  We report the detection of a transiting Jupiter-sized planet orbiting a
relatively bright (V=11.79) K0V star. We detected the transit light-curve
signature in the course of the TrES multi-site transiting planet survey, and
confirmed the planetary nature of the companion via multicolor photometry and
precise radial velocity measurements. We designate the planet TrES-1; its
inferred mass is 0.75 +/- 0.07 Jupiter masses, its radius is 1.08 (+0.18/-0.04)
Jupiter radii, and its orbital period is 3.030065 +/- 0.000008 days. This
planet has an orbital period similar to that of HD 209458b, but about twice as
long as those of the OGLE transiting planets. Its mass is indistinguishable
from that of HD 209458b, but its radius is significantly smaller and fits the
theoretical models without the need for an additional source of heat deep in
the atmosphere, as has been invoked by some investigators for HD 209458b.
