curve +5%.
- Sep 24, Tuesday: 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!).
- Sep 26, Thursday: 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: negative hydrogen ion layer absorbs visible to infrared
radiation; than chromosphere, transition region and the corona; flares
and mass ejections driven by magnetic activity.
- Oct 1, 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.
- Oct 3, Thursday: 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
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.
Mass is the most important quantity that determines the size,
luminosity, temperature and lifetime of a star. Hot, cool,
high luminosity and low luminosity stars are located on the left, right,
top and bottom of the HR diagram respectively.
M(star) ~ L^(3.5), i.e. the star produces energy L nearly as power of 4
with increasing mass; therefore massive stars have shorter lifetimes
since they burn up faster.
- Oct 8, Tuesday: Mid-term Exam 2 Review Quiz 2.
- Oct 15, Tuesday: 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.
- Oct 17, Thursday: 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
further into a BH because even neutron degeneracy pressure is unable to
withstand gravity. Binay Stars: Slighlty more than half of stellar
systems
are binary, rather than singly like our Sun; enable determination of
masses using Kepler's and Newton's laws.
Distance and luminosity; difference between apparent brightness and
absolute luminosity is related to distance; H-R diagram can be used to
determine distances; parallax; transvere and radial
velocity; stellar parameters; binary stars: visual, spectroscopic, and
eclipsing binaries;determination of stellar masses through Keplerian
orbits and Newton's laws of motion and gravitation; proper motion,
distances and catalogs of stars.
Quiz 2 grade distribution; Curve +3%.
- Oct 22, Tuesday: 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; atomic ions
[OII], [OIII], [SII] and their "forbidden" (low probability) lines
cover visible spectrum from blue to red,
and provide temperature/density diagnostics;
lifetimes and birth of stars; protostars and proto-planetray disks;
arrival on the
Main Sequence in H-burning stage; stellar structure and interior zones.
- Oct 24, Thursday:
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.
- Oct 29, Tuesday: 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.
- Oct 31, 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.
- Nov 5, Tuesday: Mid-term Exam 3 Review Quiz 3.
- Nov 7, Thursday: 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.
- Nov 12, Tuessday: 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.
- Nov 14, Thursday: 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 ~ 4 million
M(Sun).
Quiz 3 grade distribution; Curve +5%.
- Nov 19, Tuesday: 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; gravitational lensing and multiple images.
- Nov 21, Thursday: 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.
- Nov 26, Tuesday: Mid-term Exam 4 Review
Quiz 4.
- Dec 3, Tuesday: 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.
- Dec 4, Wednesday: Extended office hours 4-6 PM.
- Final Review; Ignore sections
on Life and Extra-solar planets.
Quiz 4 grade distribution; Curve +5%.
- Dec 9, Monday, FINAL EXAM 12:00-1:45 PM (HERE). Good Luck!
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
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Revised: Dec 4, 2019
