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

2. 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

3. 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.

4. 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.

5. 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

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

7. 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
– °C
Red stars, not so much
3300°C

8. 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

9. Inquiry Practice! Try: Inquiry Investigation 8-B page 352
Answer questions 1-5 (Analyze & Interpret)

10. 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

11. 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

12. Hertzsprung-Russell Diagram

13. Hertzsprung-Russell Diagram

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

15. 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

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