  We combine long-term photometric observations in multiple band passes to
determine the rotational light curve for the binary Kuiper-Belt object (79360)
Sila-Nunam. We measure an unambiguous fundamental period of 6.2562 +/- 0.002 d,
within 0.02% of half the orbital period (Porb = 12.50995 +/- 0.00036 d)
determined earlier from HST observations resolving the binary. The light curve
is double-peaked, and well fit by the sum of two sinusoids: a primary with
period Porb/2 and peak-to-peak amplitude 0.120 +/- 0.012 mag and a secondary
with period Porb and peak-to-peak amplitude 0.044 +/- 0.010 mag. Excluding
observations within ~0.1 deg of opposition, we measure a linear solar phase
dependence with slope 0.147 +/- 0.018 mag deg-1 and a mean absolute magnitude
in the Gunn g band of 6.100 +/- 0.006 mag. There is no rotational color
variation exceeding 4%. We also observe that eclipses occur centered on light
curve minima to within 0.3%, requiring the long axis of at least one of the two
bodies to point precisely toward the other. Assuming the binary is doubly
synchronous and both rotation axes are aligned with the orbital angular
momentum vector, our observations jointly constrain triaxial shape models for
Sila and Nunam such that the product of their long-to-intermediate axes ratios
is 1.120 +/- 0.01. Hence both bodies are elongated by 6%, or else one is
elongated by 6% to 12%, and the other by less than 6%.
