Four US astronauts who were pioneers in space exploration are due to be awarded a top civilian honor -- the Congressional Gold Medal -- in a ceremony on Capitol Hill on Wednesday. Neil Armstrong, 81, who was the first man to walk the Moon, and his colleague Buzz Aldrin, 81, who was the second, are among the honorees. Also receiving the medals are Michael Collins, also 81, who was the command module pilot for Apollo 11, the first manned mission to the Moon in 1969, and former senator John Glenn, 90, the first American to orbit the Earth in 1962. The ceremony is set for 11:00 am (1600 GMT) at the US Capitol Rotunda. Past winners of the Congressional Gold Medal, described as the \"highest expression of national appreciation for distinguished achievements and contributions,\" include Myanmar pro-democracy icon Aung San Suu Kyi, the Dalai Lama, Walt Disney and Pope John Paul II. The Congressional Gold Medal is the US Congress\'s highest expression of national appreciation for distinguished achievements and contributions. The Presidential Medal of Freedom is considered the nation\'s highest civilian honor.