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Measuring the Stars (Part III). The “ Cosmic Distance Ladder ”. Visual “ Parallax ”. Let’s us “see” 3D images (depth). “ Binocular Vision”…. …but, how to do this to get Astronomical Distances ?. Using Earth’s Orbit as a “Baseline”!. “ Stellar Parallax” …. “ Standard Candles ”
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Measuring the Stars (Part III)
Visual “Parallax”
Let’s us “see” 3D images (depth) “Binocular Vision”… …but, how to do this to get Astronomical Distances?
Using Earth’s Orbit as a “Baseline”! “Stellar Parallax”…
“Standard Candles” as Distance Indicators... : (Known, “Standard Candle”!) (Measured) ( 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…? Small, Dense (Main Seq.) stars have broader Spectral Lines than “puffy” Giant stars… : (Both K-type!)
Turning “Variable Stars” into Standard Candles for finding distances... : Cepheid “Period-Luminosity Relationship”
FasterRotation MoreGravity MoreMass MoreLight(…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 toaSupernova Know Distance to its Host Galaxy Can “Map” the CosmicLarge-Scale (Galactic) Structure!
Brighter Supernovae glow longer than dimmer Supernovae… Since 1995, Type Ia Supernovae now have very well known Luminosities… Even betterStandard Candles!
1998: Type Ia Supernova Standard Candle data proved that the Expansion Rate of the Universe is Accelerating!
Other Galaxies all Doppler Redshifted… Expanding Universemakes them recede from us! “Hubble’s Law”: V = H0 x D (Velocity = Hubble’s Constant x Distance)