Transcript Lecture 10

ASTR 1200
Announcements
Exam #1 in class, next Tuesday, October 7
Have posted review sheet and sample exam
Help room: Mondays 3-5,Duane G2B90
Review Today
Josh review/help session today after class?
Website
http://casa.colorado.edu/~wcash/APS1200/APS1200.html
Structure of the Exam
Closed book.
Calculators strongly recommended. (Check batteries!)
Pencils are a good idea for the calculations. (but not necessary)
Formulae and constants you need will be provided.
Just like the sample exam.
Will not be a test of time. Should be finished in under one hour.
But will have full 75minutes to complete it.
How to Study
Knowledge
Facts. Multiple Choice
Fast. Do these first.
Conceptual
How things work. Written Answers
Calculations
Identify and use the formulas.
These take longer. Do them last.
Homeworks
Redo them.
Do additional exercises.
Lecture Notes
Go through each powerpoint slide and make certain you understand.
Textbook
Background reading of for explanation of individual points.
Test yourself to identify weak areas using review sheet and sample exam.
Material Covered
Drakes Equation and prevalence of Life in the Universe
Scientific Notation
Sizes of things
Formation of Solar System
Position, velocity, acceleration
Newton’s Laws
Orbits
Escape Velocity
Surface Gravity
Orbital Period
Structure of Sun
Nuclear Processes
Solar Activity
Material Covered
Our place in the galaxy
Light years and parsecs
Parallax
Proper Motion
Brightness
Magnitudes and Absolute Magnitudes
Concept only from here on:
Electromagnetic Spectrum and its parts
Spectroscopy
Spectral Types
The Spectral Types
Stars of
Orion's Belt
>30,000
K
Lines of ionized helium, weak
hydrogen lines
<97 nm
(ultraviolet)*
B
Rigel
30,000
K10,000
K
Lines of neutral helium,
moderate hydrogen lines
97-290 nm
(ultraviolet)*
A
Sirius
10,000
K-7,500
K
Very strong hydrogen lines
290-390 nm
(violet)*
F
Polaris
7,500 K6,000 K
Moderate hydrogen lines,
moderate lines of ionized
calcium
390-480 nm
(blue)*
G
Sun, Alpha
Centauri A
6,000 K5,000 K
Weak hydrogen lines, strong
lines of ionized calcium
480-580 nm
(yellow)
K
Arcturus
5,000 K3,500 K
Lines of neutral and singly
ionized metals, some
molecules
580-830 nm
(red)
M
Betelgeuse,
Proxima
Centauri
<3,500
K
Molecular lines strong
>830 nm
(infrared)
O
*All stars above 6,000 K look more or less white to the human eye
because they emit plenty of radiation at all visible wavelengths.
The H-R Diagram
Plot of Brightness vs Temperature
-5
Giants
Rigel
Capella
Brightness
0
Sirius
Procyon
Sun
+5
Main Sequence
a Cen B
White Dwarfs
+10
Sirius B
Prox Cen
+15
O
B
A
F
G
Spectral Type
K
M
The H-R Diagram
The Main Sequence
Stars Differ By:
Mass
Age
Composition
Nothing else!
And composition doesn’t vary
Age and Mass only.
Those on main sequence are all
burning H so age drops out.
MS is function of MASS only!!!
Full, Artistic H-R
As mass of
MS star increases,
both R and T
increase
increasing
size
sAT4
T constant
on any vertical
line
Newly Formed Star
-5
Giants
Rigel
Capella
0
M
Sirius
Protostar
Procyon
Sun
+5
Main Sequence
Then sits while
burning H
a Cen B
White Dwarfs
+10
Sirius B
Prox Cen
+15
O
B
A
F
G
Spectral Type
K
Large,
Low T.
Settles down
to MS
M
MS Lifetime
What determines amount of time a star stays on Main Sequence?
Just like a kerosene heater: Amount of fuel and rate of burn.
More Mass = More Fuel
More Luminosity = Greater Burn Rate
We can scale from the Sun: M = 1M
L = 1L
Sun lasts 1010 years
M
MSLife  10
L
10
M in solar masses
L in solar luminosities
Some Lifetimes
Sun
Sirius
Prox Cen
Rigel
Mass
Luminosity
Lifetime in Billion Years
1
2
.4
8
1
10
.001
10,000
10
2
4000
.008
Dinky little stars like Prox Cen will last trillions of years
Huge stars like Rigel are gone in a few million
There aren’t many large stars out there, because they don’t last.
10,000 O stars of the 100,000,000,000 Milky Way stars