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We present deep CCD photometry of the globular cluster M13 (NGC 6205) in theStromgren uvby-Beta system, and determine a foreground reddening of E(b-y)=0.015mag. From a fit to the main-sequence of metal-poor subdwarfs withHipparcos parallaxes, we derive (m-M)_0=14.38 +- 0.10 which implies an age near12 Gyr assuming [Fe/H]=-1.61 and [Alpha/Fe]=0.3. The distance independent((b-y)_0, c_0) diagram indicates that M13 and metal-poor field subdwarfs ofsimilar metallicity must be coeval to within +-1 Gyr. In addition, we findthat, at any given (b-y)_0 color, there is a large spread in the c_0 index forM13 red-giant branch (RGB) stars. We suspect that this scatter, which extendsat least as faint as the base of the RGB, is most likely due to star-to-starvariations in the atmospheric abundances of the CNO elements. We also note theexistence of what appears to be two separate stellar populations on the HB ofM13. Among other possibilities, it could arise as the result of differences inthe extent to which deep mixing occurs in the precursor red giants.Comment: 14 pages, including two encapsulated postscript figures. Accepted for  publication in ApJL, Uses aasms4.st

Strömgren Photometry of Globular Clusters: The Distance and Age of M13, Evidence for Two Populations of Horizontal-Branch Stars