Physics 320: Astronomy and Astrophysics – Lecture XI

NJIT

Physics 320: Astronomy and Astrophysics – Lecture XI

Carsten Denker

Physics DepartmentCenter for Solar–Terrestrial Research

November 12th, 2003NJIT Center for Solar-Terrestrial Research

Lunar Eclipse November 8th,2003

Eclipsed Moonlight from Connelly's Springs, NC by David Cortner.


Problem 11.1

2 4

1/ 4 1/ 2 1/ 21/ 4

4

10.71

0.88

5640 K

57

0.979

7 7

K9

00. 7

e

i i

i

i

L R T

RT L

T L R

T

T


Problem 11.2

2 49 14

2 2

14

310

10

4(a) 4.26 10 kg/s 6.75 10 M /yr

(b) 3 10 M /yr (see Example 11.1)

3 10 M(c) The life time of the Sun is about 10 years.

10 yr

edM L R T

dt c cdM

dt

M

t


Problem 11.8

0, 0,0,0 0

1 1

2 2

1 2

(Eqn.: 9.13)

1 (with 2 / 3)

: 102.6 km (you can see deeper into the Sun)

: 88.9 km

= 13.7 km

d

d ds

d ds d

d

d


Physical Processes in the Solar System

A Brief Survey Stellar Evolution Planetary Systems

Tidal ForcesThe Physics of

Atmospheres


Protoplanetary Disks

J. Bally (U. Colorado), H. Throop (SwRI), C.R. O'Dell (Vanderbilt U.), NASA


A Brief Survey

Terrestrial Jovian

Basic form 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

Sidereal rotation period (equator)

23.9 h – 243 d 9.8 h – 19.2 h

Number of known moons

0 – 2 8 – 20

Ring systems no yes


Relative Sizes of Planets


Titius–Bode Rule

Planet 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


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


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.

Zodiacal Light


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


Tidal Forces

12 3

2mm m

dFMm MmF G dF dr G dr

r dr r


Tidal Forces (cont.)

, ,2

, ,2 2

Center : 0

Point : cos sin

C x C y

P x P y

GMmC F F

rGMm GMm

P F Fs s

2 2 2

cos 1 ˆ ˆsinP C

GMmF F F GMm i j

s r s

2 22

2

2 2

cos sin

21 cos

neglect terms / 1

s r R R

Rr

r

R r


Tidal Forces (cont.)

2

2

2 1cos and 1 1

1

2 ˆcos 1 cos 1

2 ˆsin 1 cos

Rx x x

r x

GMm RF i

r r

GMm Rj

r r

3

sincos 1 and sin

ˆ ˆ2cos sin

R

rGMmR

F i jr

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.


Physics of Atmospheres2 4

eff (Stefan-Boltzmann equation4 )L R T

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.

1/ 4 ( : albe1

2do)p

RT T a a

D

0.3 255 K 19

Greenhouse Effect!

Ca T


ExosphereThe 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.

23/ 2

/ 2 24

(Maxwell Boltzmann distribution)

2mv kT

v

mn dv n e v dv

kT


Exosphere (cont.)

rms esc rms esc

1 3 2 with and

6

1

54p

escp

kT GMv v v v

m rGM m

TkR

esc 2

Moon

esc 2

255 K

(N ) 3900 K

274 K

(N ) 180 K

T

T

T

T


Atmospheric Dissipation and Mixing

2

(photodissociation)

H H H

Coriolis

(Coriolis for

2

ce)rF m v

Gravitational or chemical differentiation


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!


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!

Documents

Physics 320: Astronomy and Astrophysics – Lecture XI