Classification of Stars – HR diagram Objectives: understand the differences between near and bright visible stars learn how to use the HR-diagram to classify stars (temperature vs. brightness) use the HR-diagram to observe the evolution of stars (when a star is born and dies) Lab Books: pages worksheet, page 115 Lab Books: pages worksheet, page 115

HR-diagram – classifies stars using temperature magnitude (brightness) HR-diagram – Hertzbrung-Russell diagram

Star color and Temperature Lets review the visible color spectrum. “What do our eyes see”? wavelength R O Y G B I V Low Energy High Energy

Star Color and Temperature R O Y G B I V 30,000 K2,5006,000 Long wave lengths Short wavelengths Cool stars Hot stars RED Yellow Blue

Measuring the Brightness of a Star “Stellar Brightness” Magnitude – the brightness of a star Apparent Magnitude a stars brightness as it appears from earth factors controlling apparent magnitude: how big the star how hot the star how far away star Which is brighter? -5 star or 5 star ? Magnitude is measured using (-) and (+) numbers the more (-) the number, the brighter the more (+), the dimmer the star

SUN Full Moon Venus Sirius North Star Naked eye PlutoHST OBJECT Apparent Magnitude Apparent Magnitude of various objects bright dim

Absolute Magnitude measures the “actual” brightness two stars with the same absolute magnitude would not be the same apparent magnitude WHY? To compare absolute brightness use a standard distance of 32.6 light-years away from earth Example: ly Apparent Magnitude Absolute magnitude Earth bright dim

Distance, Apparent Magnitude, and Absolute Magnitude of Some Stars Name Distance Light-years Apparent Magnitude Absolute Magnitude Sun NA Alpha Centauri Sirius Arcturus Betelgeuse Deneb ly View from Earth So, which star is biggest to smallest?

Brightness scale – Using Absolute Magnitude The brighter, the bigger the star BrightDim Sun Centauri Sirius Arcturs Betelgeuse Deneb

Surface Temperature (K) ,00014,00020,000 How are stars classified? – the Hertzsprung-Russell Diagram (HR-diagram) Absolute Magnitude Very Bright Very Dim O BAFGKM

Oh, Be A Fine Guy (or Gal), Kiss Me O 0 O 1 …..O 9 B 0 …..B 9 A 0 …..A 9 F…………… Hottest Coolest Spectral class: based on their spectrum (color they emit resulting from the chemical make-up) Spectral class: based on their spectrum (color they emit resulting from the chemical make-up) O B A F G K M

HR-Diagram Surface Temperature (K) ,00014,00020,000 Cool, bright Hot, dim The Brighter, The Hotter The cooler, the dimmer

O O B B A A F F G G K K M M

Surface Temperature (K) ,00014,00020,000 Dust and gasses Protostar Main Sequence Star Red Giant Stage Variable Star stage Planetary Nebula Stage White Dwarf Black Hole Stage Stellar evolution HR-Diagram