Download 15.2 Characteristics of Stars

Chapter 15, Section 2:
Characteristics
of Stars
Page 598
Classifying Stars
• Scientists classify stars according
to
–Color
–Temperature
–Size
–Chemical composition
–Brightness
Color, Temperature and Size
• Stars vary greatly in color. Different
colors reveal the star’s temperature.
Betelgeuse looks reddish; Rigel looks
blue-white; our sun appears yellowish.
Color, Temperature and Size
• Stars vary greatly in size. Giant stars are
typically 10 to 100 times larger than the
sun and more than 1,000 times the size of
a white dwarf.
Electromagnetic Spectrum
• Electromagnetic radiation is energy
that can travel through space in the
form of waves.
Increasing Energy
You actually know more about it than you may think! The
electromagnetic spectrum is just a name that scientists give a
bunch of types of radiation when they want to talk about them as a
group. Radiation is energy that travels and spreads out as it
goes– visible light that comes from a lamp in your house and radio
waves that come from a radio station are two types of
electromagnetic radiation.
Types of EM radiation are:
1. Radio Waves
5. Ultra violet
2. Microwave
6. X-rays
3. Infrared
7. Gamma rays
4. Visible Light
• Radio waves: This is the
same kind of energy that
radio stations emit into
the air for you to capture
and turn into your favorite
Mozart, Madonna, or The
Fray tunes.
• But radio waves are also
emitted by other things ...
such as stars and gases
in space.
Microwaves: They will
cook your popcorn in
just a few minutes!
Microwaves in space
are used by
astronomers to learn
about the structure of
nearby galaxies, and
our own Milky Way!
• Infrared Rays: Our
skin emits infrared
light (heat), which is
why we can be seen
in the dark by
someone using night
vision goggles.
• In space, IR light
maps the dust
between stars.
• Visible light: This is
the part that our eyes
see. Visible radiation
is emitted by
everything from
fireflies to light bulbs
to stars ... also by
fast-moving particles
hitting other particles.
• Ultraviolet: We know
that the Sun is a
source of ultraviolet
(or UV) radiation,
because it is the UV
rays that cause our
skin to burn!
• Stars and other "hot"
objects in space emit
UV radiation
• X-Rays: Your doctor
uses them to look at
your bones and your
dentist to look at your
teeth.
• Hot gases in the
Universe also emit Xrays.
• Gamma Rays:
Radioactive materials
(some natural and others
made by man in things
like nuclear power plants)
can emit gamma-rays..
• But the biggest gammaray generator of all is the
Universe! It makes
gamma radiation in all
kinds of ways.
Visible Light
Regular visible light is really a combination
of several colors.
Red
Orange
Yellow
Green
Blue
Indigo Violet
Different gases, when ionized, will give off different
color bands of light.
Star Spectrums
Astronomers can use line spectrums to identify
the chemical elements in a star. Each element
produces a characteristic pattern of spectral lines.
Measuring with Light
• When stars are moving toward Earth, their
wavelengths appear to be shortened or shirt
toward the blue side of the spectrum
• When stars are moving away from Earth, their
wavelengths appear to be lengthened or shirt
toward the red side of the spectrum
• Site
Brightness
• The brightness of stars depend upon
both its size and its temperature.
Its apparent brightness depends on its
distance from Earth. The sun, which is
only average in brightness, appears to be
the brightest, because it is closest.
Absolute Brightness
• Absolute brightness refers to the
brightness of the star as if it were a
standard distance from Earth.
• If we were to place all stars 93 million
miles from Earth (the distance away of
our sun) we would see that the sun is
of only average brightness.
Measuring Distances
• Because distances in the universe are so
large, astronomers use units other than
meters to measure distances.
• Two units of measure that astronomers
use are astronomical units and light-years.
• One astronomical unit (1 AU) is equal to
the average distance the Sun is from the
Earth or 93 million miles or 150 million
kilometers.
Measuring Distances
• A light-year is the distance a particle of
light would travel in one year’s time. It is a
measure of distance.
Light travels at 186,000 miles per second or
3 X 108 meters per second.
In one year, light would travel
5,860,000,000,000 miles or
9,500,000,000,000,000 meters.
Measuring Distance: Parallax
• Parallax is the apparent change in position of an
object when you look at it from different places.
Measuring Distances to Stars
• Astronomers often use parallax to
measure distances to nearby stars.
The Hertzsprung-Russell
Diagram
Astronomers
use H-R
diagrams to
classify stars
and to
understand
how stars
change over
time.
End of Section:
Characteristics
of Stars
Read 15.2, Do the section questions 1a – 3c
on page 605