Transcript Solar system: 9 light hours diameter

Solar system: 9 light hours diameter
Spiral galaxy: 80,000 light years diameter
Coma cluster of galaxies: 2.5 million light years across
Survey of distant galaxies: 5 to 9 billion light-years away
Cosmic Microwave Background Radiation (after-glow from
the Big Bang) - edge of the observable Universe:
14 billion light years away
General Astrophysical Concepts:
Astronomical length scales and time scales
First principles of cosmology
• The universe is: (a) HOMOGENOUS
(b) ISOTROPIC
• Homogeneity implies isotropy,
• But isotropy does NOT imply homogeneity
Kepler's laws of motion
• (1) Orbits of planets follow ELLIPSES with the Sun at one
of the two foci
• (2) Equal areas are swept out in equal intervals of time
• (3) P2 α R3 or P2 = C R3 / M
where P is the period of the orbit, R is the `radius' of
the orbit, and M is the mass of the central object (Sun)
Elliptical path/orbit
followed by
planet
Sun
+
◦
Sample Pop-quiz
Which of the following statements is TRUE:
A. When galaxies collide, it is very common for
stars to smash into each other
B. Primordial density fluctuations grow under the
influence of the electromagnetic force
C. Large galaxies are assembled by the merging of
smaller galaxies
D. The furthest galaxies we can see from Earth are
100 billion light years away
Forces of Nature
• Newton's Laws of Motion
• Inverse square law of forces
• Fundamental forces (4)
(1) Gravitational force
Example:
falling
apple
(2) Electromagnetic force
Example:
horseshoe
magnet
(3) Weak nuclear force
Example:
β-decay or
top bottom quark
(4) Strong nuclear force
Example:
force that binds
protons & neutrons
in atomic nuclei
The Milky Way and Other Galaxies Like It
• Overview of its constituents
• Dynamics (and mass) of a typical spiral galaxy:
The Milky Way
• Application of Kepler's third law (math application):
- The Solar System and Milky Way compared
- How many stars does the Milky Way contain?
The Detailed Structure of a Spiral Galaxy
Electromagnetic Radiation
• Propagation of Energy in the Form of Oscillating Electric
and Magnetic Fields
• Speed of propagation (in vacuum): c = 300,000 km/s
• Frequency ν: number of oscillations per second
[Unit of frequency: s-1 or Hertz (Hz)]
• Wavelength λ: distance traveled during one oscillation
[Unit of wavelength: meter (m), Angstrom (1 Å= 10-10 m)]
• c = λν or λ= c/ν or ν = c/λ
[ν & λ are inversely proportional to each other]
Electromagnetic Spectrum
• Progression of frequency or wavelength
Radio, millimeter, sub-millimeter, microwave, infrared,
optical, ultraviolet, X-ray, gamma rays
• Optical/visible white light spectrum (rainbow colors):
Red Orange Yellow Green Blue Indigo Violet
[Order of decreasing wavelength, increasing frequency]
Atmospheric Windows
• Optical, [sub-millimeter], millimeter, and radio
wavelengths
• Impact on astronomy (and on human evolution!)
Sample Pop-quiz
Which of the following statements is FALSE:
A. When galaxies collide, it is very common for
stars to smash into each other
B. Primordial density fluctuations “grow” under the
influence of the gravitational force
C. Large galaxies are assembled by the merging of
smaller galaxies
D. The furthest galaxies we can see from Earth are
about 10 billion light years away
Black Body Radiation
• Perfect emitter of radiation; perfect absorber of radiation
• Energy radiated per second depends on temperature:
L = AσT4 or L = 4πR2σT4 (sphere of radius R)
where: L = luminosity (in erg/s); A = surface area
σ = Stefan's constant; T = temperature (in Kelvin = °C + 273)
• `Quality' of radiation (ν or λ or color) depends on the
black body temperature (Wien's law): λpeakT = constant
(λpeak is inversely proportional to T)
Black Body Radiation
Wave-Particle Duality
• Radiation consists of energy
bundles (quanta) called photons
• Energy of each photon: E = hν
where: h = Planck's constant,
ν = frequency of radiation
[Energy of each photon depends
on `color' (λ, ν) of radiation]
• The more luminous a source of
radiation, the more photons it
emits per second
Atomic Energy Levels
• An atom in Quantum Mechanics; discrete energy levels
• Transitions between levels: emission & absorption lines
Continuum, Emission Line, and
Absorption Line Radiation