A105 Stars in addition to Galaxies Today’s APOD Announcements Kirkwood Obs. open Weds night 6:30-8:30 PM Rooftop Session on Thurs, Nov. 16 @ 8 PM

A105 Stars in addition to Galaxies Today’s APOD Announcements Kirkwood Obs. open Weds night 6:30-8:30 PM Rooftop Session on Thurs, Nov. 16 @ 8 PM www.phwiki.com

A105 Stars in addition to Galaxies Today’s APOD Announcements Kirkwood Obs. open Weds night 6:30-8:30 PM Rooftop Session on Thurs, Nov. 16 @ 8 PM

Hayes, Sherron, News Director has reference to this Academic Journal, PHwiki organized this Journal A105 Stars in addition to Galaxies This week’s units: 74, 75, 76, 78, 79 News Quiz Today Galaxies homework due Thursday Projects due Nov. 30 Today’s APOD Announcements Kirkwood Obs. open Weds night 6:30-8:30 PM Rooftop Session on Thurs, Nov. 16 @ 8 PM Leonid Meteor Shower, Friday AM or PM Main Types of Galaxies Spirals Ellipticals Irregulars

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Hubble Deep Field Our deepest images of the universe show a great variety of galaxies, many of them billions of light-years away Irregular Galaxies Hubble Ultra Deep Field Spiral Galaxy Elliptical Galaxy Elliptical Galaxy Spiral Galaxy disk bulge halo

Spheroidal Component: bulge & halo, old stars, few gas clouds Disk Component: stars of all ages, many gas clouds Disk Component: stars of all ages, many gas clouds Spheroidal Component: bulge & halo, old stars, few gas clouds Blue-white color indicates ongoing star as long as mation Red-yellow color indicates older star population Properties of Elliptical Galaxies Round or elliptical in shape Contain no visible gas or dust No young stars or star- as long as ming regions The largest galaxies are ellipticals ( in addition to also some of the smallest)

Elliptical Galaxy: All spheroidal component, virtually no disk component Red-yellow color indicates older star population Properties of Irregular Galaxies Chaotic mix of stars, gas in addition to dust No bulge or spiral arms May contain star as long as ming regions Usually small galaxies Blue-white color indicates ongoing star as long as mation Classifying Galaxies Elliptical Spiral Irregular

Classifying Galaxies Elliptical Spiral Irregular Thought Question Why does ongoing star as long as mation lead to a blue-white appearance A. There aren’t any red or yellow stars B. Short-lived blue stars outshine others C. Gas in the disk scatters blue light Famous Galaxies! The Local Group – about 3 dozen galaxies Milky Way Large in addition to Small Magellanic Clouds Andromeda M33 Dwarfs About four times smaller than our Milky Way Galaxy Near M31 more than twice the angular size of the full moon visible with a good pair of binoculars Messier 33

The Whirlpool Messier 51 23 million light years away Messier 87 Giant elliptical galaxy at the center of the Virgo Cluster of galaxies ~60 million light years away note globular clusters jet other galaxies Messier 82 About 12 Mly very disturbed galaxy

The Mice ~ 300 Mly The Puzzle of “Spiral Nebulae” Be as long as e Hubble, some scientists argued that “spiral nebulae” were entire galaxies like our Milky Way, while others maintained they were smaller collections of stars within the Milky Way The debate remained unsettled until someone finally measured their distances How did Hubble prove that galaxies lie far beyond the Milky Way St in addition to ard C in addition to les! Pulsating Stars Hubble settled the debate by measuring the distance to the Andromeda Galaxy using Cepheid variables as st in addition to ard c in addition to les

Cepheid Variable Stars Because the period of a Cepheid variable star tells us its luminosity, we can use these stars as st in addition to ard c in addition to les Period = 3 days Cepheid variable stars with longer periods have greater luminosities The Nearest Stars Determine distances of stars out to a few hundred light-years using parallax Distances

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Distances of Galaxies Galaxies are too far away as long as parallax technique Use “st in addition to ard c in addition to les” (INVERSE SQUARE LAW) Cepheid variable supergiant stars planetary nebulae supernovae Image “graininess” – The smoother the distribution of stars in a galaxy the farther away it is Steps to the Distance Scale How do astronomers measure distances to objects Brightness alone does not provide enough in as long as mation to measure distance Start with nearby objects, move to greater distances Identifying the Main Sequence Apparent brightness of star cluster’s main sequence tells us its distance

Knowing a star cluster’s distance, we can determine the luminosity of each type of star within it, including the distances to Cepheids Establishing the brightness of stars Other Distance Methods What clues give you in as long as mation about distance

Read Units 74, 75, 76, 78, 79 Galaxies homework due Thurs

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