The observed angular diameter of a source depends on the curvature of
spacetime (i.e. the cosmology). For a fixed linear diameter
D_{l}:

where z is the redshift, H_{o} is the Hubble constant,
and q_{o} is the deceleration parameter. Typical values
are H_{o} = 70 km/s/Mpc and q_{o} = 0.5.

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