Stars and Slopes
- Students will apply the knowledge of plotting data and obtaining a slope
using a log-log coordinate system.
- Students will determine the line of best fit from a set of data
obtained from X-ray astronomy satellites.
- Students will discover the relationship between slope and the
classification of stellar objects.
10th to 12th + grades
Students should have learned the following algebraic concepts:
- graphing a linear equation using slope and y-intercept
- determining a line of best fit from a set of data
- using logarithms
Students should have had an introduction to the concepts of physics
and space astronomy.
For each class of students, you will probably need at least
Many problems in physics, mathematics, engineering, and other fields are
fundamentally the study of the relationship between two variables. For
example, how the velocity of a falling object varies with time; the angular
distribution of radiant energy transmitted from a small hole; the pressure
response frequency characteristic of a crystal telephone receiver. Such
everyday applications involve an independent variable (i.e., one that
progressively changes such as time or frequency) and a dependent variable
which is mathematically determined from the change in the independent variable
in some way (e.g., velocity or intensity).
By displaying the data in a graphic, the relationship of the dependent
variable on the independent variable can be seen. The most powerful form of
display is when the result is a straight line --- which can always be
converted quickly into a mathematical equation. However, obtaining a
straight line curve may require the selection of very special types of graph
paper or axis values.
There are different types of graph paper which can be used for the
presentation of data. They each have their own advantages and disadvantages.
The most common three types are "rectangular" (or "Cartesian") coordinates,
polar coordinates, and logarithmic (or log) coordinates. This lesson will looks
at two of the three -- rectangular and logarithmic.
Day 1 focuses on log-log plotting and determining the slopes of such
Day 2 delves into how to use log-log plots to gain insight into
certain celestial objects of interest to X-ray astronomers.
Day 2 is still under development!
Kaufmann, William J. III, Universe, Freeman and Company, 1994, pgs. 336-340
Kerrod, Robin, Encyclopedia of Science: The Heavens Stars, Galaxies, and
the Solar System, Macmillan Publishing Company, 1991
Kondo, Herbert, The New Book of Popular Science Vol. 1, Grolier
Incorporated, 1982, pgs. 174-190
Overbeck, C.J., Palmer, R.R., Stephenson, R.J., and White, M.W., 1963,
Graphs and Equations, Selective Experiments on Physics, Central Scientific
Seward, Frederick D. and Charles, Philip A., Exploring the X-ray Universe,
Cambridge University Press, 1995
The graphics and other information found within this
lesson can also be found on Imagine the Universe!
which is located on the World Wide Web. The URL for this
The data were retrieved within The HEASARC Data
Archive using W3Browse which is located on the World
Wide Web. The URL for this site is