191
Characteristics of Stars
2/25/15
2/22-25/2013
Starter:
Compare the life
cycle of a star with
that of a human.
Practice: Notes
192
Characteristics of Stars
2/25/15
2/22-25/2013
Application/Connection:
HR Diagram Activity
Exit:
If there are more low-mass
stars than high-mass stars
in the universe, do you think
there are more white
dwarfs or more black holes?
Explain!
February 25, 2015
AGENDA
Objective 8.8C
Describe components
of the universe,
including stars, nebulae,
and galaxies, and use
models such as the
Herztsprung-Russell
diagram for
classification by taking
notes and a HR diagram
graph.
1. Starter
2. Notes
3 Activity
4. Exit
Table of Contents
Date
2/20
2/23
2/24
2/25
Lecture/ Activity/ Lab
Formation of the Universe
Big Bang Lab
Lives of Stars
Characteristics of Stars
Page
185-186
187-188
189-190
191-192
Characteristics of Stars
• To an astronomer stars appear very
different in many ways such as their
size, temperature, color, brightness,
density and mass.
SizeNeutron
Star
NEUTRON STAR- A very small and dense star made almost
completely of neutrons.
Neutron stars have a radius of about 10 kilometers (6.2 mi) and
a mass from about 1.4 to 5 times the mass of the Sun. The
density is a billion times the density of Earth.
They are usually what is left of supernovas.
SizeWhite
Dwarf
Our Sun, A Red Giant, and a White Dwarf
White Dwarfs are about the same size as the Earth and
200,000 times as dense. (They may weigh the same as the
sun.)
White dwarf stars are extremely hot (100,000 Kelvin); so
they emit bright white light. Because white dwarfs are
extremely small, it takes them a long time to cool down.
A star like our Sun will become a white dwarf when it has
run out of fuel. Near the end of its life, it will go through a red
giant stage, and then lose most of its gas.
Size- Medium (main sequence)
Main Sequence or Medium
size star are about the size of
our Sun which has a diameter of
about 1,392,000 km, about 109
times that of Earth, and its
density is 330,000 times that of
Earth.
Main sequence stars all
undergoing fusion of hydrogen
into helium within their cores.
Mass is the key factor in
determining the lifespan of a
main sequence star, its size and
its luminosity. Stars on the main
sequence also appear to be
unchanging for long periods of
time.
SizeGiant star
Giant star-a star with a diameter about 10 to 100 times the size
of our sun and has a lower density due to the massive size.
Giant stars are swollen in size towards the end of its life, having
converted all the hydrogen in its core to helium.
A giant star is brighter, larger, and cooler than a mainsequence star of the same mass. and luminosities from tens to
thousands of times the Sun's.
Common types of giants are: blue giant and red giant.
Size-Super
Giants
Super giant star- 1000 times the diameter of out sun;
dies out quickly and the shortest lived in the universe
(only a few million years).
Density is very slight due to super-massive size but the
luminosity is nearly 1,000,000 times as great.
The super-giant can explode (at the end of its life cycle)
into a supernova. This explosion is so powerful that for a
few weeks, this supernova can outshine an entire galaxy.
Temperature
The color of the star determines what the surface
temperature is. The hotter the star the brighter the star will
be. Temperature is measured in degrees Kelvin.
Star Type
Color
Approximate
Surface
Temperature
O
Blue
over 25,000 K
10 Lacertra
B
Blue
11,000 - 25,000 K
Rigel
Spica
A
Blue
7,500 - 11,000 K
Sirius, Vega
F
Blue to White
6,000 - 7,500 K
Canopus, Procyon
G
White to Yellow
5,000 - 6,000 K
Sun, Capella
K
Orange to Red
3,500 - 5,000 K
Arcturus,
Aldebaran
M
Red
under 3,500 K
Betelgeuse,
Antares
Examples
Mass
Elements found in most abundance
inside the Stars
Star name
H
He
Ca
Li
Na
Mg
Fe
☼
☼
☼
☼
☼
☼
☼
☼
Sun
☼
☼
Procyon
☼
☼
☼
☼
☼
Betelgeuse
☼
☼
☼
☼
☼
Sirius
☼
☼
Aldebaran
☼
☼
☼
☼
Mass- is the composition
(hydrogen, helium)of the star
As Hydrogen burns the mass
of the star increases due to
new elements being fused
together.
Ne
☼
Color
Color- ranging from blue to red
and depending on the elements
that are burning.
Most stars are currently
classified using the letters:
 O stars are called "blue"
 B "blue-white"
 A stars "white"
 F stars "yellow-white"
 G stars "yellow"
 K stars "orange"
 M stars "red"
.
Brightness (Luminosity)
Brightness is constant amount of light that is emitted by the
star.
Brightness depends on the size of the star, its surface
temperature, and its distance from the Earth.
Apparent magnitude-the brightness of a star as it appears
Absolute magnitude-the amount of light a star actually gives
off
Hertsprung-Russell Diagram
Astronomers have
discovered that
there is a
relationship
between a star’s
surface
temperature and its
brightness.
Two astronomers
named Hertsprung
and Russell
plotted the data of
the stars on a chart
according to their
surface
temperature and
brightness.
Grouping Stars on the
H-R Diagram
Hertsprung and Russell
found the stars fall into one
of three groups.
Most stars fall into a
narrow band on the chart
called the Main Sequence.
A second group appears at
the third upper right of the
chart called the giants and
supergiants.
A third group of stars
appears at the very bottom
of the chart and are called
white dwarfs.
H-R Diagram Main-sequence Stars
Main Sequence stars fall into the an area from the upper
left corner to the lower right corner of the H-R diagram
The hottest are blue or blue-white and are in the upper left
corner of the diagram
The cool, dim stars are red in the lower right corner.
191
Characteristics of Stars
2/25/15
2/22-25/2013
Starter:
Compare the life
cycle of a star with
that of a human.
Practice: Notes
192
Characteristics of Stars
2/25/15
2/22-25/2013
Application/Connection:
HR Diagram Activity
Exit:
If there are more low-mass
stars than high-mass stars
in the universe, do you think
there are more white
dwarfs or more black holes?
Explain!