Uncertainties in Cepheid Determined Distances
Chief among the uncertainties tied to the Classical and Type II Cepheid distance scale are: the nature of the period-luminosity relation in various passbands, the impact of metallicity on both the zero-point and slope of those relations, and the effects of photometric contamination (blending) and a changing (typically unknown) extinction law on Cepheid distances. All these topics are actively debated in the literature.
These unresolved matters have resulted in cited values for the Hubble constant (established from Classical Cepheids) ranging between 60 km/s/Mpc and 80 km/s/Mpc. Resolving this discrepancy is one of the foremost problems in astronomy since the cosmological parameters of the Universe may be constrained by supplying a precise value of the Hubble constant.
Read more about this topic: Cepheid Variable
Famous quotes containing the words determined and/or distances:
“Patriotism having become one of our topicks, Johnson suddenly uttered, in a strong determined tone, an apophthegm, at which many will start: “Patriotism is the last refuge of a scoundrel.” But let it be considered that he did not mean a real and generous love of our country, but that pretended patriotism which so many, in all ages and countries, have made a cloak of self-interest.”
—Samuel Johnson (1709–1784)
“I was surprised by Joe’s asking me how far it was to the Moosehorn. He was pretty well acquainted with this stream, but he had noticed that I was curious about distances, and had several maps. He and Indians generally, with whom I have talked, are not able to describe dimensions or distances in our measures with any accuracy. He could tell, perhaps, at what time we should arrive, but not how far it was.”
—Henry David Thoreau (1817–1862)