Mapping Globular Clusters
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School
University of Texas, Permian Basin *
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Course
1101.701
Subject
Astronomy
Date
Apr 3, 2024
Type
Pages
4
Uploaded by ChiefMask13618
Mapping Globular Clusters
In this lab, our goal is to measure the distance from the Sun to the center of the Milky Way
Galaxy. Finding the center of the galaxy is surprisingly difficult. It’s a bit like trying to find the
center of a forest while you are wandering in and among the trees. Fortunately, the ancient star
clusters known as “globular clusters” provide an avenue for us to solve this problem.
Globular clusters are evenly distributed around the center of a galaxy. They are also easy to
identify in the night sky. Astronomers have discovered many globular clusters and carefully
measured their distances. By graphing the location of these globular clusters, we can determine
the precise location of the center of our galaxy. Below is a table of globular clusters and their (x,
y) distance as measured from our solar system.
Cluster
x (kpc)
y (kpc)
NGC 104
3.79
-5.22
NGC 362
5.21
-8.47
NGC 1851
6.13
-12.85
NGC 2808
2.28
-10.53
NGC 3201
0.97
-7.79
NGC 4372
4.54
-7.71
NGC 4590
4.79
-8.44
NGC 5286
9.00
-10.15
NGC 5927
5.24
-3.46
NGC 6101
7.48
-6.18
Complete the instructions below and answer the reflection questions.
1.
Put a star at (0,0) on the graph below. This will represent the location of our sun.
Remember that our sun is
not
located at the center of the galaxy. (Has it been a while
since you graphed data like this? Watch
this brief teacher video
for review.)
2.
Using the data above, mark the location of each globular cluster on the graph below.
(Here are a few options for how to do this: 1) You can print this document and graph by
hand, 2) You can draw your own version of the graph with pencil and paper and graph
the data, or 3) You can insert data points
using the draw tool in Google Docs
. )
3.
Since globular clusters are distributed evenly around the center of a galaxy, finding the
approximate center of a group of globular clusters will allow us to determine the center
of the galaxy itself. Estimate the center of the globular clusters on the graph below. Mark
this location (which represents the galactic center) using a different color pen and record
its x and y location in the table below.
x (kpc)
y (kpc)
Galactic
Center
4.
Next we will calculate the straight-line distance from the Sun to the Galactic Center. You
can perform this calculation with the “
Pythagorean Theorem
” below, or you can simply
use this “
Galactic Center Distance Calculator
” that I created for you. How many
kiloparsecs is the Sun from the Galactic Center?
One kiloparsec (kpc) is 3,260 lightyears. So, we can calculate how many lightyears it is to
the galactic center by taking the distance in kpc (above) and multiplying by 3,260.
Perform this calculation. How many lightyears is the sun from the center of our galaxy?
To calculate the distance from the Sun to the center of our galaxy in light-years, we need
to know the precise value of the distance in kiloparsecs (kpc). As of my knowledge cutoff
in September 2021, the estimated distance from the Sun to the center of the Milky Way
galaxy is approximately 8.2 kiloparsecs.
To convert this distance to light-years, we can multiply it by the conversion factor you
provided:
8.2 kpc * 3,260 light-years/kpc = 26,732 light-years.
Therefore, based on this calculation, the Sun is estimated to be approximately 26,732
light-years away from the center of our galaxy.
5.
If you were an astronomer, how would you improve this data set in order to make an
even better measurement of the distance to the center of the galaxy?
As an astronomer, there are several ways I could improve the data set to make a better
measurement of the distance to the center of the galaxy. Here are a few possible
approaches:
1.
High-precision Distance Indicators: I would utilize more accurate and precise distance
indicators to measure the distances to celestial objects in the galaxy. For example, I
could employ methods such as Cepheid variable stars, Type Ia supernovae, or RR Lyrae
stars, which have well-established relationships between their intrinsic luminosity and
period or color. By identifying and studying these objects in the galaxy, we can obtain
more reliable distance measurements.
2.
Parallax Measurements: I would conduct more parallax measurements of nearby stars.
Parallax is the apparent shift in the position of a star due to the Earth's orbit around the
Sun. By observing the positions of nearby stars from different points in Earth's orbit, we
can determine their distances with great accuracy. Increasing the number of stars with
precise parallax measurements would provide additional data points for calculating the
distance to the center of the galaxy.
3.
Redshift Mapping: I would perform a detailed redshift mapping of the galaxy's structure.
Redshift is the shift in the wavelength of light emitted by distant objects due to the
expansion of the universe. By analyzing the redshift of galaxies at different locations
within our galaxy, we can map out its large-scale structure and identify regions that are
closer or farther from the galactic center. This information would be crucial in refining
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distance calculations.
Globular Cluster Graph
If drawn by hand, be sure to scan (or take a picture of) your completed graph and include it in
this document.
Completing the Lab
●
Submit your completed lab document using
your instructor’s online dropbox
.
●
Return to the course and complete the
lab quiz
to demonstrate your understanding.