  We present the results of a 5 month photometric time-series survey for
stellar rotation over a 40'x40' field on the 150 Myr open cluster M35. We
report rotation periods for 441 stars and determine their cluster membership
and binarity based on a decade-long radial-velocity survey, proper-motion
measurements, and multi-band photometric observations. We find that 310 of the
stars with measured rotation periods are late-type members of M35. Their
distribution of rotation periods span more than two orders of magnitude from
~0.1-15 days, not constrained by the sampling frequency and the time-span of
the survey. With an age between the zero-age main-sequence and the Hyades, and
with ~6 times more rotation periods than measured in the Pleiades, M35 permit
detailed studies of early rotational evolution of late-type stars. Nearly 80%
of the 310 rotators lie on two distinct sequences in the color-period plane,
defining clear relations between stellar rotation period and color (mass). The
M35 color-period diagram enables us to determine timescales for the transition
between the two rotational states for G and K dwarfs, respectively. These
timescales are inversely related to the mass of the convective envelope, and
offer constraints on the rates of internal and external angular momentum
transport and of the evolution of stellar dynamos. A comparison to the Hyades,
confirm the Skumanich (1972) spindown-dependence for G dwarfs on one rotational
state, but suggest that K dwarfs spin down more slowly. The locations of the
rotational sequences in the M35 color-period diagram support the use of
rotational isochrones to determine ages for coeval stellar populations. We use
such gyrochronology to determine "gyro-ages" for M35. We use the M35 data to
evaluate new color dependencies for the rotational isochrones.

Astrophysics