Transcript Syllabus, Introduction, and Review on Physical Laws

ASTR 113 – 003
Lecture 01
Spring 2006
Jan. 25, 2006
Introduction To Modern Astronomy II
Dr. Jie Zhang
[email protected]
(703)993-1998
ASTR 113 – 003
Spring 2006
Syllabus
• Objectives
– Get to know our universe, across the space and
the time
– Learn the reasoning and critical thinking
• The second course in a two-semester series
• Associated with a Lab (ASTR 114)
• Math helps, algebra and geometry
ASTR 113 – 003
Spring 2006
Syllabus
• One more objective: enjoy
– Milky Way Galaxy (VTS_40_1)
– Galaxy Interaction (VTS_17_1)
– Hubble in 15 years (VTS_37_1)
ASTR 113 – 003
Spring 2006
Syllabus
• Studying Tips
– Before class, reading and preparing yourself
– In class, concentrate on thinking, reasoning and
understanding, but not only memorizing.
• Exam questions are mostly based on your
understanding.
– In class, taking note
– Do not lag behind; hard to catch up later
ASTR 113 – 003
Spring 2006
Syllabus
• Homework & Projects: none (but the lab)
• Three 1-hour-long In-Class Exams
• One Final Exam
• All multiple choice type questions
• Closed book and closed note
• Need ID, Scantron (Bring your own), pencils and
calculators only
ASTR 113 – 003
Spring 2006
Syllabus
• Grading
– Final exam:
40%
– Three IN-CLASS Exam: 60%
• one lowest score is dropped
• No Make-up Exams
– Do not miss the exam
– Do not be late coming to the exam
• No Extra Credit
ASTR 113 – 003
Spring 2006
Honor Code
"George Mason University shares in the tradition of an honor
system that has existed in Virginia since 1842. The Honor Code
is an integral part of university life. On the application for
admission, students sign a statement agreeing to conform to
and uphold the Honor Code. Therefore, students are
responsible for understanding the provisions of the code. In
the spirit of the code, a student's word is a declaration of good
faith acceptable as truth in all academic matters. Therefore,
cheating and attempted cheating, plagiarism, lying, and stealing
of academic work and related materials constitute Honor Code
violations. To maintain an academic community according to
these standards, students and faculty must report all alleged
violations of the Honor Code to the Honor Committee. Any
student who has knowledge of, but does not report, an Honor
Code violation may be accused of lying under the Honor Code."
ASTR 113 – 003
Spring 2006
Contact Information
• Office Hour: Wednesday 2:00 – 4:00 PM
• Other meetings by appointment
• Class website: http://solar.scs.gmu.edu/teaching/ASTR113_2006/index.html
– Presentations will be posted, usually before the class
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Office: Room 111, Science and Technology Building 1
Telephone: (703)993-1998
Fax:
(703)993-1993
E-mail:
[email protected]
Mail-add:
MSN 5C3, George Mason University
ASTR 113 – 003
Spring 2006
Review on Physical Laws
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Kepler’s (1571) Law on Planetary Motion (Chap04)
Newton’s (1642) Law on Motion and Gravity (Chap04)
Maxwell’s (1831) Equation on Electromagnetism (Chap04)
Wien’s (1864) Law on Blackbody Spectrum (Chap05)
Stefan-Boltzmann Law on Blackbody Energy (Chap05)
Kirchoff’s (1824) Law on Spectrum (Chap05)
Bohr’s (1992) Model on Atom (Chap05)
Doppler (1803) Effect (Chap05)
Kepler’s First Law
• Planets orbit the Sun in ellipse with the Sun at one focus
Kepler’s Second Law
•Planets sweep out equal areas in equal times
•Travel faster when closer, slower when further
Kepler’s Third Law
• Orbital Period squared is proportional to semi-major
axis cube
P2 = a3
P = planet’s sidereal period, in years
a = planet’s semimajor axis, in AU
Newton’ three Laws of Motion
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Isaac Newton developed three
principles, called the laws of motion,
that apply to the motions of objects
on Earth as well as in space
These are
1. the law of inertia: a body remains at
rest, or moves in a straight line at a
constant speed, unless acted upon by a
net outside force
2. F = m x a (the force on an object is
directly proportional to its mass and
acceleration)
3. the principle of action and reaction:
whenever one body exerts a force on a
second body, the second body exerts an
equal and opposite force on the first
body
Newton’s Law of Gravitation
F = gravitational force between two objects
m1 = mass of first object
m2 = mass of second object
r = distance between objects
G = universal constant of gravitation
• If the masses are measured in kilograms and the distance between
them in meters, then the force is measured in newtons
• Laboratory experiments have yielded a value for G of
G = 6.67 × 10–11 newton • m2/kg2
Gravitational forces
Maxwell’s Law on Electromagnetism
• Electricity according to Gauss
– relates electricity to electric
charge
• Faraday’s Law
– relates electric fields to magnetic
fields
• Magnetism according to Gauss
– relates magnetism to electricity
• Ampere-Maxwell Law
– relates magnetic field to electricity
Don’t
worry
about
notation
here
The Nature of Light
• In the 1860s, the Scottish mathematician and physicist
James Clerk Maxwell succeeded in describing all the basic
properties of electricity and magnetism in four equations
• This mathematical achievement demonstrated that electric
and magnetic forces are really two aspects of the same
phenomenon, which we now call electromagnetism
The Nature of Light
• light is also called
electromagnetic
radiation
• Visible light falls
in the 400 to 700
nm range
• Stars, galaxies
and other objects
emit light in all
wavelengths
Wavelength and Frequency
Light has properties of both waves
and particles
• Newton thought light was in the form of little packets of energy
called photons and subsequent experiments with blackbody
radiation indicate it has particle-like properties
• Young’s Double-Slit Experiment indicated light behaved as a
wave
• Light has a dual personality; it behaves as a stream of particle
like photons, but each photon has wavelike properties
Photon Energy
E=hν
• Planck’s law relates the energy of
a photon to its frequency or
wavelength
E = energy of a photon
h = Planck’s constant
c = speed of light
 = wavelength of light
ν = frequency of light
• The value of the constant h in this
equation, called Planck’s constant,
has been shown in laboratory
experiments to be
h = 6.625 x 10–34 J s
Wien’s Law
•
Wien’s law states that the dominant wavelength at which a
blackbody emits electromagnetic radiation is inversely proportional
to the Kelvin temperature of the object
Blackbody
• A blackbody is a hypothetical object
that is a perfect absorber of
electromagnetic radiation at all
wavelengths
• Stars closely approximate the
behavior of blackbodies, as do other
hot, dense objects
• The intensities of radiation emitted
at various wavelengths by a
blackbody at a given temperature
are shown by a blackbody curve
Three Temperature Scales
Stefan-Boltzmann Law
• The Stefan-Boltzmann law states that a blackbody radiates
electromagnetic waves with a total energy flux F directly proportional
to the fourth power of the Kelvin temperature T of the object:
F = T4
F: energy flux, in joules per square meters per second
T: object temperature
σ : a constant
Kirchoff’s Laws on Spectrum
• Three kinds of Spectrum
1. Continuous Spectrum
2. Emission Spectrum
3. Absorption Spectrum
Kirchoff’s First Spectral Law
• A hot opaque body, such as a perfect blackbody, or a hot, dense gas
produces a continuous spectrum – a complete rainbow of colors
without any spectral lines.
– digitally like this
Intensity
Wavelength
Kirchoff’s Second Spectral Law
• A hot, transparent gas produces an emission line spectrum – a
series of bright spectral lines against a dark
– or digitally like this
Intensity
Wavelength
Kirchoff’s Third Spectral Law
• A cool, transparent gas in front of a continuous spectrum produces an
absorption line spectrum – a series of dark spectral lines among the
colors of the continuous spectrum
– or digitally like this
Intensity
Wavelength
Kirchhoff’s Laws
Bohr’s Model of Atom
• The nucleus of an atom is surrounded
by electrons that occupy only certain
orbits or energy levels
• When an electron jumps from one
energy level to another, it emits or
absorbs a photon of appropriate
energy (and hence of a specific
wavelength).
• The spectral lines of a particular
element correspond to the various
electron transitions between energy
levels in atoms of that element.
• Bohr’s model of the atom correctly
predicts the wavelengths of
hydrogen’s spectral lines.
Hydrogen alpha (Hα) line
Doppler Effect
Doppler Effect
• Red Shift: The object is moving away from the
observer
• Blue Shift: The object is moving towards the
observer
D/o = v/c
D = wavelength shift
o = wavelength if source is not moving
v = velocity of source
c = speed of light