# 8.3 Exploring Other Stars Homework: page 349 # 1, 3, 8.

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8.3 Exploring Other Stars Homework: page 349 # 1, 3, 8

Key Concepts: A star’s apparent brightness depends on its luminosity and distance from Earth. A star’s apparent brightness depends on its luminosity and distance from Earth. Hertzsprung and Russell independently discovered that each type of star has specific properties. They organized their findings into what is now called a Hertzsprung and Russell ( H-R) diagram Hertzsprung and Russell independently discovered that each type of star has specific properties. They organized their findings into what is now called a Hertzsprung and Russell ( H-R) diagram

Key Concepts: The main sequence is a narrow band of stars on the H-R diagram that runs diagonally from the upper left ( bright, hot stars) to the lower right ( dim, cool stars). About 90 percent of stars are on the main sequence, including the Sun. The main sequence is a narrow band of stars on the H-R diagram that runs diagonally from the upper left ( bright, hot stars) to the lower right ( dim, cool stars). About 90 percent of stars are on the main sequence, including the Sun. A star’s position on the main sequence is determined by its initial mass. A star’s position on the main sequence is determined by its initial mass.

Key Concepts: A star will become a white dwarf, a neutron star, or a black hole, depending on its initial mass. A star will become a white dwarf, a neutron star, or a black hole, depending on its initial mass. Canadian researchers contribute to our understanding of space. Canadian researchers contribute to our understanding of space.

How bright is that star? Luminosity is a measure of the total energy output a star radiates/second Luminosity is a measure of the total energy output a star radiates/second Joules/secondJoules/second Absolute magnitude is the brightness of a star Absolute magnitude is the brightness of a star As if all stars are 32.6 light years from usAs if all stars are 32.6 light years from us Absolute magnitude of sun is 4.7Absolute magnitude of sun is 4.7

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

Star Properties: Colour Astronomers use a star’s colour to determine its surface temperature Astronomers use a star’s colour to determine its surface temperature Sun’s photosphere = 6000°C  YellowSun’s photosphere = 6000°C  Yellow Logical that other yellow stars should be similar temperature Logical that other yellow stars should be similar temperature Blue stars are very hotBlue stars are very hot 21 000 – 35 000°C 21 000 – 35 000°C Red stars, not so muchRed stars, not so much 3300°C 3300°C

Star’s Properties: Composition Different stars emit different light Different stars emit different light Light can be analyzed by a spectroscope to determine its wavelength and spectral lines Light can be analyzed by a spectroscope to determine its wavelength and spectral lines The star’s spectral lines identifies the elements within the star’s photosphere The star’s spectral lines identifies the elements within the star’s photosphere

Inquiry Practice! Try: Try: Inquiry Investigation 8-B Answer questions 1-5 (Analyze & Interpret)Answer questions 1-5 (Analyze & Interpret)

Star Properties: Mass Determining the mass of stars was impossible until astronomers discovered most stars seen from Earth are Binary stars Determining the mass of stars was impossible until astronomers discovered most stars seen from Earth are Binary stars 2 stars that orbit together (same orbit)2 stars that orbit together (same orbit) By measuring orbit size and time lapsed, it is possible to calculate “solar mass”By measuring orbit size and time lapsed, it is possible to calculate “solar mass” Sun = 1 solar massSun = 1 solar mass Exception: The Sun is not binary Exception: The Sun is not binary

Hertzsprung-Russell Diagram In the 1920’s, 2 astronomers looked for patterns in star data In the 1920’s, 2 astronomers looked for patterns in star data Independently, they observed that star types have characteristic properties that are related: Independently, they observed that star types have characteristic properties that are related: TemperatureTemperature ColourColour LuminosityLuminosity

Hertzsprung-Russell Diagram

The “Main Sequence” Central band of stars stretching across, down H-R diagram Central band of stars stretching across, down H-R diagram Accounts for 90% of the stars viewed from EarthAccounts for 90% of the stars viewed from Earth

Evolution of a Star Stars can shine for billions of years with little change Stars can shine for billions of years with little change However, the radiate massive quantities of energy  they can’t last forever! However, the radiate massive quantities of energy  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 become In the final stages of a star’s life, it will become 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 mass The fate of the star depends on its initial mass

Stellar 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

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