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- Laboratory
- the location where a scientist conducts research. It is often, but not always, a room with specialized equipment and safety precautions. Often abbreviated as “lab.”
- Laser Inertial Fusion energy (LIFE)
- a fusion energy concept for delivering energy to the electrical grid.
- Law of Reflection
- the angle of incidence equals the angle of reflection.
- Law of Refraction
- As a light ray passes from one medium to another (i.e. water to glass), it will bend. The amount of bending depends on how much light is slowed down by the material.
- Lenticular Galaxy
- these galaxies are flattened disks like the spiral galaxy. They do not, however, have the spiraling arms, and have much lower rates of new star formation. Similar to ellipticals, lenticular galaxies have little or no cool gas or dust.
- Lepton
- one of the 3 most fundamental building blocks of the Universe, along with quarks and bosons. The most common lepton is the electron.
- Life Cycle of Stars
- the cycle in which stars are born as protostars, grow old by expending their nuclear fuel, and eventually end their lives as black holes, white dwarfs and neutron stars. Stars expel material that will eventually form new stars; sometimes slowly over the long course of their lives, and sometimes quickly and violently in the form of supernovas.
- Light Curve
- a graphical depiction of the brightness of an object as a function of time.
- Light Side
- the part of the Moon the sun is currently shining on. The side of the Moon that receives sunlight changes as the Moon orbits around the earth.
- Light-week
- the distance light travels in a week; approximately 181 billion kilometers (1.8 x 1011 kilometers) or 1.8 x 1014 m.
- Light-year
- the distance light travels in one year; approximately 9.5 trillion (9.5 x 1012) kilometers. Since light travels so fast, it covers a lot of distance in a small amount of time and because the universe is so large it makes it easy for astronomers to use light-years as a measuring stick.
- Long Gamma-Ray Burst
- A gamma-ray burst lasting more than two seconds to several minutes which is often associated with a core-collapse supernova and the subsequent birth of a neutron star or black hole.
- Loop
- a block of computer code that can repeat for a fixed number of times, or until some condition is met, or forever.
- Luminosity
- the measured energy emitted each second by a celestial body. This includes all wavelengths of light. Note that this is not necessarily the same as the apparent brightness because two objects with the same luminosity can appear different brightness if they are at different distances. The SI unit for luminosity is watts: the luminosity of the Sun is approximately 4 x 1026 W.
