Transcript Document

Physics 320: Astronomy and
Astrophysics – Lecture XI
Carsten Denker
Physics Department
Center for Solar–Terrestrial Research
NJIT
Lunar Eclipse
November 8th,2003
Eclipsed
Moonlight
from
Connelly's
NJIT
Center for
Solar-Terrestrial
Research
Springs, NC by David
Cortner.
November
12th, 2003
Problem 11.1
L  4 R 2 Te4
Ti

T
Ti

T
1/ 4
1/ 2
1/ 2
 Li   R 
1/ 4  1 

 
   0.71 
  0.979
 0.88 
 L   Ri 
5640 K

 0.977
5770 K
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Problem 11.2
dM
L
4 R 2  Te4
9
14
(a)
 2 

4.26

10
kg/s

6.75

10
M /yr
2
dt
c
c
dM
(b)
 3 1014 M /yr (see Example 11.1)
dt
3

M
3

10
M
10
(c) The life time of the Sun is about 10 years. 

t
1010 yr
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Problem 11.8
d      ds (Eqn.: 9.13)
d
 0,
0
0
 d   ds   
 0,
d   
 
 
1
(with  0,  2 / 3)
 1 : d1  102.6 km (you can see deeper into the Sun)
 2 : d 2  88.9 km
  =1  2  13.7 km
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Physical Processes
in the Solar System
 A Brief
Survey
 Stellar
Evolution
 Planetary Systems
 Tidal
Forces
 The Physics of
Atmospheres
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Protoplanetary
Disks
J.NJIT
Bally
(U. for
Colorado),
H. Throop
U.), NASA
Center
Solar-Terrestrial
Research(SwRI), C.R. O'Dell (Vanderbilt
November
12th, 2003
A Brief Survey
Terrestrial
Jovian
rocky
gas/liquid/ice
Mean orbital distance [AU]
0.39 – 1.52
5.2 – 30.1
Mean surface temperature [K]
200 – 750
75 – 170
Mass [M]
0.055 – 1.0
14.5 – 318
Equatorial Radius [R]
0.38 – 1.0
3.88 – 11.2
Mean density [g cm-3]
3.95 – 5.52
0.69 – 1.64
23.9 h – 243 d
9.8 h – 19.2 h
0–2
8 – 20
no
yes
Basic form
Sidereal rotation period
(equator)
Number of known moons
Ring systems
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Relative Sizes of Planets
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Titius–Bode Rule
Titius–Bode
Distance [AU]
Actual Mean
Distance [AU]
Mercury
(4 + 3  0 ) / 10 = 0.4
0.39
Venus
(4 + 3  20) / 10 = 0.7
0.72
Earth
(4 + 3  21) / 10 = 1.0
1.00
Mars
(4 + 3  22) / 10 = 1.6
1.52
Ceres
(4 + 3  23) / 10 = 2.8
2.77
Jupiter
(4 + 3  24) / 10 = 5.2
5.20
Saturn
(4 + 3  25) / 10 = 10.0
9.54
Uranus
(4 + 3  26) / 10 = 19.6
19.19
Neptune
(4 + 3  27) / 10 = 38.8
30.06
Pluto
(4 + 3  28) / 10 = 77.2
39.53
Planet
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Solar System Inventory
Sun
 Planets
 Moons
 Asteroid belt (2 – 3.5 AU)
 Comets



Kuiper belt (30 AU)
Oort cloud (3000 – 100,000 AU)
Meteoroids, meteor, meteorite,
and meteor shower  asteroid
and comet debris
 Zodiacal light

NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Zodiacal Light
Thousands of stars,
several constellations,
a planet and a comet
all graced the western
horizon over Ujue,
Spain just after sunset
on April 4th, 1997.
Because the picture was
taken with a fisheye lens,
much of the whole night
sky is visible. Comet
Hale-Bopp, with both tails blazing, appears right of center. The
brightest star is Sirius near the edge, well to the left of the constellation
Orion. The red star above the belt of Orion is Betelgeuse, while the red
star near the center is Aldebaran, to the left of the bright Pleiades star
cluster. Many other interesting astronomical objects are visible, e.g.,
the zodiacal light, which is the diffuse triangular glow in the center.
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Origin of the Solar System
Gravitational collapse of the original solar
nebula
 Formation of accretion disk around proto–sun
 Planetesimals (terrestrial planets) and additional
presence of ice (jovian planets)
 More massive planets accumulate extensive
primordial H/He atmospheres
 Jovian planets have local accretion disks
 Capturing of moons
 Cometary nuclei either catapulted into Oort
cloud or completely ejected from solar system

NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Tidal Forces
Mm1
Mm
 dFm 
Fm  G 2  dFm  
dr  2G 3 dr

r
r
 dr 
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Tidal Forces (cont.)
s 2   r  R cos     R sin  
2
 2R

r 1 
cos  
r


neglect terms R 2 / r 2
2
2
GMm
r2
GMm
 2 cos 
s
Center C: FC , x 
FC , y  0
Point P:
FP , y  
FP , x
1
GMm
sin 
2
s
 cos  1  ˆ GMm
F  FP  FC  GMm  2  2  i  2 sin  ˆj
r 
s
 s
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Tidal Forces (cont.)
2R
1
x
cos  and x 1 
1 x
r
1 x
GMm 
 2R
 ˆ
 F
cos  1 
cos    1 i

2
r 
r

 
GMm 
 2R
 ˆ
 2 sin  1 
cos    j
r 
r


cos 
1 and sin 
R sin 
r

GMmR
 F 
2 cos  iˆ  sin  ˆj
3
r
NJIT Center for Solar-Terrestrial Research

Earth’s rotation period is
lengthening at a rate of
0.0016 s/century and the
Moon is drifting away from
Earth by 3 to 4 cm/year.
November 12th, 2003
Physics of Atmospheres
L  4 R2 Teff4 (Stefan-Boltzmann equation)
Under equilibrium conditions, a
planet’s total energy content must
remain constant. Therefore, all of
the energy absorbed by the planet
must be reemitted. If not, the
planet’s temperature would change
with time.
Tp  T 1  a 
1/ 4
R
(a: albedo)
2D
a  0.3  T  255 K  19 C
Greenhouse Effect!
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Exosphere
The region in an atmosphere where the mean free path of the particles
become long enough for them to travel without appreciable collisions
is referred to as exosphere.
3/ 2
 m 
 mv2 / 2 kT
2
nv dv  n 
e
4

v
dv

 2 kT 
(Maxwell  Boltzmann distribution)
NJIT Center for Solar-Terrestrial Research


November 12th, 2003
Exosphere (cont.)
1
3kT
2GM
vrms  vesc with vrms 
and vesc 
6
m
r
1 GM p m
 Tesc 
54 kR p
T  255 K
Tesc (N 2 )  3900 K
TMoon  274 K
Tesc (N 2 )  180 K
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Atmospheric Dissipation and Mixing
H2    H  H
(photodissociation)
Gravitational or
chemical
differentiation
FCoriolis  2m  vr
(Coriolis force)
NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Homework Class Project
Continue improving the PPT presentation.
 Use the abstract from the previous assignment
as a starting point for a PowerPoint presentation.
 The PPT presentation should have between 5
and 10 slides.
 Bring a print-out of the draft version to the next
class as a discussion template for group work
 Homework is due Wednesday November 19th,
2003 at the beginning of the lecture!
 Exhibition name competition!

NJIT Center for Solar-Terrestrial Research
November 12th, 2003
Homework
 Homework
is due Wednesday November
19th, 2003 at the beginning of the lecture!
 Homework assignment: Problems 18.1,
18.5, and 18.7!
 Late homework receives only half the
credit!
 The homework is group homework!
 Homework should be handed in as a text
document!
NJIT Center for Solar-Terrestrial Research
November 12th, 2003