ASTR 1200Announcements

Websitehttp://casa.colorado.edu/~wcash/APS1200/APS1200.html

Exam #1 in class, next Tuesday, October 7

Have posted review sheet and sample examHelp room: Mondays 3-5,Duane G2B90

Review TodayJosh review/help session today after class?

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 StudyKnowledge

Facts. Multiple ChoiceFast. Do these first.

ConceptualHow things work. Written Answers

CalculationsIdentify and use the formulas.These take longer. Do them last.

HomeworksRedo them. Do additional exercises.

Lecture NotesGo through each powerpoint slide and make certain you understand.

TextbookBackground 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 UniverseScientific NotationSizes of thingsFormation of Solar SystemPosition, velocity, accelerationNewton’s LawsOrbitsEscape VelocitySurface GravityOrbital PeriodStructure of SunNuclear ProcessesSolar Activity

Material Covered

Our place in the galaxyLight years and parsecsParallaxProper MotionBrightnessMagnitudes and Absolute Magnitudes

Concept only from here on:

Electromagnetic Spectrum and its partsSpectroscopySpectral Types

The Spectral Types

OStars of Orion's Belt

>30,000 K

Lines of ionized helium, weak hydrogen lines

<97 nm (ultraviolet)*

B Rigel

30,000 K-10,000 K

Lines of neutral helium, moderate hydrogen lines

97-290 nm (ultraviolet)*

A Sirius10,000 K-7,500 K

Very strong hydrogen lines290-390 nm (violet)*

F Polaris7,500 K-6,000 K

Moderate hydrogen lines, moderate lines of ionized calcium

390-480 nm (blue)*

GSun, Alpha Centauri A

6,000 K-5,000 K

Weak hydrogen lines, strong lines of ionized calcium

480-580 nm (yellow)

K Arcturus5,000 K-3,500 K

Lines of neutral and singly ionized metals, some molecules

580-830 nm (red)

MBetelgeuse, Proxima Centauri

<3,500 K

Molecular lines strong>830 nm (infrared)

*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 DiagramPlot of Brightness vs Temperature

O

Spectral Type

+10

+5

-5

Bri

ghtn

ess

0

+15B MA F G K

Sun

Sirius

Cen B

Prox Cen

Procyon

RigelCapella

Sirius B

Main Sequence

Giants

White Dwarfs

The H-R Diagram

The Main Sequence

Stars Differ By:

MassAgeComposition

Nothing else!And composition doesn’t vary

Age and Mass only.

Those on main sequence are allburning H so age drops out.

MS is function of MASS only!!!

Full, Artistic H-R

increasingsizeAT4

T constanton any verticalline

As mass ofMS star increases,both R and Tincrease

Newly Formed Star

O

Spectral Type

+10

+5

-5

M

0

+15B MA F G K

Sun

Sirius

Cen B

Prox Cen

Procyon

RigelCapella

Sirius B

Main Sequence

Giants

White Dwarfs

Protostar

Large,Low T.Settles downto MS

Then sits whileburning H

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 FuelMore Luminosity = Greater Burn Rate

We can scale from the Sun: M = 1M L = 1L

Sun lasts 1010 years

L

MMSLife 1010 M in solar masses

L in solar luminosities

Some Lifetimes

Mass Luminosity Lifetime in Billion Years

Sun 1 1 10Sirius 2 10 2Prox Cen .4 .001 4000Rigel 8 10,000 .008

Dinky little stars like Prox Cen will last trillions of yearsHuge 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