Measuring the Stars (Part III) The “Cosmic Distance Ladder” Visual “Parallax” “Binocular Vision”… Let’s us “see” 3D images (depth) …but, how to do this to get Astronomical Distances? “Stellar Parallax”… Using Earth’s Orbit as a “Baseline”! “Standard Candles” as Distance Indicators... : (Measured) (Known, “Standard Candle”!) ∝ 2 ( Can now be Calculated !) Main Sequence Stars as Standard Candles! But how to tell apart Main Sequence stars from non-Main-Seq. stars, for Spectroscopic Parallax…? (Both K-type!) Small, Dense (Main Seq.) stars have broader Spectral Lines than “puffy” Giant stars… : Turning “Variable Stars” into Standard Candles for finding distances... : Cepheid “Period-Luminosity Relationship” Faster Rotation More Gravity More Mass More Light (…we assume…!) If (∝ ) now known This Rotating Galaxy is a Standard Candle! White Dwarfs (w/companions) always blow up (“Type Ia Supernova”) at the Chandrasekhar Mass (M = 1.4 x MSun): …Standard Explosion Standard Luminosity Standard Candle! Know Distance to a Supernova Know Distance to its Host Galaxy Can “Map” the Cosmic Large-Scale (Galactic) Structure! Brighter Supernovae glow longer than dimmer Supernovae… Since ~1995, Type Ia Supernovae now have very well known Luminosities… Even better Standard Candles! 1998: Type Ia Supernova Standard Candle data proved that the Expansion Rate of the Universe is Accelerating! 2011 Other Galaxies all Doppler Redshifted… Expanding Universe makes them recede from us! “Hubble’s Law”: V = H0 x D (Velocity = Hubble’s Constant x Distance) Cosmic Distance Mapping the Universe?? Ladder Cosmic Distance Ladder Mapping the Universe!