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E xp an di ng Sp ac e

E xp an di ng Sp ac e. Olber’s Paradox:. In an infinite Universe… Size Age Every line of sight would end on a star. Every star would be observable. The night sky would be very bright. It would be pretty hot too…. Setting the stage:.

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E xp an di ng Sp ac e

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  1. ExpandingSpace

  2. Olber’s Paradox: • In an infinite Universe… • Size • Age • Every line of sight would end on a star. • Every star would be observable. • The night sky would be very bright. • It would be pretty hot too…

  3. Setting the stage: • General relativity predicts that the Universe must be either expanding or contracting. • Einstein thinks it should be static. • Introduces the cosmological constant to keep it static. • Friedmann determines that it still must be dynamic. • Einstein realizes that he is right, and calls the cosmological constant “The greatest mistake of my life”

  4. Meanwhile: • Vesto Slipher at the Lowell Observatory in Flagstaff Arizona measures the red shift of spiral “Nebulae” • The redshift is the Doppler effect • 36 of 40 spiral nebulae are red shifted • Everything is moving away from “us”

  5. Redshift - Doppler Effect If v << c: Δλ=v λ c Moving λ shorter in front λ longer in back (Kinda like a mullet) Sitting still λ same in all directions • Racecars going by • Bell on trains • Example • Java Applet

  6. Put this in your notes: What is the change in wavelength of the 656 nm line of a galaxy receding at 20,000 km/s? What is the new wavelength? 20000E3/3E8*656 = 43.7333 nm 656 + 43.7333 = 699.733 nm 44 nm, 700 nm

  7. What is the recession rate of a galaxy whose 656 nm line comes in at 691 nm? (approximate) (691-656)/656*3E5 = 16,000 km/s 16,000 km/s

  8. Meanwhile: • Edwin Hubble uses the 100 inch telescope on Mt Wilson to look at “spiral nebulae”. • He can pick out individual stars • He finds Cepheids • He calculates the distance to and recession velocity of many galaxies. • There is a relationship

  9. Hubble’s Law: v = Hd H = 71 km/s/Mpc Mpc = Mega parsecs The greater the distance, the greater the recession velocity.

  10. An expanding universe: Before After

  11. An expanding universe:

  12. An expanding universe:

  13. An expanding universe:

  14. An expanding universe:

  15. Put this in your notes: What is the distance to a galaxy that has a 480 nm line that comes in at 497 nm? (Use H = 71 km/s/Mpc ) (497-480)/480*3E5 = 10625 km/s 10625 km/s /(71 km/s/Mpc) = 149.6 Mpc 150 Mpc

  16. What is the recession rate of a galaxy that is 26 Mpc away? (Use H = 71 km/s/Mpc ) 26 Mpc*(71 km/s/Mpc) = 1846 km/s 1846 km/s

  17. What is the distance to the edge of the observable Universe? (Hint: What is the recession velocity if you can no longer see it?) (Use H = 71 km/s/Mpc ) 3E5km/s/(71 km/s/Mpc) = 4225 Mpc 4225 Mpc

  18. What is the distance to a galaxy that has a 480 nm line that comes in at 497 nm? (Use H = 71 km/s/Mpc ) (497-480)/480*3E5 = 10625 km/s 10625 km/s /(71 km/s/Mpc) = 149.6 Mpc 150 Mpc

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