Name:_______________________________________________________________ Date:_____________
Partner:___________
Science Connections: How do Scientist use models to learn about the natural world?
In this activity you will use a scientific model astronomers use to determine the types
of stars present in a globular cluster.
Skill Goals:
1) Use a known model, the Hertz-Sprung Russell (HR) Diagram, to determine the
characteristics of stars.
2) Generate HR Diagram of a known star cluster and identify stellar
characteristics using excel
3) Extension: Real Science!
a. Can this model apply to galaxies, a collection of stars?
Common Core Alignment to Standards
•
CCSS.Math.Content.HSF-LE.A.2 Construct linear and exponential functions, including arithmetic and geometric
sequences, given a graph, a description of a relationship, or two input-output pairs (include reading these from a
table).
•
CCSS.Math.Content.HSS-ID.C.8 Compute (using technology) and interpret the correlation coefficient of a linear
fit.
•
CCSS.Math.Content.HSF-LE.B.5 Interpret the parameters in a linear or exponential function in terms of a context.
•
CCSS.Math.Content.HSS-ID.A.3 Interpret differences in shape, center, and spread in the context of the data sets,
accounting for possible effects of extreme data points (outliers).
•
CCSS.ELA-LITERACY.W.9-10.7
Conduct short as well as more sustained research projects to answer a question (including a self-generated
question) or solve a problem; narrow or broaden the inquiry when appropriate; synthesize multiple sources on
the subject, demonstrating understanding of the subject under investigation.
•
CCSS.ELA-LITERACY.W.9-10.8
Gather relevant information from multiple authoritative print and digital sources, using advanced searches
effectively; assess the usefulness of each source in answering the research question; integrate information into
the text selectively to maintain the flow of ideas, avoiding plagiarism and following a standard format for
citation.
•
CCSS.ELA-LITERACY.W.9-10.9
Draw evidence from literary or informational texts to support analysis, reflection, and research.
Materials
Excel
Computer/Laptop
Internet Access
H-R Diagrams
http://lcogt.net/book/h-r-diagrams
Hertzsprung-Russell (HR) Diagrams
In the early 20th century, after investigating
the effects of an object’s temperature and
of the color of its radiation, scientists
reasoned that there should be a
relationship between the temperature of a
star and its luminosity. If all stars were
alike, those with the same luminosity would
have equal temperature and hotter stars
would be brighter than cooler ones.
In 1911, Ejnar Hertzsprung (Denmark),
plotted a graph of star’s magnitudes against
their color. Independently in 1913, Henry
Russell (USA), constructed a plot of stars'
magnitudes against their spectral class,
confirming that indeed, there did seem to
be some sort of relationship between a
star’s luminosity and its temperature, and
the stars fell into distinct groups. Such a
plot was thereafter named the Hetzsprung-Russell or H-R diagrams.
A star on a HR diagram is represented by a dot. Since a large number of stars are usually
represented on a HR diagram, there are a large number of dots on the diagram, as shown below. The
y axis on a HR diagram represents the star’s luminosity and the x axis represents the temperature of
the star (presented by the different in colors B-V).
http://coolwiki.ipac.caltech.edu/index.php/File:Hipall.gif
Luminosity – Absolute Magnitude
Since bright stars can look faint from far away,
or dim stars can look bright if they are close,
astronomers developed a method to find their
true brightness, or absolute magnitude. They
compare how bright they would be if they were
all measured at the same distance. This is
referred to as luminosity, or Absolute
Magnitude.
http://www.skyandtelescope.com/astronomy-resources/the-stellar-magnitude-system/
On the left-hand map of Canis Major, dot sizes indicate stars' apparent magnitudes; the dots match the brightnesses of
the stars as we see them. The right-hand version indicates the same stars' absolute magnitudes — how bright they would
appear if they were all placed at the same distance (32.6 light-years) from Earth. Absolute magnitude is a measure of true
stellar luminosity. Sky & Telescope
Luminosity is how much energy the star exerts. In a physical sense, this is how “bright” the stars are.
The more luminous, the more energy, therefore the brighter the star.
Temperature of a Star
Remember, we cannot go to a star with a thermometer and takes its
temperature. So, how do astronomers find temperature of a very hot object,
billions of miles away? The temperature of a star is found by using
information from a telescope. The temperature of a star can be measured by
find the difference between two colors. When stars are viewed with a
telescope, their colors are record by using filters. With SDSS, the filters are
shown in the table to the right. These all measure the amount of color the
star gives off (measured in the form of a magnitude). When we find the
difference between two colors like b and v, we can find the temperature
based on the principal of blackbody radiation.
Filter
Ultraviolet (u)
Green (g)
Red (r)
Near Infrared (i)
Infrared (z)
Types of Stars on HR Diagram
The main areas of a HR diagram are labelled above and are briefly described below for stars of about
the same mass as our Sun (solar mass stars):
Main sequence
The main sequence is
a band which stretches
from the bottom right
of the HR diagram up
to the top left, hence it
goes from cooler,
dimmer stars up to
brighter, hotter ones.
Most stars, including
our Sun spend most of
their lives on the main
sequence as they fuse
their Hydrogen into
Helium in their cores.
Red Giant Branch
Once solar mass stars
have fused all their
Hydrogen into Helium,
they evolve off the
main sequence into the Red Giants area (which astronomers call the Red Giant branch or RGB). At
this point, the Hydrogen shell surrounding the core of the star begins to burn, producing even more
Helium.
Red Supergiants
When the Hydrogen shell burning is finished, the shell of Helium begins fusing into heavier elements
such as Carbon and Oxygen. As this happens, the star moves into the Red Supergiants region of the
HR diagram.
White Dwarfs
Once all the Helium has been fused into other elements, the outer layers of the star are ejected
outwards into what is known as a planetary nebula. The exposed core of the star (made up of Carbon
and Oxygen) which is leftover, is a white dwarf. A white dwarf cannot keep the fusion going and
gradually becomes fainter and cooler. Evolution from the red supergiant area to the white dwarf area,
happens very quickly in comparison to how long the star stayed on the main sequence.
A sample H-R diagram with temperature on the x-axis and luminosity on the y-axis*
http://skyserver.sdss3.org/public/en/astro/stars/stars.aspx
An H-R diagram showing the evolutionary track of a sun-like star*
http://skyserver.sdss3.org/public/en/astro/stars/stars.aspx
Part I – Creating an HR Diagram
Selecting hundreds of stars can be very time consuming. Astronomers have developed program and tools to select
multiple objects. We will use one of these tools to generate a HR plot of Palomar 5 and use it to determine stars.
1) Click this link: http://skyserver.sdss3.org/dr10/en/tools/search/sql.aspx
2) Erase the content in the white box.
3) Copy and paste this into the white box and press submit:
select
s.objid, s.ra, s.dec, s.u, s.g, s.r, s.i, s.z
from
star s, dbo.fGetNearbyObjEq(229.0128,-0.1082,3) n
where
s.objid = n.objid
4) Copy and paste the data into excel on a new spread sheet. There is about ~700 stars on this plot so it may take a few
extra seconds to load the data. Tip: Copy and Paste from bottom to top. It seems to work better.
5) Save your work as Lastname_Palomar 5 HR_5_31_14
6) We need to find the color (Temperature) of the stars. We can do that by finding the difference in colors magnitudes.
Generate a new column called g-r
7) We will let excel do the calculations for us. Type into the cell beneath the title “g-r”
=E2-F2
And then press ENTER. This includes the equal sign. The equal sign tells excel to make a numerical calculation.
This will calculate the difference for us.
8) Click on the lower right box and drag the box all the way down to calculate the difference of all the values.
9) Now its time to plot your graph. You will plot the “r” magnitude on the y-axis and the “g-r” magnitude on
the x-axis.
a. Insert Scatter Plot
b. Right click on scatter plot
c. “Select Data”
d. “Add”
e. Click the button next to the “Series x”. Highlight the x values
f. Click the button next to the “Series y”. Highlight the y values
g. Select OK
h. Select OK
10) In order to make your graph look like the model, you must reverse the both axis. To do this, right click on
one of the axis
a. Format Axis
b. Select “Values in Reverse Order”
Analysis
1) Analyze your graph using the HR Model.
a. Circle and label the main sequence. How many stars are on the main sequence?
b. What kind of stars are present?
i. Circle and label sections of stars
c. What kind of stars are missing?
d. If your teacher instructs, share you data with another group and compare.
2) Is this a new or old star cluster based on the stellar evolution chart? Explain and site your evidence.
Part II – What type of stars are in the Palomar Cluster?
11) Open Link: http://skyserver.sdss3.org/dr10/en/tools/chart/navi.aspx?ra=229.0128&dec=-0.1082
12) Use the mouse to click on a star. A green box should appear around the star as seen on the screen below.
13) Click “Add to Notes” to record the data from that star.
14) Repeat this process for ~30 stars. Use the magnifying glass to find faint stars. Be sure to choose stars only in
the cluster.
15) Click “Show Notes” when you are done collecting the data.
16) At the bottom of the page, click Export and select CSV. This will transport the data into an excel file.
17) Open and Save your excel file. In the next free column, type the heading “g-r”. This will determine the
color/temperature of your star.
18) To reduce calculations we will let excel do the calculations for us. Type into the cell beneath the title “g-r”
=F2-G2
And then press ENTER. This includes the equal sign. The equal sign tells excel to make a numerical calculation.
You can also select the two cells as well. This will calculate the difference for us.
19) Select the tiny box in the bottom right corner, hold, and extend the box all the way down your data set.
20) When you let go of the mouse, the values should automatically be calculated.
21) Now its time to plot your graph. You will plot the “r” magnitude on the y-axis and the “g-r” magnitude on
the x-axis.
a. Insert Scatter Plot
b. Right click on scatter plot
c. “Select Data”
d. “Add”
e. Click the button next to the “Series x”. Highlight the x values
f. Click the button next to the “Series y”. Highlight the y values
g. Select OK
h. Select OK
22) In order to make your graph look like the model, you must reverse the both axis. To do this, right click on
one of the axis
a. Format Axis
b. Select “Values in Reverse Order”
23) Use the “Vertical” and “Horizontal” Cross axis to move the axis to the left of your screen.
24) Play with the scaling to generate the signature slope of the HR Diagram, down and to the right.
Analysis
3) Analyze your graph using the HR Model.
a. How many stars are on the main sequence?
b. What kind of stars are present?
c. What kind of stars are missing?
d. If your teacher instructs, share you data with another group and compare.
i. Share your graph using your google-accounts. Share document with instructor.
Extensions
1) Find different star clusters to work with and generate their HR Plots.
 Palomar 3 - 151.382,0.071

Use the HR for galaxies. Does the model also work for stars in galaxies?
o Galaxy Cluster 1 - 29.071,1.051
o Galaxy Cluster 2 - 213.601,-0.378
Extra Resources for Learning:

Color – Temperature
http://phet.colorado.edu/sims/blackbody-spectrum/blackbody-spectrum_en.html

H-R Diagram Activity

http://skyserver.sdss3.org/public/en/proj/advanced/hr/simplehr.aspx
Teacher Guide for More Projects
http://skyserver.sdss3.org/public/en/proj/teachers/teachershome.aspx