Transcript The HR Diagram

The HR Diagram
The Hertzsprung
–HR Diagram
• 90% of stars are
found on a
diagonal line
called the main
sequence
• Hotter on the left
cooler on the
right
• Brighter at top
dimmer at bottom
Russell diagram
Groups of Stars
•
•
•
•
Main sequence—diagonal line
Red Giants– bright and cool
Supergiants—brighter and cooler
White Dwarfs—dim and hot
Color and Stars
Think of a candle
• Hottest part is blue
• Red is the cool part
at the top
Spectral Class
• OBAFGKM
• Oh Be A Fine Girl Kiss Me
Annie J Cannon
(1863-1941)
• Indicates a stars composition
All Types of Stars
Recall Stars have Different colors
which indicate different temperatures
All Types of Stars
Out
Fiery
Gases
Many Red
Oh! Beyond
Be
Oh!
a Fine
BeAndromeda,
a Girl
Fine- Girl
Kiss- Me
KissRight
Me
!NowKindle
Sweetheart
!
New Stars
Star classification
• If we look at a star
with a spectroscope
we see dark lines
called absorption
spectra
• These lines indicate
the stars chemical
composition
Absolute vs. Apparent
Magnitude
Absolute —how bright a star actually is
Apparent—how bright it appears from
Earth
Revisit the HR diagram
• Where are stars most of their lives?
• Where are they when they begin to die?
• What are they after they use up their
fuel?