Name: Date: 7-11-2020
Student Exploration: Big Bang Theory – Hubble’s Law
absolute brightness, absorption spectrum, apparent brightness, Big Bang theory,
Vocabulary
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 These
variables.
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 of the origin of the universe.
, 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.
Activity A: Get the Gizmo ready:
● On the STARS tab, check that Region A: NGC
Period and
224 (Andromeda Galaxy) is selected. If not, click
brightness
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?
The star is really bright at the very beginning (first 3 days) then gradually decreases
the amount of luminosity. On the 12th day it begins to get brighter and peaks on the
thirteenth day.
Student Exploration: Big Bang Theory – Hubble’s Law
absolute brightness, absorption spectrum, apparent brightness, Big Bang theory,
Vocabulary
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 These
variables.
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 of the origin of the universe.
, 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.
Activity A: Get the Gizmo ready:
● On the STARS tab, check that Region A: NGC
Period and
224 (Andromeda Galaxy) is selected. If not, click
brightness
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?
The star is really bright at the very beginning (first 3 days) then gradually decreases
the amount of luminosity. On the 12th day it begins to get brighter and peaks on the
thirteenth day.
