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##### CZ (km/s)

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**CZ**(km/s) Δy Δx Slope = Δy/Δx = H0 D (Mpc) The Hubble Diagram**Redshift**when λo λe Redshift & Blueshift**λo**Absorption lines can be blue-shifted (galaxy is moving toward us) or redshifted (galaxy is moving away). The velocity can be measured by the shift in the wavelength: v = cz = (λo - λe)/λo λe**Standard Candles**A standard candle is an astrophysical object whose absolute magnitude is well known. By comparing the relative intensity of light observed from the object, with that based on its known absolute magnitude, the inverse square law for light intensity can be used to determine the distance to the object. Cepheids & Supernovae**The Inverse Square Law of Light**… relates the absolute luminosity, M of an objectto its apparent luminosity m by m = M / r^2 where r is the distance.**Supernova 1994D**Supernovae**4**Z4 CZ (km/s) 3 Z3 Z2 2 1 Z1 Z0 0 D1 D2 D3 D4 D D0 (Mpc) Original Hubble Diagram**Interpretation**• H4 > H3 Decelerating Universe • H3>H2Decelerating Universe • H2 < H1 Accelerating Universe • H1 < H0 Accelerating Universe H = kilometres per second per Megaparsec**What next?**Cosmological constant or Quintessence?**The Big Rip**At last: proton decay