  We report discovery of a luminous F-type post-asymptotic-giant-branch (PAGB)
star in the Galactic globular cluster (GC) M79 (NGC 1904). At visual apparent
and absolute magnitudes of V=12.20 and Mv=-3.46, this "yellow" PAGB star is by
a small margin the visually brightest star known in any GC. It was identified
using CCD observations in the uBVI photometric system, which is optimized to
detect stars with large Balmer discontinuities, indicative of very low surface
gravities. Follow-up observations with the SMARTS 1.3- and 1.5-m telescopes
show that the star is not variable in light or radial velocity, and that its
velocity is consistent with cluster membership. Near- and mid-infrared
observations with 2MASS and WISE show no evidence for circumstellar dust. We
argue that a sharp upper limit to the luminosity function exists for yellow
PAGB stars in old populations, making them excellent candidates for Population
II standard candles, which are four magnitudes brighter than RR Lyrae
variables. Their luminosities are consistent with the stars being in a PAGB
evolutionary phase, with core masses of ~0.53 Msun.
  We also detected four very hot stars lying above the horizontal branch
("AGB-manqu'e" stars); along with the PAGB star, they are the brightest objects
in M79 in the near ultraviolet. In an Appendix, we give periods and light
curves for five variables in M79: three RR Lyrae stars, a Type II Cepheid, and
a semiregular variable.
