Assignment 6.pdf - Rowan Introduction to Astronomy Activity...

Rowan Introduction to Astronomy
Activity #6:
Properties of Stars: The Hertzsprung-Russell Diagram
Name: _______________________________________________ Score: ____________________________________
 Acknowledgement
This activity is adapted from “ The Life Cycles of Stars ” developed for Project ASTRO NOVA by the Planetarium at
Raritan Valley Community College (The New Jersey Astronomy Center for Education at Raritan Valley Community
College, Somerville, NJ 08876 – 1265).
 Objective
Students learn about these important properties shared by all stars: luminosity (brightness), temperature, and color.
 Background
 In the early 20
th
century (around 1910), Swedish astronomer Ejnar Hertzsprung and American astronomer Henry
Norris Russell plotted the colors (temperatures) of stars against their luminosities (or brightness).
 The resulting graph represented a huge leap forward in understanding stellar evolution, or the “ lives of stars. ”
 The color and temperature of stars are usually plotted on the x- axis, with high temperatures to the left and low to the
right. All temperatures are given in K, or Kelvin degrees.
 Luminosity (usually plotted on the vertical or y- axis) is given in terms of the Sun’s luminosity (either multiples or a
fractional part). Sometimes luminosity is replaced by the absolute magnitude of the star.
 Celestial objects appear in a vast range of brightness. For example our Sun appears 16 trillion times brighter than the
faintest stars visible to the naked eye. Clearly, some other means of expressing astronomical brightness is needed.
 Astronomers have developed what is called the magnitude scale : a logarithmic scale in which a difference of
exactly 5 magnitudes corresponds to a factor of 100 in brightness. Each magnitude corresponds to a factor of 2.512
in brightness because 2.512 × 2.512 × 2.512 × 2.512 × 2.512 = 100. The magnitude scale runs from large positive
numbers for very faint objects to negative numbers for very bright objects. For example a star of magnitude 5 is 100
times fainter than a star of magnitude 0. A star of magnitude − 1 is 2.512 times brighter than a star of magnitude 0.