The crew of the International Space Station (ISS) has trimmed an evergreen for the Christmas season. The X-mas tree and gifts were delivered to the ISS by the space shuttle Endeavor well in advance, said Sergei Puzanov, NASA Coordinator for Public Relations at the Russian Mission Control Center. Yet, the astronauts on board the ISS did not open up the gifts until Christmas Eve, he pointed out. The men had a joyous celebration last night. Russia's Yuri Onufrienko, commander of the crew, and the United States' Carl Walz both boast beautiful voices, so the two of them delivered an impromptu concert on the station, Puzanov said. On Christmas Day, which is a day-off at the ISS, the crewmembers have been able to speak with their families via a radio & television bridge. The astronauts spent the last few days unloading the Russian cargo spacecraft Progress, which had delivered to the ISS fuel, water, air, and food. On taking over from the 3rd long-time expedition in mid-December, the new crew continued monitoring the ISS life-support systems, controlling levels of radiation in the station's working and residential compartments, and doing medical research.