Astronomy 1143 - Autumn 2017
SYLLABUS: TR 12:45-2:05 PM
Mid-Term Test Dates: Tuesday Sep 11, Tuesday Oct 9, Thursday Nov 1,
Tuesday Nov 20 (40 min duration).
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.
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
- Aug. 21: 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);
the Metric system - used in science and in all
the U.S.; powers of ten in exponents; Universal spatial and temporal history;
- Aug 28: 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
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
- Aug 28 Tuesday: 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
- Aug 30 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".
- Sep 4, 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
- Sep 6, Thursday: Escape velocity, kinetic and potential
energy, orbits, angular momemtum Review Quiz
- Sep 11, Tuesday: First mid-term exam Quiz 1 (40 min) + lecture
- Sep 13, Thursday:
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
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 18, Tuesday:
Quiz 1 grade distribution; Curve +10%.
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 20, 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?
- Sep 25, 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!).
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
Revised: Sep 19, 2018