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The Swiftest Planet
Sun-scorched Mercury is only slightly larger than Earth's moon. Like the moon, Mercury has very little atmosphere to stop impacts, and it is covered with craters. Mercury's dayside is super-heated by the sun, but at night temperatures drop hundreds of degrees below freezing. Ice may even exist in craters. Mercury's egg-shaped orbit takes it around the sun every 88 days.

 News Features People Extreme Facts Dictionary

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 labes A landslide.
 labyrinthus An intersecting valley complex.
 lacus A lake.
 Lagrange points Lagrange showed that three bodies can lie at the apexes of an equilateral triangle which rotates in its plane. If one of the bodies is sufficiently massive compared with the other two, then the triangular configuration is apparently stable. Bodies at such points are sometimes referred to as Trojans. The leading apex of the triangle is known as the leading Lagrange point or L4; the trailing apex is the trailing Lagrange point or L5. Collinear with the two large bodies are the L1, L2 and L3 unstable equilibrium points which can sometimes be useful places for spacecraft, eg SOHO. (For a more detailed explanation, click on the diagram to the right).
 latitude The angular distance north or south from the equator.
 leading hemisphere The hemisphere that faces forward, into the direction of motion of a satellite that keeps the same face toward the planet.
 lidar An instrument similar to radar that operates at visible wavelengths.
 light pollution The illumination of the night sky by waste light from cities and outdoor lighting, which prevents the observation of faint objects. This is why it is hard to see stars in big cities.
 light-year The distance light travels in one year. 1 ly = 9.46*10^15 meter = 5.9 billion miles.
 limb The outer edge of the apparent disk of a celestial body.
 linea Elongate marking.
 liquid crystal A substance that behaves like both a liquid and a solid.
 liter = 1000 cm3 = 1.06 US quarts.
 longitude The angular distance east or west from the prime meridian.
 lunar Relating to the moon.
 lunar month The average time between successive new or full moons, equal to 29 days 12 hours 44 minutes. Also called synodic month.

Can't find it? Don't understand it? Ask us.
 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
 Find entries starting with containing
 labes A landslide.
 labyrinthus An intersecting valley complex.
 lacus A lake.
 Lagrange points Lagrange showed that three bodies can lie at the apexes of an equilateral triangle which rotates in its plane. If one of the bodies is sufficiently massive compared with the other two, then the triangular configuration is apparently stable. Bodies at such points are sometimes referred to as Trojans. The leading apex of the triangle is known as the leading Lagrange point or L4; the trailing apex is the trailing Lagrange point or L5. Collinear with the two large bodies are the L1, L2 and L3 unstable equilibrium points which can sometimes be useful places for spacecraft, eg SOHO. (For a more detailed explanation, click on the diagram to the right).
 latitude The angular distance north or south from the equator.
 leading hemisphere The hemisphere that faces forward, into the direction of motion of a satellite that keeps the same face toward the planet.
 lidar An instrument similar to radar that operates at visible wavelengths.
 light pollution The illumination of the night sky by waste light from cities and outdoor lighting, which prevents the observation of faint objects. This is why it is hard to see stars in big cities.
 light-year The distance light travels in one year. 1 ly = 9.46*10^15 meter = 5.9 billion miles.
 limb The outer edge of the apparent disk of a celestial body.
 linea Elongate marking.
 liquid crystal A substance that behaves like both a liquid and a solid.
 liter = 1000 cm3 = 1.06 US quarts.
 longitude The angular distance east or west from the prime meridian.
 lunar Relating to the moon.
 lunar month The average time between successive new or full moons, equal to 29 days 12 hours 44 minutes. Also called synodic month.