Old-Aged Stellar Population Distance Indicators
  Old-aged stellar distance indicators are present in all Galactic structures
(halo, bulge, disk) and in galaxies of all Hubble types and, thus, are
immensely powerful tools for understanding our Universe. Here we present a
comprehensive review for three primary standard candles from Population II: (i)
RR Lyrae type variables (RRL), (ii) type II Cepheid variables (T2C), and (iii)
the tip of the red giant branch (TRGB). The discovery and use of these distance
indicators is placed in historical context before describing their theoretical
foundations and demonstrating their observational applications across multiple
wavelengths. The methods used to establish the absolute scale for each standard
candle is described with a discussion of the observational systematics. We
conclude by looking forward to the suite of new observational facilities
anticipated over the next decade; these have both a broader wavelength coverage
and larger apertures than current facilities. We anticipate future advancements
in our theoretical understanding and observational application of these stellar
populations as they apply to the Galactic and extragalactic distance scale.
