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Chapter 20 Galaxies Determining Distance

Chapter 20 Galaxies Determining Distance. Measuring distances to galaxies:. We measure galaxy distances using a chain of interdependent techniques. Step 1 Determine size of solar system using radar – because light travels at a constant speed in space. Step 2

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Chapter 20 Galaxies Determining Distance

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  1. Chapter 20Galaxies Determining Distance

  2. Measuring distances to galaxies: We measure galaxy distances using a chain of interdependent techniques

  3. Step 1 Determine size of solar system using radar – because light travels at a constant speed in space

  4. Step 2 Use parallax to determine distance of nearby stars out to a few hundred light-years

  5. Use cluster distance to determine the luminosity of each type of star within it & plot them on an HR diagram

  6. Step 3 Calculate distance of more distant clusters by comparing their brightness to nearby clusters.

  7. Step 4 Cepheid variables are very luminous stars that have a period-luminosity relationship. We can use these stars as standard candles.

  8. Visible UV X-Ray Supernova 2005ke Image Credit: NASA A standard candle = an object whose luminosity we can determine without measuring its distance.

  9. Cepheid variable stars with longer periods have greater luminosities

  10. Step 5 Use white dwarf (type Ia) supernovae as standard candle. All WD have the same maximum mass of 1.4 Ms. Therefore they all have the same luminosity. Apparent brightness tells us distance to galaxies up to 10 billion light-years

  11. Step 6 Tully-Fisher Relation Use entire galaxies as standard candles because luminosity is related to rotation speed (both depend on mass)

  12. Lastly, use redshift. Hubble measured the distance to the Andromeda Galaxy using Cepheid variables as standard candles Edwin Hubble

  13. He measured redshift & distance to other galaxies

  14. Hubble found that redshift and distance are related in a special way Hubble’s Law: velocity = H0 x distance

  15. Distances of farthest galaxies are measured from redshifts

  16. Hubble’s constant tells us age of universe because it relates velocities and distances of all galaxies Age = ~ 1 / H0 Distance Velocity

  17. But distances between faraway galaxies change while light travels Astronomers think in terms of lookback time rather than distance distance?

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