Distance Ladders
Astronomical Unit - 150 million km, is basic unit of distance.
Leads directly to the parsec (~ 3.26 lightyears) through parallax measurements.
Measure distances to local stars through direct geometric (parallax) measurements.
Well done from space - eg Hipparcos. Will do more in the future.
In exceptional circumstances (eg Maser stars), we can get rare direct measurements to more distant objects.
Can get an estimate on distance to the galactic center.
NB NGC 4258 as key rung.
Standard Candles: espcially Cepheids.
Period-Luminosity relation. (NB RR Lyrae).
get distance to nearby galaxies - Hubble key project.
Secondary calibrators: Tully-Fisher, Faber-Jackson, surface brightness fluctuation, Planetary Nebular luminosity function.
Type Ia supernova.
Detonation of almost constant mass of fuel of almost constant composition - can correct for small variation.
Visible for billions of light years, as luminous as entire galaxies at peak.
Gives distance calibration to redshift greater than 1.
Hubble constant - calibrated on Cepheids in the local universe.
H0 = 72 km/sec/Mpc
Type Ia supernovae calibrate change in Hubble constant over time.
Oh, we see recession - galaxies are almost all moving away from us, further away they are, the faster they recede
you all knew that. Quick review of z = v/c for v << c and v = H0*d
THIS IS AN IMPORTANT FORMULA
Last updated 01/08
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