Page
Name: ……….. Date: ………
Student Exploration: Big Bang Theory – Hubble’s Law
Vocabulary: absolute brightness, absorption spectrum, apparent brightness, Big
Bang theory, blueshift, Cepheid variable, Doppler shift, Hubble constant, Hubble’s
law, luminosity, megaparsec, period, redshift, spectrograph
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
Standing by the side of a lonely highway at night, you see two motorcycle
headlights, one in each direction. The headlight on your left appears brighter than
the one on your right.
1. If the headlights are equally bright, which motorcycle is closer?
Explain: The motorcycle to your left is closer because the other motorcycle on
the other side of the highway which is farther. This means that whatever side
of the highway you're on, the motorcycle to your left will be closer although
they’re equally bright because the motorcycle on the other side will still be
farther.
2. Suppose the dim-looking headlight on the right is actually a small light on
the front of a bicycle. What can you conclude about the distance of the
motorcycle and bicycle?
They can be farther or closer, but it is hard to tell because the lights are different
from each other.
Gizmo Warm-up
In 1912, an astronomer named Henrietta Swan
Leavitt studied a class of stars called Cepheid
variables. These stars change from bright to dim
to bright again. Her discoveries led to a method
of measuring distances to other galaxies and
eventually helped to support the Big Bang theory
Page 1 of 21
, Page
of the origin of the universe.
Page 2 of 21
, Page
In the Big Bang Theory – Hubble’s Law Gizmo, select Region A. Look at the image of
the Andromeda Galaxy, a galaxy relatively close to our own Milky Way galaxy.
1. Locate the two Cepheid variables, the stars that change in brightness over
time. Star A-091 is the yellow star, and A-171 is the white star.
A. Which star reaches a greater apparent brightness?
I would say the yellow star because it looks brighter. But, it might just be
because yellow is brighter than white.
B. Which star takes longer to
pulse? The yellow star takes
longer to pulse.
2. Because both stars are in the same galaxy, they are about the same distance
from Earth. Based on what you see, how is the brightness of the star related to
how quickly it pulses?
The yellow star is brighter than the white star but it might be because the yellow
star gradually gets brighter. With the white star it brightens really quick.
Get the Gizmo ready:
Activity A:
● On the STARS tab, check that Region A:
Period and
NGC 224 (Andromeda Galaxy) is selected. If
brightness
not, click Return to map and select Region
A.
Introduction: Two factors determine how bright a star appears to an observer: its
luminosity, or absolute brightness, and its distance from the observer. A star may
appear bright because it is a large, luminous star, or because it is very close. It is
only possible to use a star’s apparent brightness to determine its distance if you
know the star’s luminosity. Henrietta Leavitt’s work on Cepheids provided the key
to solving this problem.
Question: How do Cepheids allow astronomers to measure intergalactic distances?
1. Collect data: Locate and select the yellow Cepheid variable star (A-091) in the
lower left section of the Andromeda Galaxy. Click the Collect data button. You
will see a graph of the apparent brightness of the star over time.
A. How does the star’s apparent brightness change over time?
Page 3 of 21
Name: ……….. Date: ………
Student Exploration: Big Bang Theory – Hubble’s Law
Vocabulary: absolute brightness, absorption spectrum, apparent brightness, Big
Bang theory, blueshift, Cepheid variable, Doppler shift, Hubble constant, Hubble’s
law, luminosity, megaparsec, period, redshift, spectrograph
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
Standing by the side of a lonely highway at night, you see two motorcycle
headlights, one in each direction. The headlight on your left appears brighter than
the one on your right.
1. If the headlights are equally bright, which motorcycle is closer?
Explain: The motorcycle to your left is closer because the other motorcycle on
the other side of the highway which is farther. This means that whatever side
of the highway you're on, the motorcycle to your left will be closer although
they’re equally bright because the motorcycle on the other side will still be
farther.
2. Suppose the dim-looking headlight on the right is actually a small light on
the front of a bicycle. What can you conclude about the distance of the
motorcycle and bicycle?
They can be farther or closer, but it is hard to tell because the lights are different
from each other.
Gizmo Warm-up
In 1912, an astronomer named Henrietta Swan
Leavitt studied a class of stars called Cepheid
variables. These stars change from bright to dim
to bright again. Her discoveries led to a method
of measuring distances to other galaxies and
eventually helped to support the Big Bang theory
Page 1 of 21
, Page
of the origin of the universe.
Page 2 of 21
, Page
In the Big Bang Theory – Hubble’s Law Gizmo, select Region A. Look at the image of
the Andromeda Galaxy, a galaxy relatively close to our own Milky Way galaxy.
1. Locate the two Cepheid variables, the stars that change in brightness over
time. Star A-091 is the yellow star, and A-171 is the white star.
A. Which star reaches a greater apparent brightness?
I would say the yellow star because it looks brighter. But, it might just be
because yellow is brighter than white.
B. Which star takes longer to
pulse? The yellow star takes
longer to pulse.
2. Because both stars are in the same galaxy, they are about the same distance
from Earth. Based on what you see, how is the brightness of the star related to
how quickly it pulses?
The yellow star is brighter than the white star but it might be because the yellow
star gradually gets brighter. With the white star it brightens really quick.
Get the Gizmo ready:
Activity A:
● On the STARS tab, check that Region A:
Period and
NGC 224 (Andromeda Galaxy) is selected. If
brightness
not, click Return to map and select Region
A.
Introduction: Two factors determine how bright a star appears to an observer: its
luminosity, or absolute brightness, and its distance from the observer. A star may
appear bright because it is a large, luminous star, or because it is very close. It is
only possible to use a star’s apparent brightness to determine its distance if you
know the star’s luminosity. Henrietta Leavitt’s work on Cepheids provided the key
to solving this problem.
Question: How do Cepheids allow astronomers to measure intergalactic distances?
1. Collect data: Locate and select the yellow Cepheid variable star (A-091) in the
lower left section of the Andromeda Galaxy. Click the Collect data button. You
will see a graph of the apparent brightness of the star over time.
A. How does the star’s apparent brightness change over time?
Page 3 of 21
