The Hubble constant.

Five methods of estimating distances have demonstrated internal reproducibility at the level of 5-20% rms accuracy. The best of these are the cepheid (and RR Lyrae), planetary nebulae, and surface-brightness fluctuation techniques. Luminosity-line width and Dn-sigma methods are less accurate for an individual case but can be applied to large numbers of galaxies. The agreement is excellent between these five procedures. It is determined that Hubble constant H0 = 90 +/- 10 km.s-1.Mpc-1 [1 parsec (pc) = 3.09 x 10(16) m]. It is difficult to reconcile this value with the preferred world model even in the low-density case. The standard model with Omega = 1 may be excluded unless there is something totally misunderstood about the foundation of the distance scale or the ages of stars.

已有五种距离估算方法被证明具备5%~20%均方根（rms）精度的内部重现性。其中性能最优的方法包括造父变星（Cepheid）与天琴座RR型变星（RR Lyrae）法、行星状星云法以及表面亮度起伏法。光度-线宽法与Dn-σ法在单案例中的测算精度稍显不足，但可应用于大规模星系样本的分析。上述五种方法的测算结果吻合度极佳。经测算，哈勃常数（Hubble constant）H₀ = 90 ± 10 km·s⁻¹·Mpc⁻¹ [1秒差距（parsec, pc）= 3.09×10¹⁶ m]。即便在低密度宇宙模型的框架下，该数值也难以与学界主流的宇宙学模型相匹配。除非距离尺度的基础理论或恒星年龄的相关认知存在完全未被探明的误区，否则Ω=1的标准宇宙模型或将被排除。