Three Steps to the Hubble Constant
May 12, 2009
Hubble measurements have simplified the cosmic "distance ladder," which is needed to calculate a more precise value for the universe's expansion rate, called the Hubble constant. At select host galaxies, Cepheid variable stars â€” known as reliable milepost markers â€” are cross-calibrated to Type Ia supernovae in the same host galaxy. The new technique reduced the distance ladder to three "rungs": (1) The distance to galaxy NGC 4258 is measured using straightforward geometry and Kepler's laws; (2) Cepheids in six more distant galaxies are used to calibrate the luminosity of Type Ia supernovae; (3) The Hubble constant is measured by observing a brighter milepost marker, Type Ia supernovae, in more distant galaxies hundreds of millions of light-years away, embedded in the expanding universe.
Topics: Physical cosmology, Standard candles, Astronomy, Type Ia supernova, Galaxy, Hubble Space Telescope, Variable star, Cepheid variable, Hubble's law, Supernova, Cosmic distance ladder, Supernovae