Sp10Name ________________________________Lab Report for Lab #.docx

Sp10Name: ________________________________
Lab Report for Lab #9:Where in the Milky Way Are We?
Part I: The shape of the Milky Way
1. Look up the morphological classification of the Milky Way.
There is a bit more to it than “spiral”. Look for information on
morphological classification in text books and/or online. Find
out the shape of the Milky Way galaxy.
[Type answer here]
2. Identify the parts the Milky Way. Some possible parts of a
galaxy are: bulge, disk, halo, bar, or arm. Knowing the type of
galaxy the Milky Way is, you should be able to identify the
types of features the Milky Way has. Create a physical model of
the Milky Way and identify the features it has. (A globe is an
example of a physical model of Earth.) Describe your model and
label all possible parts.
[Type answer here]
3. Use your planetarium software to observe the Milky Way
from the northern and southern hemispheres. Based on your
observations (without the aid of telescopes or other wavelengths
of light outside the visible range) explain how these
observations support the conclusion that we live in a galaxy
with the shape of your model. Further, determine in what part of
the galaxy the Sun must be located to see the Milky Way as we
do.
[Type answers here]
Part II: Mapping the Milky Way with Globular Clusters
Galaxies like the Milky Way have objects, called “globular
clusters” that exist in the outer regions of the galaxy (or halo).
Globular clusters are dense clusters of stars that are generally
free of gas and dust. In galaxies like the Milky Way, the gas and
dust are located primarily in the disk. If we want to look for

objects that we can see clearly (with no interference from gas
and dust) we must observe objects in the halo. In the late 19th
century an astronomer named Harlow Shapley devised an
experiment to determine the position of Earth in the universe
using globular clusters. He chose these objects because of their
apparent lack of interaction with the gas and dust in the Milky
Way.
Step 4.Explain how Shapley’s experiment could be used to
determine the position of Earth within the Milky Way. Given
what you already know about the part of the galaxy in which the
Sun is located and the information about globular clusters, what
information would Shapley need to figure out the position of
Earth? For about how many globular clusters do you think he
would need to get this information to determine the position of
Earth? Describe the experiment and list the steps one would
need to take.
[Type answers here]
Step 5. As a group, devise a method for determining the
position of Earth within the Milky Way using globular clusters.
Decide how many globular clusters you want to observe. Decide
what information you need to do the analysis. There may be
many different ways of analyzing the data, there does not need
to be group consensus for the analysis, but each method that is
used should be discussed with the group.
[Type answers here]
6. Gather the data you need from sources on the internet. You
may use planetarium software to aid in the identification of
globular clusters. Share the responsibility for gathering data
with every classmate (No one should be exempt from gathering
data.) Each individual class member should analyze the data set
on their own, but gathering the data can be done much more
quickly if everyone gets the data for a number of globular
clusters, and then the data are shared. In fact, this is often how

data are gathered in astronomy since no one individual can get
all the data they need all the time, and certainly not all at once.
[Type answers here]
7. Analyze the data. Use the entire data set gathered by the
class and do the analysis you choose. Determine the position of
Earth within the Milky Way. You should be able to determine
distance from the center of the galaxy and angular position from
some reference point (a measure similar to longitude on the
surface of Earth which is relative to the prime meridian).
[Type answers here]
Step 8.Create a scientific “poster presentation” via whole class
discussion board. Your final product will be a discussion board
presentation. You will need to outline the procedures you used
to gather information (and data), display (upload) or describe
your physical model, show your data, describe your analysis
process and present your result. Compare your results with
known values (use a textbook or some other reliable resource to
check your result). Explain any differences between your result
and the accepted values in terms of the data you used, the
analysis you used and the assumptions you made.
[Type answers here]
Notes:
Students will gather RA and Dec for galactic coordinate data as
well as distances from Earth for a number (at least 25) of
globular clusters. These data will be plotted on an x-y or polar
graph (using Excel or some other graphing software or using
graph paper). Earth’s position is at the center of the graphic.
The center of the Milky Way will be the center of the
distribution of globular clusters plotted.
The following website gives the RA and Dec along with
distance from Sun and from the galactic center:

http://seds.org/~spider/spider/mwgc/mwgc.html.
Page 3 of 3
Where in the Milky Way Are We?
Description:
In the 21st century, most of us are aware that Earth is one of
several planets in our Solar System, which is a system of
planets that orbit a star we call the Sun. The Sun is one of
several hundred billion stars in our Galaxy, which we call the
Milky Way, but where in the Milky Way are we?
At night, all the stars you see are part of the Milky Way. You
may also know that the Milky Way is a spiral galaxy. How
could we find out where Earth and the solar system are located
within this spiral galaxy? This exercise gives students the tools
to design and execute an experiment to determine our location
within the Milky Way.
Introduction:
Figuring out where we are in the universe is an important part
of understanding why we observe what we do. From the
beginning of recorded history, humans have tried to determine
their place in the universe. The ancient Mayans thought that the
universe consisted of Earth, the Sun, the Moon, the planets
(Venus and Mercury) and the stars. Of course, Earth was at the
center of their universe because it did not appear to move.
Separate from Earth were the Sun, the Moon, Venus, Mercury
and the stars.

In the beginning of the 20th century, astronomers began to
realize that the universe was much bigger than previously
thought. This is when astronomers began to understand that we
live in an enormous galaxy that is just one of billions of other
galaxies in the universe. Until this realization, models of the
universe did not go very far beyond the solar system. Most
models assumed that outside the solar system there were stars.
The rest of the universe was just more stars.
Now we know that stars exist primarily within structures known
as galaxies. Galaxies contain stars (from tens of millions in
dwarf galaxies to several trillions in the largest galaxies), gas
and dust. Our Sun is just one of several hundred billion stars in
the Milky Way galaxy. But, like a tree in the forest, it is hard to
tell where we are. Given our history as humans, we would
probably be satisfied with the premise that the Sun must be at
the center of the Milky Way. But, there is observational
evidence to the contrary.
In this exercise, you will determine the (three-dimensional)
shape of the Galaxy and our position within it (or at least,
relative to its center).
Part I: The shape of the Milky Way
1. Look up the morphological classification of the Milky Way.
There is a bit more to it than “spiral”. Look for information on
morphological classification in text books and/or online. Find
out the shape of the Milky Way galaxy.
2. Identify the parts the Milky Way. Some possible parts of a
galaxy are: bulge, disk, halo, bar, or arm. Knowing the type of
galaxy the Milky Way is, you should be able to identify the
types of features the Milky Way has. Create a physical model of
the Milky Way and identify the features it has. (A globe is an
example of a physical model of Earth.)

3. Use your planetarium software to observe the Milky Way
from the northern and southern hemispheres. Based on your
observations (without the aid of telescopes or other wavelengths
of light outside the visible range) explain how these
observations support the conclusion that we live in a galaxy
with the shape of your model. Further, determine in what part of
the galaxy the Sun must be located to see the Milky Way as we
do.
Part II: Mapping the Milky Way with Globular Clusters
Galaxies like the Milky Way have objects, called “globular
clusters” that exist in the outer regions of the galaxy (or halo).
Globular clusters are dense clusters of stars that are generally
free of gas and dust. In galaxies like the Milky Way, the gas and
dust are located primarily in the disk. If we want to look for
objects that we can see clearly (with no interference from gas
and dust) we must observe objects in the halo. In the late 19th
century an astronomer named Harlow Shapley devised an
experiment to determine the position of Earth in the universe
using globular clusters. He chose these objects because of their
apparent lack of interaction with the gas and dust in the Milky
Way.
Step 4.Explain how Shapley’s experiment could be used to
determine the position of Earth within the Milky Way. Given
what you already know about the part of the galaxy in which the
Sun is located and the information about globular clusters, what
information would Shapley need to figure out the position of
Earth? For about how many globular clusters do you think he
would need to get this information to determine the position of
Earth? Describe the experiment and list the steps one would
need to take.
Step 5. As a group, devise a method for determining the
position of Earth within the Milky Way using globular clusters.
Decide how many globular clusters you want to observe. Decide

what information you need to do the analysis. There may be
many different ways of analyzing the data, there does not need
to be group consensus for the analysis, but each method that is
used should be discussed with the group.
6. Gather the data you need from sources on the internet. You
may use planetarium software to aid in the identification of
globular clusters. Share the responsibility for gathering data
with every classmate (No one should be exempt from gathering
data.) Each individual class member should analyze the data set
on their own, but gathering the data can be done much more
quickly if everyone gets the data for a number of globular
clusters, and then the data are shared. In fact, this is often how
data are gathered in astronomy since no one individual can get
all the data they need all the time, and certainly not all at once.
7. Analyze the data. Use the entire data set gathered by the
class and do the analysis you choose. Determine the position of
Earth within the Milky Way. You should be able to determine
distance from the center of the galaxy and angular position from
some reference point (a measure similar to longitude on the
surface of Earth which is relative to the prime meridian).
Step 8.Create a scientific “poster presentation” via whole class
discussion board. Your final product will be a discussion board
presentation. You will need to outline the procedures you used
to gather information (and data), display (upload) or describe
your physical model, show your data, describe your analysis
process and present your result. Compare your results with
known values (use a textbook or some other reliable resource to
check your result). Explain any differences between your result
and the accepted values in terms of the data you used, the
analysis you used and the assumptions you made.
Notes:

Students will gather RA and Dec for galactic coordinate data as
well as distances from Earth for a number (at least 25) of
globular clusters. These data will be plotted on an x-y or polar
graph (using Excel or some other graphing software or using
graph paper). Earth’s position is at the center of the graphic.
The center of the Milky Way will be the center of the
distribution of globular clusters plotted.
The following website gives the RA and Dec along with
distance from Sun and from the galactic center:
http://seds.org/~spider/spider/mwgc/mwgc.html.

Sp10Name ________________________________Lab Report for Lab #.docx

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