Chapter 10: Measuring the Stars A plot of some of the brighter stars as discussed in table 10.2 This diagram is called the H-R diagram after the inventors Hertzsprung and Russell. It is a plot of spectral type (temperature) verses Luminosity (intrinsic brightness).

Chapter 10: Measuring the Stars This is a plot for stars within 5 pc of the Sun. Most of the stars lie along the shaded region called the main sequence. This is where Hydrogen is being burned by the stars. The dashed lines represent different sizes of stars.

Chapter 10: Measuring the Stars This is a plot of the 100 brightest stars. Most of them are larger than the Sun and several are located off the main sequence.

Chapter 10: Measuring the Stars Now that we can deduce the luminosity of a star based on its color, we can use this information to determine distances to other stars.

Chapter 10: Measuring the Stars Binary stars are important because they allow us to measure the mass of stars if we know their separation by using Kepler’s third law p 2  a 3. We can separate the stars visually or we can use a combination of Doppler effect and eclipsing binaries to deduce both size and mass.

Chapter 10: Measuring the Stars When we map the mass of stars on the HR diagram we get the following graph. Note that the brighter, hotter stars are also the most massive.

Chapter 10: Measuring the Stars Bigger stars burn hotter and brighter, but have shorter lives.

Chapter 10: Measuring the Stars Star cluster are important to study because the stars were born at the same time, out of the same material, and are at the same distance. Thus, any differences we see are the result of intrinsic differences and not distance. Here is a HR diagram of a young, open star cluster.

Chapter 10: Measuring the Stars Here is a HR diagram of an old, globular star cluster. Notice the lack of big, bright, hot stars. They have aged and evolved off of the main sequence.