Types of StarsTypes of Stars

3.33.3

How bright is that star?How bright is that star?

Luminosity is a measure of the total Luminosity is a measure of the total energy output a star radiates/secondenergy output a star radiates/second• Joules/secondJoules/second

Absolute magnitude is the brightness Absolute magnitude is the brightness of a starof a star• As if all stars are 32.6 light years from As if all stars are 32.6 light years from

usus• Absolute magnitude of sun is 4.7Absolute magnitude of sun is 4.7

A star’s apparent A star’s apparent magnitude (how magnitude (how bright it appears on bright it appears on Earth) depends on Earth) depends on its brightness and its brightness and distance from Earthdistance from Earth

Star Properties: ColourStar Properties: Colour

Astronomers use a star’s colour to Astronomers use a star’s colour to determine its surface temperaturedetermine its surface temperature• Sun’s photosphere = 6000°C Sun’s photosphere = 6000°C Yellow Yellow

Logical that other yellow stars should be Logical that other yellow stars should be similar temperaturesimilar temperature

• Blue stars are very hotBlue stars are very hot 21 000 – 35 000°C21 000 – 35 000°C

• Red stars, not so muchRed stars, not so much 3300°C3300°C

Star’s Properties: CompositionStar’s Properties: Composition Different stars emit different lightDifferent stars emit different light Light can be analyzed by a spectroscope to Light can be analyzed by a spectroscope to

determine its wavelength and spectral linesdetermine its wavelength and spectral lines The star’s spectral lines identifies the elements The star’s spectral lines identifies the elements

within the star’s photospherewithin the star’s photosphere

http://www.youtube.com/watch?v=l4yg4HTm3ukhttp://www.youtube.com/watch?v=l4yg4HTm3uk

Inquiry Practice!Inquiry Practice!

Try: Try:

Inquiry Investigation 8-BInquiry Investigation 8-B

• Answer questions 1-5 Answer questions 1-5 (Analyze & Interpret)(Analyze & Interpret)

Star Properties: MassStar Properties: Mass

Determining the mass of stars was Determining the mass of stars was impossible until astronomers impossible until astronomers discovered most stars seen from Earth discovered most stars seen from Earth are are Binary starsBinary stars• 2 stars that orbit together (same orbit)2 stars that orbit together (same orbit)• By measuring orbit size and time lapsed, it By measuring orbit size and time lapsed, it

is possible to calculate “solar mass”is possible to calculate “solar mass”• Sun = 1 solar massSun = 1 solar mass

Exception: The Sun is not binaryException: The Sun is not binary

Hertzsprung-Russell DiagramHertzsprung-Russell Diagram

Read p. 343-344Read p. 343-344 Complete handoutComplete handout

Hertzsprung-Russell DiagramHertzsprung-Russell Diagram

In the 1920’s, 2 astronomers looked In the 1920’s, 2 astronomers looked for patterns in star datafor patterns in star data

Independently, they observed that Independently, they observed that star types have characteristic star types have characteristic properties that are related:properties that are related:• TemperatureTemperature• ColourColour• LuminosityLuminosity

Hertzsprung-Russell DiagramHertzsprung-Russell Diagram

Hertzsprung-Russell DiagramHertzsprung-Russell Diagram

The “Main Sequence”The “Main Sequence”

Central band of stars stretching Central band of stars stretching across, down H-R diagramacross, down H-R diagram• Accounts for 90% of the stars viewed Accounts for 90% of the stars viewed

from Earth from Earth

Evolution of a StarEvolution of a Star Stars can shine for billions of years with little Stars can shine for billions of years with little

changechange However, the radiate massive quantities of However, the radiate massive quantities of

energy energy they can’t last forever! they can’t last forever!• Eventually they will run out of fuelEventually they will run out of fuel

In the final stages of a star’s life, it will In the final stages of a star’s life, it will becomebecome• A white dwarf, orA white dwarf, or• A neutron star, orA neutron star, or• A black holeA black hole

The fate of the star depends on its initial The fate of the star depends on its initial massmass

Stellar comparisonStellar comparison

Make a table in your notes comparing:Make a table in your notes comparing:• Low-mass starsLow-mass stars• Intermediate-mass starsIntermediate-mass stars• High-mass stars (massive)High-mass stars (massive)• Neutron starsNeutron stars• SupernovasSupernovas

Make it detailed and neat. This will be on Make it detailed and neat. This will be on a quiz/test/exam!a quiz/test/exam!