The Detailed Optical Light Curve of GRB 030329

(Abridged) We present densely sampled BVRI light curves of the opticaltransient associated with the gamma-ray burst GRB 030329, the result of acoordinated observing campaign conducted at five observatories. Augmented withpublished observations of this GRB, the compiled optical dataset contains 2687photometric measurements, obtained between 78 minutes and 79 days after theburst. We show that the underlying supernova 2003dh evolved faster than, andwas probably somewhat fainter than the type Ic SN 1998bw, associated with GRB980425. We find that our data can be described by a broken power-law decayperturbed by a complex variable component. The early- and late-time decayslopes are determined to be ~1.1 and ~2, respectively. Assuming this singlepower-law model, we constrain the break to lie between ~3 and ~8 days after theburst. This simple, singly-broken power-law model, derived only from theanalysis of our optical observations, may also account for available multi-banddata, provided that the break happened ~8 days after the burst. The morecomplex double-jet model of Berger et al. provides a comparable fit to theoptical, X-ray, mm and radio observations of this event. We detect asignificant change in optical colors during the first day. Our color analysisis consistent with a cooling break frequency sweeping through the optical bandduring the first day. The light curves of GRB 030329 reveal a rich array ofvariations, superposed over the mean power-law decay. We find that the earlyvariations are asymmetric, with a steep rise followed by a relatively slower(by a factor of about two) decline. The variations maintain a similar timescale during the first four days, and then get significantly longer.