United States Army Materiel Command. The U.S. Army Materiel Command (AMC) is the primary provider of materiel to the United States Army. The Command's mission includes the research & development of weapons systems as well as maintenance and parts distribution.
A comet is a small, icy object that orbits the sun and has a long tail of gas. Some comets can be seen from Earth every few years, while others pass by once in a person's lifetime. Comets are made of ice, dust, and tiny pieces of rock, but to people on Earth, they look like streaks or smudges across the night sky.
Short-period Comets A comet with an orbital period of less than 200 years is known as a short-period comet or a âperiodic cometâ. These are now divided into Jupiter-family comets with periods less than 20 years and orbits that do not extend much beyond Jupiter, and Halley-type comets with periods of 20â200 years and highly inclined orbits.