GIZMOS Student Exploration: Big Bang Theory – Hubble’s Law 2022
(answered)
Name: Saneyah Kendall 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
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 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 star A-171 is the white star.
A. Which star reaches a greater apparent brightness?
ANSWER: Star A-171 is the brighter star.
B. Which star takes longer to pulse?
ANSWER: Star A-091 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?
ANSWER: The brightness of the star is related to how quickly it pulses by
,GIZMOS Student Exploration: Big Bang Theory – Hubble’s Law 2022
(answered)
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?
ANSWER: The star’s brightness kept on going up and down when it changes.
B. Turn on Show time probes. Set the left probe at the first brightness peak, and the
right probe at the second brightness peak. List the time represented by each probe:
Left probe time 1.2
Right probe time 13.5
C. What is the time difference between the two brightness peaks?
ANSWER: The difference is 12.3 between the two brightness peaks.
This difference is the period of the Cepheid.
D. In the DATA tab, record the name of this star and its period.
Do the same on your paper Data worksheet, located on the last page of this document.
(Activity A continued on next page)
, GIZMOS Student Exploration: Big Bang Theory – Hubble’s Law 2022
(answered)
Activity A (continued from previous page)
2. Collect data: The apparent brightness of the star is shown on the y-axis of the graph. The
brightness is given as the ratio of the star’s brightness to the Sun’s brightness if viewed from
a standard distance of one megaparsec (1 Mpc), which is about 3.26 million light years. For
example, a brightness of “4,000” means that the star appears 4,000 times as bright as the
Sun would appear if observed from a distance of 1 Mpc.
A. What is your estimate of the mean apparent brightness of star A-091?
ANSWER: My estimate of the mean apparent brightness is 6500
B. Turn on Show mean brightness. What is the mean brightness of A-091?
ANSWER: 7000
C. In the DATA tab, record this value.
Do the same on your paper Data worksheet, located on the last page of this document.
3. Observe: Stars emit light at a variety of wavelengths. Just as white light is separated into a
rainbow when it passes through a prism, starlight can be separated into its constituent colors
when it passes through an instrument called a spectrograph. The result is a pattern of colors
and black bars called an absorption spectrum. The bars represent wavelengths of light that
are absorbed in the star’s atmosphere. Each star’s unique spectrum depends on the
temperature and composition of its atmosphere.
4. Click Record spectrum to record the star’s spectrum. These will be saved under the Spectra
tab for later use. Look at the spectrum of A-091. Notice the pattern of colors and black bars
in the star’s absorption spectrum.
5. Record: Click Done. Select the other Cepheid variable star in the Andromeda Galaxy (A-
171). Determine and record the period, mean brightness, and spectrum of this star. Then,
click Return to map and select Region B.
There are a total of ten Cepheids hidden in the nine regions of the Gizmo. Record the period,
mean brightness, and spectrum of all ten stars both in the Gizmo data table and on your own
data table.
(Activity A continued on next page)
(answered)
Name: Saneyah Kendall 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
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 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 star A-171 is the white star.
A. Which star reaches a greater apparent brightness?
ANSWER: Star A-171 is the brighter star.
B. Which star takes longer to pulse?
ANSWER: Star A-091 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?
ANSWER: The brightness of the star is related to how quickly it pulses by
,GIZMOS Student Exploration: Big Bang Theory – Hubble’s Law 2022
(answered)
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?
ANSWER: The star’s brightness kept on going up and down when it changes.
B. Turn on Show time probes. Set the left probe at the first brightness peak, and the
right probe at the second brightness peak. List the time represented by each probe:
Left probe time 1.2
Right probe time 13.5
C. What is the time difference between the two brightness peaks?
ANSWER: The difference is 12.3 between the two brightness peaks.
This difference is the period of the Cepheid.
D. In the DATA tab, record the name of this star and its period.
Do the same on your paper Data worksheet, located on the last page of this document.
(Activity A continued on next page)
, GIZMOS Student Exploration: Big Bang Theory – Hubble’s Law 2022
(answered)
Activity A (continued from previous page)
2. Collect data: The apparent brightness of the star is shown on the y-axis of the graph. The
brightness is given as the ratio of the star’s brightness to the Sun’s brightness if viewed from
a standard distance of one megaparsec (1 Mpc), which is about 3.26 million light years. For
example, a brightness of “4,000” means that the star appears 4,000 times as bright as the
Sun would appear if observed from a distance of 1 Mpc.
A. What is your estimate of the mean apparent brightness of star A-091?
ANSWER: My estimate of the mean apparent brightness is 6500
B. Turn on Show mean brightness. What is the mean brightness of A-091?
ANSWER: 7000
C. In the DATA tab, record this value.
Do the same on your paper Data worksheet, located on the last page of this document.
3. Observe: Stars emit light at a variety of wavelengths. Just as white light is separated into a
rainbow when it passes through a prism, starlight can be separated into its constituent colors
when it passes through an instrument called a spectrograph. The result is a pattern of colors
and black bars called an absorption spectrum. The bars represent wavelengths of light that
are absorbed in the star’s atmosphere. Each star’s unique spectrum depends on the
temperature and composition of its atmosphere.
4. Click Record spectrum to record the star’s spectrum. These will be saved under the Spectra
tab for later use. Look at the spectrum of A-091. Notice the pattern of colors and black bars
in the star’s absorption spectrum.
5. Record: Click Done. Select the other Cepheid variable star in the Andromeda Galaxy (A-
171). Determine and record the period, mean brightness, and spectrum of this star. Then,
click Return to map and select Region B.
There are a total of ten Cepheids hidden in the nine regions of the Gizmo. Record the period,
mean brightness, and spectrum of all ten stars both in the Gizmo data table and on your own
data table.
(Activity A continued on next page)
