ASTR 1102 002 2008 Fall Semester Joel E Tohline Alumni Professor Office 247 Nicholson Hall Slides from Lecture19 Chapter 23 Our Galaxy and Chapter 24 Galaxies Schematic Illustration of Our Milky Way Galaxy Real All Sky Images of Our Milky Way Galaxy Aside Atomic transition that gives rise to 21 cm radiation which is used by astronomers to map out the distribution of neutral hydrogen throughout our Galaxy and other galaxies is also the physical principle underlying the MRI magnetic resonance imaging diagnostic tool in modern medicine Medical MRI Determining Size of MW Galaxy We have not always known that the diameter of our Galaxy is 50 kpc as illustrated in following slide Herschel s map of our Galaxy 1785 based on star counts Thin disk not much more than 1 kpc across Sun approximately at center of disk Determining Size of MW Galaxy We have not always known that the diameter of our Galaxy is 50 kpc as illustrated in following slide Herschel s map of our Galaxy 1785 based on star counts Thin disk not much more than 1 kpc across Sun approximately at center of disk Determining Size of MW Galaxy We have not always known that the diameter of our Galaxy is 50 kpc as illustrated in following slide For example Herschel s map of our Galaxy 1785 based on star counts Thin disk not much more than 1 kpc across Sun approximately at center of disk Herschel s Map of MW Galaxy Determining Size of MW Galaxy We have not always known that the diameter of our Galaxy is 50 kpc as illustrated in following slide For example Herschel s map of our Galaxy 1785 based on star counts Thin disk not much more than 1 kpc across Sun approximately at center of disk Herschel s map grossly distorted by interstellar extinction Prominent and Obscured Objects Shapley s View of MW Galaxy Look out of the plane of the MW disk to minimize obscuration due to interstellar extinction Distribution of Globular Clusters not symmetric about Sun s location Distances to GCs obtained using RR Lyrae variable stars as standard candles Shapley s View of MW Galaxy Look out of the plane of the MW disk to minimize obscuration due to interstellar extinction Distribution of Globular Clusters not symmetric about Sun s location Distances to GCs obtained using RR Lyrae variable stars as standard candles Shapley s View of MW Galaxy Look out of the plane of the MW disk to minimize obscuration due to interstellar extinction Distribution of Globular Clusters not symmetric about Sun s location Distances to GCs obtained using RR Lyrae variable stars as standard candles Shapley s View of MW Galaxy Look out of the plane of the MW disk to minimize obscuration due to interstellar extinction Distribution of Globular Clusters not symmetric about Sun s location Distances to GCs obtained using RR Lyrae variable stars as standard candles Determining Distances in Astronomy Stellar parallax Spectroscopic parallax main sequence fitting Remember distance modulus m M 5 log d 5 If you know M for a certain type of star then a measurement of m gives you d Standard candles Identifiable stars for which you know M Determining Distances in Astronomy Stellar parallax Spectroscopic parallax main sequence fitting Remember distance modulus m M 5 log d 5 If you know M for a certain type of star then a measurement of m gives you d Standard candles Identifiable stars for which you know M Determining Distances in Astronomy Stellar parallax Spectroscopic parallax main sequence fitting Remember distance modulus m M 5 log d 5 If you know M for a certain type of star then a measurement of m gives you d Standard candles Identifiable stars for which you know M Determining Distances in Astronomy Stellar parallax Spectroscopic parallax main sequence fitting Remember distance modulus m M 5 log d 5 If you know M for a certain type of star then a measurement of m gives you d Standard candles Identifiable stars for which you know M Determining Distances in Astronomy Stellar parallax Spectroscopic parallax main sequence fitting Remember distance modulus m M 5 log d 5 If you know M for a certain type of star then a measurement of m gives you d Standard candles Identifiable stars for which you know M Determining Distances in Astronomy Stellar parallax Spectroscopic parallax main sequence fitting Remember distance modulus m M 5 log d 5 If you know M for a certain type of star then a measurement of m gives you d Standard candles Identifiable stars for which you know M Example Standard Candles RR Lyrae variables Pulsation period of about day Luminosity is 100 x solar luminosity Sun M 4 8 let s call it M 5 for simplicity RR Lyrae M 0 Population I Cepheid variables Luminosities range up to 10 000 solar M 5 Pulsation period luminosity correlation Type Ia supernovae Luminosity 3 x 109 solar Example Standard Candles RR Lyrae variables Pulsation period of about day Luminosity is 100 x solar luminosity Sun M 4 8 let s call it M 5 for simplicity RR Lyrae M 0 Population I Cepheid variables Luminosities range up to 10 000 solar M 5 Pulsation period luminosity correlation Type Ia supernovae Luminosity 3 x 109 solar Example Standard Candles RR Lyrae variables Pulsation period of about day Luminosity is 100 x solar luminosity Sun M 4 8 let s call it M 5 for simplicity RR Lyrae M 0 Population I Cepheid variables Luminosities range up to 10 000 solar M 5 Pulsation period luminosity correlation Type Ia supernovae Luminosity 3 x 109 solar Example Standard Candles RR Lyrae variables Pulsation period of about day Luminosity is 100 x solar luminosity Sun M 4 8 let s call it M 5 for simplicity RR Lyrae M 0 Population I Cepheid variables Luminosities range up to 10 000 solar M 5 Pulsation period luminosity correlation Type Ia supernovae Luminosity 3 x 109 solar Example Standard Candles RR Lyrae variables Pulsation period of about day Luminosity is 100 x solar luminosity Sun M 4 8 let s call it M 5 for simplicity RR Lyrae M 0 Population I Cepheid variables Luminosities range up to 10 000 solar M 5 Pulsation period luminosity correlation Type Ia supernovae Luminosity 3 x 109 solar Example Standard Candles RR Lyrae variables Pulsation period of about day Luminosity is 100 x solar luminosity Sun M 4 8 let s call it M 5 for simplicity RR Lyrae M 0 Population I Cepheid variables Luminosities range up to 10 000 solar M 5 Pulsation period luminosity correlation Type Ia supernovae Luminosity 3 x 109 solar Example Standard Candles RR Lyrae variables Pulsation period of about day Luminosity is 100 x solar luminosity Sun M 4 8