Astronomy 1143 - Autumn 2017
SYLLABUS: TR 12:45-2:05 PM
Mid-Term Test Dates: Tuesdays - Sep 12, Oct 10, Oct 31, Nov 21
(40 min duration, followed by lecture)
The tests are on the material covered in class during the given mid-term
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
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.
- Aug. 22: 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
Geocentric model (Ptolemy) vs. the Heliocentric model (Copernicus).
- Aug 24: The Metric system; Universal spatial and temporal history; observational astronomy; he distance scale; angular size and parallax;
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.
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 (next lecture).
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.
- Aug. 29: 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. 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;
- Aug 31: 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
- Sep 5, Tuesday: 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".
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
- Sep 7, Thursday: 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
veloity 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
same rate. In class review test 1. i
Stude Guide Quiz 1
- Sep 12, Tuesday: Quiz 1, 40 min + Class
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).
- Sep 14, Thursday: Quiz 1 Grade
Distribution; Curve +5%; Exam sheets will be sorted and handed back
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 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'.
- Sep 19, Tuesday: 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.
- Sep 21, Thursday: Continuous, absorption, and emission spectra from
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.
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); Cosmic Microwave
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?
- Homework #1
This homework is optional but recommended; solutions will be posted
after all topics have been covered. It will not be graded.
- Sep 26, Tuesday: Einstein's Theory of RELATIVITY.
First Postulate - speed of light 'c' is a universal
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!).
- Sep 28, 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
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%.
- Oct 3: Stellar Classification -stars are classified according to
color and temperature. Hertzsprung-Russell
(HR) diagram of luminosity L vs. temperature T; stellar classification
O,B,F,G,K,M,L - ranging in T ~ 50,000 - 1000 K; numeral subdivision
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.
- Oct 5: 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. Stude Guide Quiz 2
Hoemwork 1 Solutions
- Oct 10: Quiz 2, no class.
Quiz 2 Grade Distribution; Curve +5%;
Exam sheets will be sorted and handed back on Tuesday.
- Oct 17, Tuesday: Gravitational collapse is balanced by
electro-electron repulsion; Chandrasekhar Limit = 1.44 M(Sun), mass where
electron 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
- Oct 19, Thursday: Distance and luminosity; apparent and absolute
magnitudes for measuring brightness;
distance modulus (m-M) = 5 - 5 logd - 5; absolute luminosity at d =
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
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.
Homework #2 .
- Oct 24, 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.
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.
Telescopes (Courtesy: Ralph Spitzen) .
- Oct 26, Thursday: Stellar fuel; nuclear energy and reactions;
nucleosynthesisof elements; stellar evolution; evolutionary phases and
tracks on the HR-diagram; supernovae and production of heavy elements;
Review Quiz 3
- Oct 31, Tuesday: Quiz 3, No class after quiz . Q3 will include
from previous period, including HR diagram and material not quite
covered on Oct 5 above about stellar evolution and nucleosynthesis.
Quiz 3 Grade Distribution; Curve +7%;
- Nov 2, Thursday: 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. Cosmological distance ladder:
trignometric parallax, spectroscopic parallax, Cepheid variables,
Supernovae Type Ia.
- Nov. 7, Tuesday: 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
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
General Relativity and Friedmann Equations; value of critical density;
Omega = 1 implies dark matter and dark energy constitute about 95% of
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
Einstein and Friedmann equations of General
Radiation and matter dominated phases of the universe; recombination
epoch -- atomic formation and radiation matter decoupling.
- Nov 14, Tuesday: Large-scale structure: stars, galaxies, galaxy
clusters of galaxies, superclusters, voids, etc.; galaxy "seeds" with
CMB anisotropy due to matter distortions are
small angular scales; formation of first stars and galaxies during
end of 'dark ages' that followed the recombination epoch.
Homework #3 ,
- Nov 16, Thursday: Lyman-alpha "forests" due to absorption of
distant quasar light by intervening H-clouds at varying redshifts.
Milky Way and Galactic structure; Q4 Review.
Review Quiz 4
- Nov 21, Tuesday: Quiz 4, no class.
- Quiz 4 Grade Distribution; Curve +7%.
- Nov 28, Tuesday: 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.
- Nov 30, Thursday: History of the Universe: big questions.
Life in the universe; Definition: DNA - made of common light CHON
search for extraterrestrial life - SETI;
criteria for existence; organic molecules; Miller-Urey experiment;
f finding life: Drake equation; physical requirements: solar type stars,
of stars, "intelligence", etc., candidates for life within solar system.
Extra-solar planets, recent discoveries; "Hot Jupiters";
techniques for discovering exoplanets; Kepler spacecraft; Habitable
"Goldilocks" zone with liquid water.
- Review Final
- Dec 5, Tuesday: No class, extended office hours 3:30-5:30 PM.
- Dec 12, Tuesday: FINAL EXAM 2:00-3:45 PM (Here).
- Final Grade Distribution; Final Curve +4%,
plus overall curve +2%.
- **************** URGENT ERROR *****************
There was an error in the computer program and the grades for those
exceeding 100% including the curve have been incorrectly assigned. Will
POWERPOINT LECTURE FILES
Owing to possible last-minute changes, check the powerpoint files
below AFTER the lectures.
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
- File 9 is not needed, material already covered
- Lecture File 9
- Lecture File 10
- Lecture File 11
- Lecture File 12
- Lecture File 13
- Lecture File 14
- Lecture File 15
- Lecture File 16
Revised: Dec 13, 2017