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. 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. 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. 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 Joules/second Absolute magnitude is the brightness of a star Absolute magnitude of the sun is 4.7

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 Sun’s photosphere = 6000°C  Yellow Blue stars are very hot 21 000 – 35 000°C Red stars, not so much 3300°C

Star’s Properties: Composition Different stars emit different light 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

Inquiry Practice! Try: Inquiry Investigation 8-B page 352 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 2 stars that orbit together (same orbit) By measuring orbit size and time lapsed, it is possible to calculate “solar mass” Sun = 1 solar mass Exception: The Sun is not binary

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

Hertzsprung-Russell Diagram

Hertzsprung-Russell Diagram

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

Evolution of a Star Stars can shine for billions of years with little change However, the radiate massive quantities of energy  they can’t last forever! Eventually they will run out of fuel In the final stages of a star’s life, it will become A white dwarf, or A neutron star, or A black hole The fate of the star depends on its initial mass

Stellar comparison Make a table in your notes comparing: Low-mass stars Intermediate-mass stars High-mass stars (massive) Neutron stars Supernovas