  Hot Jupiters are a class of extrasolar planet that orbit their parent stars
at very short distances. Due to their close proximity, they are expected to be
tidally locked, which can lead to a large temperature difference between their
day and nightsides. Infrared observations of eclipsing systems have yielded
dayside temperatures for a number of transiting planets. Furthermore the
day-night contrast of the transiting extrasolar planet HD 189733b was mapped
using infrared observations. It is expected that the contrast between the
dayside and nightside of hot Jupiters is much higher at visual wavelengths as
we move shortward of the peak emission, and could be further enhanced by
reflected stellar light. Here we report on the analysis of optical photometric
data of the transiting hot Jupiter CoRoT-1b, which cover 36 planetary orbits.
The nightside hemisphere of the planet is consistent with being entirely black,
with the dayside flux dominating the optical phase curve. This means that at
optical wavelengths the planet's phase variation is just as we see it for the
interior planets in our own solar system. The data allow only for a small
fraction of reflected light, corresponding to a geometric albedo <0.20.
