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Notes - Stars
Chapter 12, Lesson 1
Stars
• Stars are balls of gas, mostly hydrogen, that
produce light by nuclear reactions in their
cores.
Star Structure
• Stars have layered structures.
• Energy is produced in the core.
• Temperatures range from 5,000,000 K to
100,000,000 K in the core.
• Atoms separate from their nuclei, forming
plasma.
Star Structure
Star Types
• Stars have many
diameters, masses, and
surface temperatures.
• Our Sun is a mediumsized star with a surface
temperature of about
5800 K.
Star Types
Properties of Different Types of Stars
Type
Supergiant
Diameter
(1=Sun’s dia.)
100 – 1,000
Mass
(1=Sun’s mass)
8-17
Surface
Temp. (K)
Variable
Red Giant
10-100
1-4
3,000 – 4,000
Main
Sequence
White Dwarf
0.1 – 15
0.1 – 60
2,400 – 50,000
0.01
0.5 – 1.44
6,000 – 100,000
Neutron Star
0.00
1-4
variable
Star Distances
• One AU is the average distance between the
Sun and Earth.
• A light-year is the distance light travels in
one year: 9,500,000,000,000 km or 63,000
AU.
Star Distances
Star Composition
• Stars can only be studied
by the light they emit.
• A spectroscope is an
instrument that is used to
study light.
• Astronomers can
determine what elements
are present in a star.
Star Composition
• Light split by a prism into a rainbow is a
continuous spectrum.
• A continuous spectrum is emitted by hot,
dense materials, such as the gas of the Sun’s
photosphere.
Star Composition
• Dark lines are sometimes seen in a
spectrum, called an absorption spectra.
• Absorption spectra are produced when light
passes through cooler gases that absorb
certain wavelengths.
Star Composition
• Each element absorbs only certain
wavelengths.
Star Composition
• Absorption lines help astronomers identify
elements in stars.
Star Temperature
• As metal gets hotter, it changes from red to
yellow to white.
• The color of stars also depends on
temperature.
Star Temperature
• Every object emits electromagnetic
radiation.
• The wavelength emitted depends on the
temperature of the object.
- Objects at room temperature emit long, infrared
waves.
- As temperature rises, wavelengths become
shorter.
Star Temperature
Star Temperature
Oh Boy, Another F's Gonna Kill Me.
The
temperature of
a star is
indicated by
the color it
glows.
(The Harvard
Stellar
Classification
System)
Type of Star
Color
Surface Temp (oC)
O
Blue
Above 25,000
B
Blue-White
10,000 – 25,000
A
White
7,500 – 10,000
F
Yellow-White
6,000 – 7,500
G
Yellow
5,000 – 6,000
K
Orange
3,500 – 5,000
M
Red
Below 3,500
Star Brightness
• The brightness of stars depends on
two things: energy and distance.
• Light looks brighter as you move
closer to the source.
• Luminosity is measured by how
much energy in joules is released
per second.
• One joule per second is called a
watt.
Star Brightness
• Apparent magnitude is the apparent
brightness of a star as measured on Earth.
- Apparent magnitude depends on the star’s
actual brightness and distance.
- The smaller the magnitude number, the brighter
the star. (http://spaceweather.com/flybys )
Star Brightness
• Absolute magnitude is the apparent
magnitude it would have if it were 32.6
light years away from Earth.
Star Brightness
Star Classifications
• Two astronomers independently developed
diagrams of how absolute magnitude, or
luminosity is related to the temperature of
stars.
• The diagram that plots temperature vs.
absolute magnitude is called the
Hertzsprung-Russell Diagram.
Star Classifications
• 90% of stars fall on a diagonal, curved line,
called the main sequence.
• The remaining stars fall into one of three
other groups.
- Red giants
- Supergiants
- White dwarfs
Star Classifications
Star Classifications
The apparent brightness of a star
depends on what two things?
A magnitude and distance
B distance and temperature
C distance and absolute brightness
D absolute brightness and temperature
12.1 Stars
A light-year is a unit of ____.
A time
B temperature
C brightness
D distance
As a star increases in absolute
magnitude, it appears ____ on Earth.
A larger
B hotter
C brighter
D more dense
The average distance between Earth
and the Sun is called a(n) ____.
A light-year
B astronomical unit
C angstrom
D solar unit
SCI 4.d
A star that is blue in color is ____
than a star red in color.
A hotter
B cooler
C larger
D smaller