Download Properties of Stars and H

Properties of
Stars
and H-R Diagrams
How WE can tell the
differences between
stars.
Objectives
• When given the color of a star, determine
the temperature.
• To tell the difference between absolute
magnitude and apparent magnitude
• Read an HR diagram to determine
•
•
•
•
•
Stage of star
Luminosity or brightness of star
Temperature & color of star
Relative size of star
Where our sun is
Surface Temperature of Stars
• Surface temperature is a measure of how much energy
is being given off on the outside of a star.
• Most of the nuclear fusion reactions happen in the core.
While nuclear fusion is happening, the core is the
hottest place in a star.
• Dense things are hotter. Large and airy things are
cooler.
• Astronomers can look at the color of light coming from a
star and determine its’ surface temperature.
Blue
very hot
20,000
White
hot
Red
cool
Yellow
warm
7,000
5,000
Temperature in Kelvin
2500
How Bright is that STAR?
Luminosity is how we measure the brightness
of a star.
Dim Light
Bright Light:
There are 2 ways to measure brightness:
• Apparent magnitude – when we use size,
temperature, and distance to earth to calculate
brightness. This is not a true measure because
stars closer to Earth will appear brighter to us.
•
Absolute magnitude – a star’s actual or real
level of brightness in comparison with other
stars.
Which Star is Brighter?
• From Earth, both
stars A and B seem
like they have the
same brightness.
• Because we see this
from earth, we say
that the apparent
magnitude is the
same.
• In reality, Star B is
far brighter, but it is
just farther away.
• We would say that
the actual magnitude
of star B is far brighter
than star A.
Hertzsprung Russell (HR)
Diagrams
• We can use HR diagrams to study several
characteristics about stars
• Luminosity (compared to the sun)
• Brightness (Absolute Magnitude as compared
to the sun)
• The sun is at 1 absolute magnitude
• Surface Temperature
• Stage of life cycle
• Be careful!! HR diagrams look the same,
but look at the x axis and y axis to know
what the diagram is measuring!!
Our sun
1
HR Diagrams show
ts t.
e
g ho
r
how stars change over Once they start burning
ta eHelium,
ry
s
v
e ebeocmes
The star swells
time. As th
hand
t
s
,
like marshmallows
s en
bri ey g
p
d
o
t
gh e t
e
ter old n s or
en be sieor s m
erg cfau e, tth
y ar usge ey
le byhenn the get
c
u l, t uc y m ho
n
tte
lea
r al
a
e
t m
r fu ke r a
f
s
A y
sio mor nd
r
Temperature
is backwards!!
e It goes
n!
ve
from high temperature to low
temperature!
Key Points of H-R
Diagrams
•
•
•
•
•
•
Hottest Stars are the brightest stars.
Coolest stars are the dimmest
Blue stars are more dense and hotter
Red stars are more airy and colder.
Cooler stars live longer than hot stars. Why?
Because they “cook more slowly” in a cold oven!
Hot stars “cook” at a higher temperature.
Diagonal
Lines
represent the
radius of the
star.
The hottest
stars are the
brightest are
blue.
The coolest
stars are the
dimmest, or the
most pale.
Review
What does apparent and actual magnitude
measure?
Luminosity or how bright the star is
How can you tell temperature by color?
From cold to hot:
Red Yellow White Blue
On the HR diagram, what stage are most
stars in?
Main Sequence
Big Picture Review
What elements are made in the following
stages:
Main sequence
Helium
Carbon
Red Giant
Carbon to Iron (Fe)
Supergiant
Supernova All elements heavier than Iron (Fe)
Star X is in the Red Giant stage. How big
is its’ mass?
Like the Sun.