Chapter 19 Stars, galaxies and the Universe

Section 1 Stars

Star Color Hot stars - blue/white (10,000-30,000 C) Hot stars - blue/white (10,000-30,000 C) Warm stars - yellow/orange (3,500-10,000 C) Warm stars - yellow/orange (3,500-10,000 C) Cool stars - red (less than 3,500 C) Cool stars - red (less than 3,500 C) BetelgeuseOur SunSirius/Rigel

What are stars made of? Made of different elements in gas form Made of different elements in gas form Key elements of stars are hydrogen and helium Key elements of stars are hydrogen and helium Fusion of gases create energy in stars

Star Composition Astronomers use spectroscopes to analyze the light from a star Spectroscopes separate light into the colors of the spectrum or ROY G BIV

3 spectrum types Continuous- spectrum of true white light Bright Line- colors that elements give off as gas when heated Dark Line- colors seen when light from a star passes through the atmosphere of a star or planet.

Each element on the periodic table has its own bright line spectra “fingerprint” or “barcode” A spectrograph of a star tells us: gas composition temperature

Classifying Stars By temperature and brightness By temperature and brightness Harvard Spectral Class System Harvard Spectral Class System O: 30, ,000 K Blue stars O: 30, ,000 K Blue stars30, ,000 KBlue30, ,000 KBlue B: 10, ,000 K Blue-white stars (Rigel) B: 10, ,000 K Blue-white stars (Rigel)10, ,000 K10, ,000 K A: 7, ,000 K White stars (Vega, Sirius) A: 7, ,000 K White stars (Vega, Sirius)7, ,000 KWhite7, ,000 KWhite F: 6, ,500 K Yellow-white stars F: 6, ,500 K Yellow-white stars6, ,500 K6, ,500 K G: 5, ,000 K Yellow stars (Sun) G: 5, ,000 K Yellow stars (Sun)5, ,000 KYellow5, ,000 KYellow K: 3, ,000K Yellow-orange stars (Arcturus) K: 3, ,000K Yellow-orange stars (Arcturus)3, ,000K3, ,000K M: < 3,500 K Red stars (Betelgeuse, Antares) M: < 3,500 K Red stars (Betelgeuse, Antares)Red

Star Brightness Apparent magnitude- how bright stars appear from Earth Apparent magnitude- how bright stars appear from Earth Absolute magnitude- actual brightness of star. Absolute magnitude- actual brightness of star. Sirius- brightest star- 8.6 light years away Sirius- brightest star- 8.6 light years away Alpha Centauri- closest star- 4.3 light years away Alpha Centauri- closest star- 4.3 light years away

Absolute vs. Apparent

Determining Brightness How far is star from Earth? How far is star from Earth? Size of star (big stars give off more light) Size of star (big stars give off more light) Temperature of star (hot stars burn brighter than cool stars) Temperature of star (hot stars burn brighter than cool stars) Brightest stars not always the closest Brightest stars not always the closest North star is not even in top 20 North star is not even in top 20

Distance to stars Measured in light years (distance light travels in one year) 10 trillion miles. Measured in light years (distance light travels in one year) 10 trillion miles. Parallax used to determine distance of nearby stars. (100 light years or closer) Parallax used to determine distance of nearby stars. (100 light years or closer) Trigonometry Trigonometry

Parallax

Doppler Effect- change in spectrum wavelength caused by movement of a star We use this to determine If stars are moving toward or away from us.

A Red shift =away from us. A Blue shift = toward us. Most objects outside our galaxy have a red shift. This is evidence for the Big Bang Theory.

Star Motion Stars move in the sky because…. Stars move in the sky because…. 1. Earth orbits the sun 2. Earth is tilted 23 ½ degrees 3. Earth rotates 4. Our solar system is moving (very slow) 5. Stars are moving (very slow)

Section 2 Life Cycle of Stars