AST 115 1st Edition Lecture 28 Outline of Last Lecture I. White dwarf starsa. PropertiesII. Stellar explosions: observations of phenomenaa. Planetary nebulab. Novac. SupernovaIII. Post-main sequence for high mass and very high mass starsIV. Stellar explosions: explanations and phenomenaa. White dwarf and planetary nebulab. Novac. Supernova Type Iad. Supernova Type IIe. Supernova 1987aV. Supernova remnants and the Crab NebulaVI. PulsarsVII. Black HolesOutline of Current Lecture I. Introduction to Chapter 13 – The Galaxiesa. Milky WayII. Structure of the GalaxyThese 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.III. Populations in the Galaxya. Population Ib. Population IIIV. The Sun’s location in the GalaxyV. The true nature of the “Nebulae”a. CatalogsVI. The Great Spiral Nebula in AndromedaVII. The Great Spiral Galaxy in AndromedaCurrent LectureIntroduction to Chapter 13 – The Galaxies Milky Way = the irregular band of faint white light that encircles the entire inside of the celestial sphere. o (it is brighter is the direction of the summer night sky) What is the significance of this observation about the structure of the Galaxy?...o We are in a flat, disk-shaped Galaxy. We are positioned between the middle and the edge of our Galaxy. Structure of the Galaxyo Flat, wheel-shaped disko ~ 100,000 LY diametero Spherical, concentric halo, a few hundred thousand LY diametero Central bulge is ~ 20,000 LY in diameter Populations in the Galaxyo Two general categories, or populations, of objects in the Galaxy based on their chemical makeup and location. Population I: Disk component.- Helium, Hydrogen, and a small amount of heavier elements. Population II: Old halo component- Only contain hydrogen and heliumo The Sun is a member of Population I. The Sun’s location in the Galaxyo In the disko At ~ 26,000 LY or ~ ½ of the way out from the center of the Galaxyo Disk at most is ~ 2,000 LY thick.o This was determined by Harlow Shapley using the RR Lyrae Variable stars in the globular star clusters. Says that the center of the Galaxy is associated with the concentration of globular star clusters. The concentration of these star clusters is displacedfrom the location of the Sun; therefore, the Sun is not at the center of theGalaxy. The true nature of the “Nebulae”o Messier 51 “The Whirlpool” (sketched by Lord Rosse in the mid-1800’s) It is a nebulao Catalogs of Nebulas The Messier Catalog: “M numbers” NGC = New General Catalog (J.L.E. Dreyer) The Great Spiral Nebula in Andromedao Messier Catalogue (M31)o New General Catalog (NGC 224)o M31 looks like a cotton ball in small telescopes.o Hubble’s distance to M31: Cepheid variable stars can be recognized by:- Spectra- Regular cycle of brightness variation- Some are bright enough to see at distances of 10s of millions of LY. The Period-Luminosity Relation:- Discovered by Henrietta Leavitt early in the 20th century. - “The longer the period of brightness variation that a Cepheid has, the more luminous it is.” The Great Spiral Galaxy in Andromedao d = 2,500,000
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