In the approach to the study of stellar evolution

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In the ______________ approach to the study of stellar evolution, calculations are made from the theory of stellar structure about how stars should change as they contract gravitationally or age through changes in their chemical composition produced by nuclear reactions. : Theoretical. A typical lifetime for a star might be something like ten billion years. The study of the changes and expected changes is then theoretical and based on speculation. In the ________________ approach, stars or groups of stars are observed that are at different stages in their evolution and it is determined whether they actually exhibit the characteristics expected of them from the theoretical predictions. : Observational. The difficulty in the observational approach is that a star ages extremely slowly by human standards and except for those brief periods in its existence where it may be variable or explosive, we do not actually "see" a star evolving. A __________ ________ is a star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size and it believed to be a star near its final stage of evolution. : White dwarf. The predicted mean density of these stars range from about fifty thousand to over one million times that of water. At such densities, matter cannot exist in its usual state. Although it is still gaseous, its atoms are completely stripped of their electrons and the latter are obliged to move according to certain restrictive laws. The matter in white dwarfs is said to be degenerate and this category--approximately ten percent of all stars--are believed to be in the final state of stellar evolution. The ________ ______________ is a sequence of stars on the Hertzsprung-Russell diagram (H-R diagram) containing the majority of stars and they run diagonally from the upper left to the lower right. : Main Sequence. The main sequence is the locus of points on the H-R diagram representing stars of similar chemical composition but different mass. The majority of stars are aligned along this section, approximately ninety percent.
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About 23,000 stars are plotted on the Hertzsprung-Russell diagram to show the relationship between absolute magnitude, luminosity, classification, and the effective temperature of the stars. This diagram shows that stars tend to fall only into certain regions on the diagram. A _____________ is a star of large luminosity and radius. Explanation: Giant. A super giant is a star of very high luminosity. Less than one percent of the stars shown on the H-R diagram are believed to be classified as giant or super giant.
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Astrophysicists typically indicate a star's luminosity by its ___________ ______________, which is the brightness of a star as seen from a distance of 10 parsecs, or 33 light years. Explanation: Absolute Magnitude. This is different from apparent magnitude, which is a star's brightness as seen from Earth.
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In the below diagram, the absolute magnitude runs along the right side. Note that the brighter the star, the lower its magnitude.
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