Astro Glossary

Little Dipper

Like its larger counterpart, the Big Dipper, the Little Dipper is an “asterism” — a group of stars that forms an easy-to-see pattern but that is not a full constellation. It resembles a ladle or cart, with the tip of its handle marked by Polaris, the North Star. It is part of the constellation Ursa Minor, the little bear.

Local Group

Our galactic neighborhood, including the Milky Way, Andromeda Galaxy, M33, and more than 30 smaller galaxies. The Local Group appears to be a suburb of a supercluster of galaxies that lies 60 million light-years away, known as the Virgo Supercluster.

Lucy mission

Lucy is a spacecraft designed to study Jupiter's Trojan asteroids. These chunks of ice and rock share the orbit of Jupiter, but they aren't near the giant planet. One clump is 60 degrees ahead of Jupiter, the other 60 degrees behind. They ae held in place by the gravity of Jupiter and the Sun. Astronomers have cataloged more than 5,000 of them, although there could be millions. Trojans probably are “leftovers” from the birth of the solar system. They contain the same materials that were incorporated into the planets, so studying them should tell scientists more about how the planets formed. Launched October 21, 2021, Lucy is scheduled to fly past one asteroid in the asteroid belt, between the orbits of Mars and Jupiter. It will reach one group of Trojans in 2027, and eventually swing by five of its members. It then will skip past Earth, using our planet’s gravity to reach the other clump in 2033.

Lunar Crater Observation and Sensing Satellite (LCROSS)

A satellite that slammed into a crater at the Moon’s south pole in 2009. The impact scattered debris high above the lunar surface. Another lunar craft and telescopes on Earth observed the impact and discovered that the material it excavated included water, confirming earlier observations that shaded craters at the poles could contain large amounts of water ice.

Lunar Craters

Lunar Exploration

Lunar Folklore

Lunar Orbiter Project

NASA launched five Lunar Orbiter missions from 1965 to 1967. Each was designed to image a large portion of the lunar surface to help Apollo mission planners select good landing sites for astronauts. Each orbiter shot its images on film, developed the film, scanned the images, and transmitted them to Earth in strips. The technology was based in part on that developed for Earth-orbiting spy satellites. All five Lunar Orbiter missions were successful. Scientists combined their images to produce the best maps of the Moon to that time, and the images continue to provide an important resource for lunar scientists.

Lunar Phases

The apparent shapes of the Moon as seen from the Earth, which are caused by the Moon’s orbit of the Earth once every 29.5 days. The same phase will fall on the same date of the year according to the Saros cycle, every 18 years, 11 days, and eight hours. See our moon phases page for more information.

Lunar Prospector

Lunar Prospector was one of the NASA Discovery Program missions, which emphasized “Faster, Better, Cheaper” mission design and development. Lunar Prospector was designed to perform a low polar orbit investigation of the Moon, which included mapping the surface composition and locating lunar resources, measuring magnetic and gravity fields, and studying outgassing events.