What is 1 - the diamonds in the diagram. The near stars are...

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What is a ``Typical'' Star? The Sun is often said to be an ``average'' or ``typical'' middle-aged star. What is ``average'' depends on how you choose your sample! 1. Compared to the nearby stars, the Sun is luminous, hot, and big. 2. Compared to the apparently bright stars, the Sun is dim, cool, and small. 3. Compared to the stars in globular clusters, the Sun is very young. 4. Compared to the stars in open (galactic) clusters, the Sun is very old. If you picked stars at random from our galaxy, what would they tend to look like? How the stars are selected can give you very different answers of what a typical star is like. The figure below shows where the 100 apparently brightest stars in our sky would be plotted and where the 100 nearest stars would be plotted on the H-R diagram. Both data sets are from the Hipparcos survey. The stars that appear bright in our sky also are intrinsically luminous for the most part. They are
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Unformatted text preview: the diamonds in the diagram. The near stars are all within 7.63 parsecs of the Sun. They are plotted with the upside-down triangles. A great majority of the near stars are cool and faint. Another way to compare them is to plot the proportions of the spectral types for each group. As shown in the figure below, most of the apparently bright stars are the hot and luminous A and B-type stars. The sample includes a few of the very hot O-type stars. All but one of the K-type stars in the bright star sample are giants or supergiant stars. All of the M-type stars are giants or supergiants. The graph for the near star sample looks very different: the majority of stars are the cool and faint K and M-type stars. Only one star in the entire sample is a giant star. The rest are main sequence stars....
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What is 1 - the diamonds in the diagram. The near stars are...

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