a. Clusters of stars are useful because they share: age, composition, and same distance from usa. Pleiadesi. All stars formed around same timeii. The differences in luminosities mean something: the more intrinsically brighter stars in that clustera. Absence of main sequence stars; red giant region presentb. Relatively OLDc. In our Milky Way galaxy, these globular clusters reside in the “halo” region of the galaxy.d. No high mass stars; the more massive the star is the shorter its life, therefore these stars are older.a. The Sun is bigger because the core is burning at higher temperatures (hotter core = bigger Sun)b. As core temperature rises, the star is getting biggeri. Following the H-R diagram, as the temperature is going down because size is larger, it goes off the main sequences and shoots off to the red giant region.c. One it becomes a red giant, it lives like that for a while.ASTRON 89 1nd Edition Lecture 21Outline of Last Lecture I. The Interstellar Medium: Consists Gas and DustII. ISM gas is very DIFFUSEIII. Nebula is a general term used for fuzzy objects in the skyOutline of Current Lecture I. Star clusters all form at approximately the same time, because when one star forms it triggers the formation of others Reflection NebulaeII. Open cluster III. Globular clusterIV. Evolution of a Sun-like StarCurrent LectureI. Star clusters all form at approximately the same time, because when one star forms it triggers the formation of others Reflection Nebulaea. Clusters of stars are useful because they share: age, composition, and same distance from usb. Which is important for inverse square law, which tells us their relative LUMINOSITIES, because if they’re all the same distance, then luminosity is comparable among the stars in that cluster. And therefore their size! More massive = more luminous and less massive = less luminousII. Open cluster a. Pleiadesi. All stars formed around same time ii. The differences in luminosities mean something: the more intrinsically brighter stars in that cluster b. All stars in that cluster are young because they are still living on the main sequenceIII. Globular clusterThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. Absence of main sequence stars; red giant region present b. Relatively OLD c. In our Milky Way galaxy, these globular clusters reside in the “halo” region of the galaxy.d. No high mass stars; the more massive the star is the shorter its life, therefore these stars are older.e. There are some main sequence stars.IV. Evolution of a Sun-like Stara. The Sun is bigger because the core is burning at higher temperatures (hotter core= bigger Sun)b. As core temperature rises, the star is getting bigger i. Following the H-R diagram, as the temperature is going down because size is larger, it goes off the main sequences and shoots off to the red giant region.c. One it becomes a red giant, it lives like that for a while. d. Despite its cooler Temperature, its luminosity goes up because it is just hugee. Electron Degeneracy i. When sun leaves main sequence it becomes red giant because of H shell burning around a He core, and becomes 100 times its size. The Helium flash occurs. He burns vigorously into C, creating a C core. C now is not burning, core of C shrinks because gravity takes over. Pushes shell around it to get hotter and it burns from He to C adding more C to core, shell around He burns from H to He. It goes back up to red giant branch after second puff of the