Three Steps to the Hubble Constant
Three Steps to the Hubble Constant
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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 – known as reliable milepost markers – 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.


Tags
Cosmology, Dark Energy, Dark Matter, Distant Galaxies, Exotic, Hubble Telescope, Illustrations, Universe Age/Size

Credits

Credit: NASA, ESA, and A. Feild (STScI)