Transcript The Hertzsprung-Russell Diagram

The Hertzsprung-Russell Diagram
What is the HR Diagram?
• Tool that shows
relationships and
differences between
stars.
• Relative measure of
luminosity &
temperature.
• Shows stars of
different ages/stages
at the same time.
The Basics…
• Each star is represented by a dot.
• Vertical axis shows luminosity/absolute
magnitude.
– How much energy a star radiates in 1 sec.
– How bright/dim a star appears, compared to Sun
• Horizontal axis shows surface temperature (in
K.)
– NOTICE: Goes from high temps at left side to
lower temps at right side!
Let’s Practice…
http://sunshine.chpc.utah.edu/Labs/StarLife/
support/HR_init.swf
Types of Stars
• Stars that fit the
expected pattern –
cool and dim; hot and
bright – are called
main sequence
stars
– Most stars fall in the
region called main
sequence.
– Curved line sloping
from top left to lower
right of HR diagram.
Why is there a “main sequence”?
• Usually there is a predictable relationship
between brightness and temp.
Hotter things are brighter
Hotter temp = more energy is radiated.
Bigger stars are brighter.
Bigger surface area = more energy radiated.
Exception to the rule!
• Some stars are cool but if they are
massive enough, they can have high
luminosity  red giants or supergiants
Another Exception to the Rule
• Some stars are very hot and shine
intensely but are small so they don’t
radiate much energy (appear dim)  white
dwarf stars
Let’s see how a star changes
throughout its life…
http://sunshine.chpc.utah.edu/Labs/StarLife/
support/HR_animated.swf
More Practice!
http://sunshine.chpc.utah.edu/Labs/StarLife/
support/HR_static.swf