Milky way galaxy ppt

ppt on milky way galaxy and approximately how old is the milky way galaxy
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Prof.EvanBaros,United Kingdom,Teacher
Published Date:26-07-2017
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Chapter 23 The Milky Way GalaxyUnits of Chapter 23 23.1 Our Parent Galaxy 23.2 Measuring the Milky Way XXEarly “Computers” 23.3 Galactic Structure 23.4 The Formation of the Milky Way 23.5 Galactic Spiral Arms XXDensity Waves 23.6 The Mass of the Milky Way Galaxy 23.7 XXThe Galactic Center23.1 Our Parent Galaxy From Earth, we see few stars when looking out of our galaxy (red arrows) and many stars when looking in (blue arrows). Milky Way is what our galaxy appears as in the night sky.23.1 Our Parent Galaxy Our galaxy is a spiral galaxy. The Andromeda Galaxy, our closest spiral neighbor, probably resembles the Milky Way fairly closely.23.1 Our Parent Galaxy Here are two other spiral galaxies, one viewed from the side and the other from the top:23.2 Measuring the Milky Way One of the first attempts to measure the Milky Way was done by Herschel using visible stars. Unfortunately, he was not aware that most of the galaxy, particularly the center, is blocked from view by vast clouds of gas and dust.23.2 Measuring the Milky Way We have already encountered variable stars—novae, supernovae, and related phenomena. There are other stars whose luminosity varies in a regular way, but much more subtly. These are called intrinsic variable stars. Two types of intrinsic variables have been found: RR Lyrae stars and Cepheids.23.2 Measuring the Milky Way The upper plot is an RR Lyrae star. All such stars have essentially the same luminosity curve with periods from 0.5 to 1 day. The lower plot is a Cepheid variable; Cepheid periods range from about 1 to 100 days.23.2 Measuring the Milky Way The variability of these stars comes from a dynamic balance between gravity and pressure—they have large oscillations around stability.23.2 Measuring the Milky Way The usefulness of these stars comes from their period–luminosity relation:23.2 Measuring the Milky Way This allows us to measure the distances to these stars: • RR Lyrae stars all have about the same luminosity; knowing their apparent magnitude allows us to calculate the distance. • Cepheids have a luminosity that is strongly correlated with the period of their oscillations; once the period is measured, the luminosity is known and we can proceed as above.23.2 Measuring the Milky Way We have now expanded our cosmic distance ladder one more step:23.2 Measuring the Milky Way Many RR Lyrae stars are found in globular clusters. These clusters are not all in the plane of the galaxy, so they are not obscured by dust and can be measured. This yields a much more accurate picture of the extent of our galaxy and our place within it.23.3 Galactic Structure This artist’s conception shows the various parts of our galaxy, and the position of our Sun:23.3 Galactic Structure The galactic halo and globular clusters formed very early; the halo is essentially spherical. All the stars in the halo are very old, and there is no gas and dust. The galactic disk is where the youngest stars are, as well as star formation regions— emission nebulae and large clouds of gas and dust. Surrounding the galactic center is the galactic bulge, which contains a mix of older and younger stars.23.3 Galactic Structure Stellar orbits in the disk move on a plane and in the same direction; orbits in the halo and bulge are much more random.23.4 The Formation of the Milky Way Any theory of galaxy formation should be able to account for all the properties below:23.4 The Formation of the Milky Way The formation of the galaxy is believed to be similar to the formation of the solar system, but on a much larger scale:23.5 Galactic Spiral Arms Measurement of the position and motion of gas clouds shows that the Milky Way has a spiral form:23.5 Galactic Spiral Arms The spiral arms cannot rotate at the same speed as the galaxy; they would “curl up”.

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