http://www.ck12.org Chapter 24. Astrophysics
in the core decrease due to the lack of fuel. With the gravitational collapse of the core, the fusion reactions now occur
in a shell surrounding the core. The outer layer of the star expands enormously up to 1000 times the size of the Sun.
When the Sun becomes a red giant, its volume will include the orbit of Mercury and Venus and maybe even Earth.
The increased size increases the luminosity even though the outer layer cools to only 3000 K or so. The cooler outer
layer causes it to be a red star. After a few more million years, the star evolves into a white dwarf-planetary nebula
system.
Summary
The Hertzsprung-Russell diagram (often referred to as the H-R diagram) is a scatter graph that shows various classes
of stars in the context of properties such as their luminosity, absolute magnitude, color, and effective temperature.
Practice
Questions
http://www.youtube.com/watch?v=tt6d9_PQ7TE
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/65435Follow up questions:
- The scales on the HR Diagram are __.
- The spectral class is related to __.
- What color are the stars on the left side of the HR diagram?
Review
Questions
- Which of the following is a reasonable estimate for the surface temperature of the Sun as taken from the HR
diagram?
(a) 10,000 K
(b) 8,000 K
(c) 6,000 K
(d) 4,000 K
(e) 2,000 K - Would the surface temperature of white dwarfs be higher or lower than that of red giants?
(a) higher
(b) lower
(c) could be higher or lower - What is the color of the stars with the highest surface temperature?
(a) blue