Distance ladder so far:

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Review from last time
Distance ladder so far

• Get AU from Keplers 3rd and radar
• Get nearby stars from parallax
• Use standard candles, e.g. Cepheid variables
  (be careful of population)
• Other standard candles...

M f(Period)
know M somehow
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If you know L and can measure f you can solve for
d.
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From Nick Strobels Astronomy Notes
Interesting historical paradox
Solution??
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Back to distance determination and using stellar
color ..
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B V is larger when the temperature is cooler
B magnitude smaller (object brighter)
B magnitude larger (object fainter)
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Hertzsprung-Russell Diagram
Luminosity vs. color or temperature
More luminous
Less luminous
cooler
hotter
In many cases, the stars themselves can be used
as standard candles, once the HR-diagram is
calibrated. But need to know it is a main
sequence star.
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Hertzsprung-Russel diagram for an young cluster
No giants
Main Sequence
No white dwarfs
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Hyades Open cluster Constellation Taurus
Magnitude 0.5 Angular size 330
Pleides Open cluster Constellation Taurus
Magnitude 1.6 Angular size 110
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Age 800 million years
Age 65 million years
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If the cluster is highly evolved and most of the
massive stars are gone, one can still use that
portion of the main sequence that remains
unburned.
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Other distance indicators
(very uncertain)
- relates L of a galaxy to its rotation rate
absolute magnitude
rotational speed
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(inaccurate, not used much)
Considered the best today.
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SN 1998dh
SN 1998aq
SN 1998bu
Type Ia supernovae are the biggest thermonuclear
explosions in the universe. Twenty billion,
billion, billion megatons. For several weeks
their luminosity rivals that of a large galaxy.
HST
SN 1994D
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The width of the light curve is correlated with
its peak luminosity. Brighter Broader This
relation, known as the Philipps
relation exists because both the brightness and
width are correlated with the amount of
radioactivity (56Ni) each supernova makes. Using
this correlation, much of the spread in the
observations can be narrowed.
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Hubble
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From Nick Strobels Astronomy Notes
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v Ho d
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• But other measures are consistent
• with 12 14 billion years.
• Globular cluster ages
• Radioactive dating of the elements

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H constant only in the absence of
deceleration
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T 2.7249 2.7251 K
A picture of the universe when it was only
379,000 years old
(WMAP 2003)
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As of 2003