Measuring the Stars
(Part III)
The “Cosmic Distance Ladder”
“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... :
“Standard Candle”!)

( 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
 Even better Standard Candles!
1998: Type Ia Supernova Standard Candle data proved that
the Expansion Rate of the Universe is Accelerating!
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??
Cosmic Distance Ladder  Mapping the Universe!

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