3. Section 1: Stars
By the end of this section, you should be able to:
Describe how color indicates the temperature of a
star
Explain how a scientist can identify a star’s
composition
Describe how scientists classify stars.
Compare absolute magnitude with apparent
magnitude.
Identify how astronomers measure distances from
Earth to stars.
Describe the difference between the apparent
motion and the actual motion of stars.
4. Composition of Stars
Because a blue flame is hotter than a yellow or
red flame, we can conclude that blue stars are
hotter than yellow or red stars.
5. Composition of Stars
A star is made of different elements in the form
of gases.
The gases in the atmosphere of a star absorb
different wavelengths of light radiating from the
star, depending on which elements make up
the gases.
6. Composition of Stars
The light from a star indicates which elements
make up that star.
A prism breaks white light into a rainbow of
colors called a spectrum.
An instrument called a spectrograph is used to
break a star’s light into a spectrum. The
spectrum of a star will vary depending on
which elements are present.
7. Composition of Stars
Emission lines are lines made when certain
wavelengths of light, or colors, are given off by
hot gasses.
Each element produces a unique set of
emission lines, which allows them to be used
to identify the elements in a star.
9. Fingerprinting Cars
Police use spectrographs to “fingerprint” cars.
Car makers put trace elements in the paint of
cars. Each make of car has a special paint and
thus its own combination of trace elements.
When a car is in a hit-and-run accident, police
can ID the make of the car by the paint left
behind.
10. Composition of Stars
A star’s spectrum is made of dark emission
lines. A star’s atmosphere absorbs certain
colors of light, which causes black lines to
appear.
Because a star’s atmosphere absorbs some
colors of light, the spectrum of a star is called
an absorption spectrum. It can be used to
identify some of the elements in a star’s
atmosphere.
12. Classifying Stars
Stars are now classified by how hot they are.
The brightest star, Sirius, has a magnitude
of -1.4. The dimmest star that can be seen with
a microscope has a magnitude of 29.
14. Classifying Stars
The brightness of a light or star is called
apparent magnitude.
Absolute magnitude is the actual brightness of
a star.
15. Distance to the Stars
Because stars are so far away, astronomers
use light-years to measure the distances from
Earth to the stars.
A light year is the distance that light travels in a
year.
17. Distance to the Stars
Parallax is the apparent shift in the position of
an object when viewed from different locations.
Measuring parallax enables scientists to
calculate the distance between a star and the
Earth.
18.
19. Motions of Stars
If you look at the night sky long enough, the
stars also appear to move.
The apparent motion of the sun and stars in
our sky is due to Earth’s rotation. But each star
is also moving in space. Their actual
movements, however, are difficult to see.
24. Section 2: Life Cycle of Stars
By the end of this section, you should be able to:
Describe different types of stars.
Describe the quantities that are plotted in the
H-R diagram.
Explain how stars at different stages in their
life cycle appear on the H-R diagram.
25. Beginning and End of Stars
A star enters the first stage of its life cycle as a
ball of gas and dust.
Gravity pulls the gas and dust together, and
hydrogen changes to helium in a process
called nuclear fusion.
26. Beginning and End of Stars
Stars usually lose material slowly, but
sometimes they can lose material in a big
explosion. Much of a star’s material returns to
space, where it sometimes forms new stars.
27. Different Types of Stars
Stars can be classified by their size, mass,
brightness, color, temperature, spectrum, and
age. A star’s classification can change as it
ages.
28. Different Types of Stars
After a star forms, it enters the second and
longest stage of its life cycle known as the
main sequence.
During this stage, energy is generated in the
core as hydrogen atoms fuse into helium
atoms.
29. Different Types of Stars
After the main-sequence stage, a star can
enter the third stage of its life cycle when it can
become a red giant.
As the center of the star shrinks, the
atmosphere of the star grows very large and
cools to form a red giant or a red supergiant.
30. How Giant?
Red giants can be 10 or more times bigger
than the sun.
Supergiants are at least 100 times bigger than
the sun.
31. Different Types of Stars
In the final stages of its life cycle, a star with
the same mass as the sun or smaller can
become a white dwarf.
A white dwarf can no longer generate energy
through nuclear fusion. They can shine for
billions of years before they cool completely.
32. A Tool for Studying Stars
The Hertzprung-Russell diagram is a graph
that shows the relationship between a star’s
surface temperature and absolute magnitude.
The diagonal pattern on the H-R diagram
where most stars lie is called the main
sequence.
34. When Stars Get Old
A supernova is a gigantic explosion in which a
massive blue star collapses.
A star that has collapsed under gravity to the
point at which all of its particles are neutrons is
called a neutron star.
35. When Stars Get Old
If a neutron star is spinning, it is called a
pulsar.
Sometimes the leftovers of a supernova are so
massive that they collapse to form a black
hole.
A black hole is an object that is so massive
that even light cannot escape its gravity.
38. Warmup
Describe the evidence that indicates that the
galaxy is rotating.
What other objects have you seen look similar
to a spiral galaxy? Do they rotate?
39. Section 3: Galaxies
By the end of this section, you should be able to:
Identify three types of galaxies.
Describe the contents and characteristics of
galaxies.
Explain why looking at distant galaxies reveals
what young galaxies looked like.
40. Types of Galaxies
A galaxy is a collection of stars, dust, and gas
held together by gravity.
41. Types of Galaxies
Spiral galaxies have a bulge at the center and
spiral arms.
Astronomers think that our solar system is in a
spiral galaxy.
42. Types of Galaxies
About one-third of all galaxies are simply
massive blobs of stars. These are called
elliptical galaxies.
44. What are Galaxies Made Up Of?
A large cloud of gas and dust in interstellar
space is called a nebula.
45. What are Galaxies Made Up Of?
A globular cluster is a tight group of stars that
looks like a ball and contains up to 1 million
stars.
46. What are Galaxies Made Up Of?
An open cluster is a group of stars that are
close together relative to surrounding stars.
47. Origins of Galaxies
Because it takes light time to travel through
space, looking at distant galaxies reveals what
early galaxies looked like.
48. Origins of Galaxies
A very luminous, star-like object that generates
energy at a high rate is called a quasar. Some
scientists think that quasars may be the core of
young galaxies that are in the process of
forming.
50. Warmup
The first image represents the initial explosion
of the big bang, and the following images
represent the expansion of the universe and
the formation of the galaxies.
Describe the differences between the images.
51. Section 4: Formation of the Universe
By the end of this section, you should be able to:
Describe the big bang theory.
Explain evidence used to support the big bang
theory.
Describe the structure of the universe.
Describe two ways scientists calculate the age
of the universe.
Explain what will happen if the universe
expands forever.
52. Universal Expansion
Cosmology is the study of the
origin, properties, processes, and evolution of
the universe.
To understand how the universe
formed, scientists study the movement of
galaxies.
53. Universal Expansion
The universe, like the rising raisin bread
dough, is expanding. Think of the raisins in the
dough as galaxies. As the universe
expands, the galaxies move farther apart.
54.
55. The Big Bang Theory
The theory that the universe began with a
tremendous explosion is called the big bang
theory.
56. The Big Bang Theory
In 1964, two scientists using a huge antenna
accidentally found radiation coming from all
directions in space. One explanation for this
radiation is that it is cosmic background
radiation left over from the big bang.
58. How Old is the Universe?
Scientist use two methods to estimate the age of
the universe.
By measuring the distance between Earth and
various galaxies, scientists can predict the rate of
expansion and calculate the age of the universe.
Because the universe must at least be as old as
the oldest stars it contains, the ages of the stars
provide a clue to the age of the universe.
59. A Forever Expanding Universe
The expansion of the universe depends on the
amount of matter it contains.
A large enough quantity of matter would cause
gravity to stop the expansion. The universe
could start collapsing.
60. A Forever Expanding Universe
Scientists now think that there may not be
enough matter in the universe, so the universe
would continue to expand forever and become
cold and dark as all the stars die.
