The distance to the Galactic center inferred from OGLE RR Lyrae variables observed in the direction of the bulge is R _ { 0 } = 8.1 \pm 0.6 kpc .
An accurate determination of R _ { 0 } is hindered by countless effects that include an ambiguous extinction law , a bias for smaller values of R _ { 0 } because of a preferential sampling of variable stars toward the near side of the bulge owing to extinction , and an uncertainty in characterizing how a mean distance to the group of variable stars relates to R _ { 0 } .
A VI -based period-reddening relation for RR Lyrae variables is derived to map extinction throughout the bulge .
The reddening inferred from RR Lyrae variables in the Galactic bulge , LMC , SMC , and IC 1613 match that established from OGLE red clump giants and classical Cepheids .
RR Lyrae variables obey a period-colour ( VI ) relation that is relatively insensitive to metallicity .
Edge-on and face-on illustrations of the Milky Way are constructed by mapping the bulge RR Lyrae variables in tandem with cataloged red clump giants , globular clusters , planetary nebulae , classical Cepheids , young open clusters , HII regions , and molecular clouds .
The sample of RR Lyrae variables do not trace a prominent Galactic bar or triaxial bulge oriented at \phi \simeq 25 \arcdeg .