Transcript HNRS 227 Lecture #2 Chapters 2 and 3

HNRS 227 Lecture #15-17
Chapters 16, 17 and 18
The Universe and Solar System
presented by Prof. Geller
17,22,24 October 2002
Key Points of Chapter 16
Historical Views (also in Chapter 17)
geocentric model of the universe
Ptolemaic Model
heliocentric model of the universe
Copernican Model
Coordinate Systems
Local Horizon System
altitude, azimuth
Celestial Coordinate System
right ascension, declination
Key Points of Chapter 16
Measurements
angular degrees
1 degree = 60 minutes = 3600 seconds
hour-angle
one hour is 15 degrees of arc
light year
distance traveled by light in a year
Astronomical Unit (AU)
mean distance of Earth to Sun
Key Points of Chapter 16
Main Sequence Stars
core, radiation zone, convection zone,
photosphere
Magnitude Scale
log scale
lower value brighter (x 2.5) than higher value
absolute versus apparent
absolute is magnitude at 10 parsecs
Key Points of Chapter 16
Temperature of stars
Wien’s Law
spectral classes based upon temperature
not linear scale
H-R Diagram
temperature versus absolute brightness
following the evolution of stars
The Hertzsprung-Russell (HR) Diagram
The Life Story of Stars
 Gravity squeezes
 Pressure forces resist
 Kinetic pressure of hot gases
 Repulsion from Pauli exclusion
principle for electrons - white dwarf
 Repulsion from Pauli exclusion
principle for neutrons - neutron star
 None equal to gravity - black hole
 Energy loss decreases
pressure
 Energy generation replaces
losses
 Star is “dead” when energy
generation stops
 White dwarf, neutron star, black hole
Luminosity
Surface
Gravity
Weight of outer layers
Gas
Pressure
Thermal
Energy
Center
Helium burning
Post Main
Sequence
Evolution
Heium “Burning”
4He
2
+ 4He2  8Be4
8Be
4
+ 4He2 
12C
12C
+ 4He2 
16C
6
6
8
+ 
+ 
Evolution from Giants to Dwarfs
Stellar Evolution by Mass
Main sequence stars
Supergiants
Giants
Helium flash
C detonation
Heavy nuclei fusion
Supernovae
Planetary nebulae
Black holes
Ns
White dwarfs
100
40
10
4.0
Mass (MSun = 1)
1.0
0.4
0.1
25 Msun Star Evolution
S ta g e
Hydrogen burning
Central
Temperature
(K )
7
4 x 10
Helium burning
2 x 10
8
7 x 10
2
5 x10 year
Carbon burning
6 x 10
8
2 x 10
5
600 year
Neon burning
1.2 x 10
9
4 x 10
6
1 year
Oxygen burning
1.5 x 10
9
1 x 10
7
6 months
Silicon burning
2.7 x 10
9
3 x 10
7
1 day
Core collapse
5.4 x 10
9
3 x 10
9
0.2 seconds
Core bounce
2.3 x 10
10
4 x 10
14
milliseconds
Explosion
About 10
9
Central
Density
3
(g/cm )
5
Varies
Duration of
stage
6
7 x10 year
5
10 seconds
Key Points of Chapter 16
Galaxies
our own Milky Way
different types
elliptical, spiral, barred spiral
Hubble’s Law
Cosmology
Recall the Doppler Shift
A change in measured frequency caused
by the motion of the observer or the
source
classical example of pitch of train coming
towards you and moving away
Hubble’s Law
The further away a galaxy is, the greater
its recessional velocity and the greater its
spectral red shift
Hubble’s Conculsion
From Hubble’s Law we can calculate a
time in the past when universe was a
point
Big bang occurred about 15 billion years
ago
big bang first proposed by George Gamow
based upon such evidence
big bang named by antagonist Fred Hoyle
who preferred the steady-state model
Key Points of Chapter 17
Geocentric solar system
Ptolemaic model
Heliocentric solar system
Copernican model
Kepler’s Laws of Planetary Motion
Origin of Solar System
Overview of Planets
Kepler’s Laws of Planetary Motion
Kepler’s First Law of Planetary Motion
planets orbit sun in an ellipse with sun at one
foci
Kepler’s Second Law of Planetary Motion
planets sweep out equal areas in equal times
travel faster when closer, slower when farther
Kepler’s Third Law of Planetary Motion
orbital period squared is proportional to
semi-major axis cubed
• P2 = a3
Planetary Observations
Planets formed at same time as Sun
Planetary and satellite/ring systems are
similar to remnants of dusty disks such as
that seen about stars being born
Planet composition dependent upon
where it formed in solar system
Nebular Condensation
(protoplanet) Model
Most remnant heat from collapse retained
near center
After sun ignites, remaining dust reaches
an equilibrium temperature
Different densities of the planets are
explained by condensation temperatures
Nebular dust temperature increases to
center of nebula
Nebular Condensation Physics
Energy absorbed per unit area from sun =
energy emitted as thermal radiator
Solar Flux = Lum (Sun) / 4 x distance2
Flux emitted = constant x T4 [Stefan-Boltzmann]
Concluding from above yields
T = constant / distance0.5
Nebular Condensation
Chemistry
Molecule
H2
H2O
CH4
NH3
FeSO4
SiO4
Freezing Point Distance from
Center
>100 AU
10 K
>10 AU
273 K
>35 AU
35 K
>8 AU
190 K
>1 AU
700 K
>0.5 AU
1000 K
Key Points of Chapter 18
Earth’s Motions
revolution
about Sun
rotation
on its axis
Reason for the seasons
tilt of the Earth’s axis
Measuring time
hours, minutes, seconds
Key Points of Chapter 18
The Moon
phases of the Moon
Eclipses
lunar
solar
Tidal Effects