The Cosmological Distance Ladder. Overlapping rungs: Earth Earth-Mars Earth’s orbit Parallax Spectral “Parallax” RR Lyrae variables Cepheid variables Type I Supernovae Type II Supernovae Galaxy brightness. Measuring Earth - Geometry. = s/r Two wells E-W Measure s Time sun
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Two wells E-W
/2 = t/24 hr
Cayenne (in French Guiana)
This angle was measured simultaneously
If you know the Earth-Mars distance, Kepler’s law
now lets you figure out the radius of Earth’s orbit.
Calculating Earth’s Orbit:
You know that Tan(Ø ) = d/D
Today we have accurate parallaxes for about 10,000 stars.
Since astronomers can
tell by the spectrum of
a star if and where it
falls on the main
sequence, they can get
the absolute magnitude.
If you then measure the
it is a relatively simple process to calculate the
distance to the star: M = m - 5 log10(d/10)
And you know M, and m…