Determining the Hubble constant Hubble's law

value of hubble constant including measurement uncertainty recent surveys.

the value of hubble constant estimated measuring redshift of distant galaxies , determining distances same galaxies (by other method hubble s law). uncertainties in physical assumptions used determine these distances have caused varying estimates of hubble constant.

earlier measurement , discussion approaches

for of second half of 20th century value of




h

0




{\displaystyle h_{0}}

estimated between 50 , 90 (km/s)/mpc.

the value of hubble constant topic of long , rather bitter controversy between gérard de vaucouleurs, claimed value around 100, , allan sandage, claimed value near 50. in 1996, debate moderated john bahcall between sidney van den bergh , gustav tammann held in similar fashion earlier shapley-curtis debate on these 2 competing values.

this wide variance in estimates partially resolved introduction of Λcdm model of universe in late 1990s. Λcdm model observations of high-redshift clusters @ x-ray , microwave wavelengths using sunyaev-zel dovich effect, measurements of anisotropies in cosmic microwave background radiation, , optical surveys gave value of around 70 constant.

more recent measurements planck mission indicate lower value of around 67.

see table of measurements above many recent , older measurements.

acceleration of expansion

a value



q


{\displaystyle q}

measured standard candle observations of type ia supernovae, determined in 1998 negative, surprised many astronomers implication expansion of universe accelerating (although hubble factor still decreasing time, mentioned above in interpretation section; see articles on dark energy , Λcdm model).