•Many
different ways of defining distance
–Rulers,
parallax, angular diameter of object of known size, measurement of
apparent brightness of a standard source, radar echo,
etc. All do not
give the same result in cosmological theory.
•Can
write all the distances as d = z/H0+O(z2)
•I
suspect the Hogg et al. article will be clearer than the text…or me.