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To stress this point further, the apparent magnitudes of stars within a single cluster can be used to compare luminosities among those stars: The lower the apparent magnitude number of a star in a certain cluster, the greater the luminosity compared to all of the other stars. This is due to the fact that the distance between individual stars in a cluster is much, much less than the distance the cluster is from Earth. The distance between the front and back edges of the cluster simply does not significantly affect the apparent magnitudes of the stars of a cluster, making the differences in the luminosities of the stars the overriding cause of the different apparent magnitudes. If a star in a cluster appears brighter to us compared to another star in the same cluster, then the brighter star must have a higher luminosity. Earth to cluster Cluster edge to edge Figure 1

To stress this point further, the apparent magnitudes of stars within a single cluster can be used to compare luminosities among those stars: The lower the apparent magnitude number of a star in a certain cluster, the greater the luminosity compared to all of the other stars. This is due to the fact that the distance between individual stars in a cluster is much, much less than the distance the cluster is from Earth. The distance between the front and back edges of the cluster simply does not significantly affect the apparent magnitudes of the stars of a cluster, making the differences in the luminosities of the stars the overriding cause of the different apparent magnitudes. If a star in a cluster appears brighter to us compared to another star in the same cluster, then the brighter star must have a higher luminosity. Earth to cluster Cluster edge to edge Figure 1

Applications and Investigations in Earth Science (9th Edition)
Applications and Investigations in Earth Science (9th Edition)
9th Edition
ISBN:9780134746241
Author:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Publisher:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Chapter1: The Study Of Minerals
Section: Chapter Questions
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To stress this point further, the apparent magnitudes of stars within a single cluster can be used to compare luminosities among those stars: The lower the apparent magnitude number of a star in a certain cluster, the greater the luminosity compared to all of the other stars. This is due to the fact that the distance between individual stars in a cluster is much, much less than the distance the cluster is from Earth. The distance between the front and back edges of the cluster simply does not significantly affect the apparent magnitudes of the stars of a cluster, making the differences in the luminosities of the stars the overriding cause of the different apparent magnitudes. If a star in a cluster appears brighter to us compared to another star in the same cluster, then the brighter star must have a higher luminosity. Finding the turn-off color-index of a star cluster We are finally ready to turn to the object of interest: color-magnitude diagrams, or CMDs for short. A CMD, such as the one to the right, is a plot of all of the stars in a cluster, but with a very specific set of axes. Along the horizontal axis is the color-index of each star, and along the vertical axis is the apparent magnitude of each star. Note that the vertical axis is reversed: the values for apparent magnitude get smaller as you go up. Pause a moment to look at the CMD to make sure you note each of these features. Earth to cluster Every point on a CMD represents exactly one star. We can read off a star's B-V value by extending an imaginary vertical line down from the star to the horizontal axis. We can read off a star's apparent magnitude by extending an imaginary horizontal line left from the star toward the vertical axis. B. Which star is more luminous? 14 74 16 18 20 22 0 Cluster edge to edge For practice (be sure to check your results with your instructor to make sure you got them right): A. Using the CMD in figure 2, estimate the B-V values of stars X and Y. Star X: X 0.5 B-V Figure 1 Y Star Y: C. Assuming both X and Y are on the main sequence and were born at the same time, which star will leave the main sequence first? Explain your answer. 1.5 Figure 2
Transcribed Image Text:To stress this point further, the apparent magnitudes of stars within a single cluster can be used to compare luminosities among those stars: The lower the apparent magnitude number of a star in a certain cluster, the greater the luminosity compared to all of the other stars. This is due to the fact that the distance between individual stars in a cluster is much, much less than the distance the cluster is from Earth. The distance between the front and back edges of the cluster simply does not significantly affect the apparent magnitudes of the stars of a cluster, making the differences in the luminosities of the stars the overriding cause of the different apparent magnitudes. If a star in a cluster appears brighter to us compared to another star in the same cluster, then the brighter star must have a higher luminosity. Finding the turn-off color-index of a star cluster We are finally ready to turn to the object of interest: color-magnitude diagrams, or CMDs for short. A CMD, such as the one to the right, is a plot of all of the stars in a cluster, but with a very specific set of axes. Along the horizontal axis is the color-index of each star, and along the vertical axis is the apparent magnitude of each star. Note that the vertical axis is reversed: the values for apparent magnitude get smaller as you go up. Pause a moment to look at the CMD to make sure you note each of these features. Earth to cluster Every point on a CMD represents exactly one star. We can read off a star's B-V value by extending an imaginary vertical line down from the star to the horizontal axis. We can read off a star's apparent magnitude by extending an imaginary horizontal line left from the star toward the vertical axis. B. Which star is more luminous? 14 74 16 18 20 22 0 Cluster edge to edge For practice (be sure to check your results with your instructor to make sure you got them right): A. Using the CMD in figure 2, estimate the B-V values of stars X and Y. Star X: X 0.5 B-V Figure 1 Y Star Y: C. Assuming both X and Y are on the main sequence and were born at the same time, which star will leave the main sequence first? Explain your answer. 1.5 Figure 2
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