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Purpose: To illustrate
how HR diagrams of star clusters are used to determine the distances and ages of
the clusters. If desired, students can also measure the magnitudes and colors of
the cluster stars using a simulated telescope, thus learning how astronomers
collect the data used to produce an HR diagram.
H-R Diagrams of Star Clusters, is the first in a series of
exercises using its Virtual Educational Observatory (VIREO). Using real
photometric data from a variety of sources, students are able to access
databases of V magnitudes and B-V colors, as well as positions for stars in a
variety of clusters of differing ages and distances. Students can load this data
directly into display software, and can view the clusters in the VIREO optical
telescope. They can, if desired, measure the apparent magnitudes of the stars
themselves using simulated telescopes equipped with photometers and CCD Cameras,
and store the data for later analysis. Data analysis software, which draws on an
extensive database of theoretical isochrones, allows students to fit HR diagrams
to models. Students are thus able to determine distance modulus, reddening, and
ages of the clusters. The exercise includes a student workbook with brief
background information on stellar evolution, along with instructions on the use
of the software.
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Clea
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The HR
Diagram exercise utilizes the Virtual Educational Observatory Software,
Click Filename to Download (using left mouse button to "Save Link As") 
