Freedman, W. L. et al. (2001), «Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant», Astrophysical Journal553: 47, Bibcode:2001ApJ...553...47F, doi:10.1086/320638.
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Freedman, W. L. et al. (2001), «Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant», Astrophysical Journal553: 47, Bibcode:2001ApJ...553...47F, doi:10.1086/320638.