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What is a Hertzsprung-Russell
Diagram?
Luminosity
An H-R
diagram plots
the
luminosity
(light-energy
emitted/time)
and
temperature
of stars
Note: stars
do not
uniformly
fill the
diagram!
Temperature
Normal hydrogenburning stars reside
on the main
sequence of the
H-R diagram
Stars spend the
majority of their
life on the main
sequence.
High-Mass Stars
Low-Mass Stars
Normal hydrogenburning stars reside
on the main
sequence of the
H-R diagram
Large radius
Small radius
Stars with low
temperature and
high luminosity
must have large
radius
SUPERGIANTS
GIANTS
Stars with low
temperature and
high luminosity
must have large
radius
SUPERGIANTS
GIANTS
WHITE
DWARFS
Stars with low
temperature and
high luminosity
must have large
radius
H-R diagram
depicts:
Temperature
Luminosity
Color
Spectral Type
Luminosity
Radius
Mass
Lifespan
Age
Temperature
C
Luminosity
B
Which star is
the hottest?
D
A
Temperature
C
B
Which star is
the hottest?
Luminosity
A
D
A
Temperature
C
Luminosity
B
Which star is the
most luminous?
D
A
Temperature
C
Luminosity
B
Which star is the
most luminous?
C
D
A
Temperature
C
Luminosity
B
Which star is
burning
hydrogen in its
core?
D
A
Temperature
C
Luminosity
B
Which star is
burning
hydrogen in its
core? (It’s a main
sequence star)
D
A
Temperature
D
C
Luminosity
B
Which star has
the largest
radius?
D
A
Temperature
C
B
Which star has
the largest
radius?
Luminosity
C
D
A
Temperature
A
Which star is
most like our
Sun?
Luminosity
D
B
C
Temperature
A
Which star is
most like our
Sun?
Luminosity
D
B
C
Temperature
B
A
Luminosity
D
B
C
Temperature
Which of these
stars will have
changed the least
10 billion years
from now?
A
Luminosity
D
B
C
C
Temperature
Which of these
stars will have
changed the least
10 billion years
from now?
A
Luminosity
D
B
C
Temperature
Which of these
stars can be no
more than 10
million years old?
A
Luminosity
D
A
B
C
Temperature
Which of these
stars can be no
more than 10
million years old?
How can we know this if stars
live millions or billions of
years?
Stars in a Star Cluster
1) Born at the same
time
2) All about the same
distance
3) Same chemical
composition
1) Because they formed
from the same gas
cloud
How do we measure the age
of a star cluster?
Pleiades now has
no stars with life
expectancy less
than around 100
million years
Main-sequence
turnoff
Main-sequence
turnoff point of a
cluster tells us its
age
Detailed
modeling of the
oldest globular
clusters reveals
that they are
about 13 billion
years old