I
First series of U.S. manned spaceflights (1961–63), which began about three weeks after
In May 1961 Alan B. Shepard rode the first Mercury space capsule, Freedom 7, on a 15-minute, 302-mi (486-km) suborbital flight, attaining a maximum altitude of 116 mi (186 km). The first U.S. manned flight in orbit was that of the Friendship 7, carrying John H. Glenn, Jr. , in February 1962; it completed three orbits. The last Mercury flight, Faith 7, launched in May 1963, was the longest, making 22 orbits in about 34 hours.
II
In {{link=Roman religion">Roman religion , the god of merchants, commonly identified with the Greek messenger of the gods, Hermes .
His temple on Rome's Aventine Hill was dedicated in 495 BC. The goddess Maia was identified as his mother, and the two were honoured in a festival on May 15. Mercury is sometimes depicted holding a purse, symbolic of his business functions. More often he is given the attributes of Hermes and portrayed wearing winged sandals or a winged cap and carrying a caduceus .
Mercury, with winged hat and staff, classical statue; in the Uffizi, Florence
Alinari/Art Resource, New York
III
Innermost planet of the solar system .
Its average distance from the Sun is about 36 million mi (58 million km), but its highly elliptical orbit carries it 7.5 million mi (12 million km) nearer to and farther from the Sun. It is the second-smallest major planet (after Pluto), having a diameter of about 3,030 mi (4,880 km) and a mass about one-eighteenth of Earth's. With the shortest period of revolution (only 88 Earth days) and the highest average orbital speed (30 mi/second, or 48 km/second) of any planet, it is aptly named after the fleet-footed Roman messenger god. It spins very slowly, making one complete rotation relative to the stars every 59 Earth days, while its solar day (from one sunrise to the next) is 176 Earth days, owing to its revolution around the Sun. Its surface is heavily cratered. Its most impressive feature is perhaps the 800-mi (1,300-km) Caloris Basin, formed by a huge meteorite impact. Mercury also has steep cliffs that extend for hundreds of miles. The discovery of a magnetic field in its vicinity suggests it has a large iron core, which would account for a mean density almost as high as Earth's. Its atmosphere is negligible; its surface gravity, about one-third that of Earth's, holds an exceedingly tenuous layer of gases. Temperatures at its surface change dramatically, ranging from a high that can exceed 800 kF (425 kC) on the sunward side to a low of about -290 kF (-180 kC) at the end of its night.