- The Albedo of an object is the extent to which it diffusely reflects light from the sun. It is a more specific form of the term reflectivity. Albedo is defined as the ratio of diffusely reflected to incident electromagnetic radiation. It is a unitless measure indicative of a surface's or body's diffuse reflectivity. The albedo is an important concept in climatology and astronomy. In climatology it is sometimes expressed as a percentage. Its value depends on the frequency of radiation considered. In general, the albedo depends on the direction and directional distribution of incoming radiation.
- Alcubierre drive: It is a concept based on an argument that the space curvature could take the form of a wave in which a spaceship might be carried in a "bubble". Space would be collapsing at one end of the bubble and expanding at the other end. The motion of the wave would carry a spaceship from one space point to another in less time than light would take through unwarped space. Nevertheless, the spaceship would not be moving faster than light within the bubble. This concept would require the spaceship to incorporate a region of exotic matter, or "negative mass".
- Askesian Society: It is a debating club for scientific thinkers, established in 1796 in London. The name was taken from the Greek term Askesis, meaning 'training' or 'application'. It was founded by William Allen. The other two principal founders were Richard Phillips and William Haseldine Pepys, both Quakers from the Lombard Street area. The Society disbanded in 1807. Society proceedings resumed again in 2007 on the 200th anniversary of the society's 1807 dissolution. Meeting in London, young scientists and philosophers express original theory, or pay a fine of seven pounds.
- Asthenosphere: layer of soft rocks on top of which float the lithosphere.
- Intergalactic travel: It is travel between galaxies, and is considered much more technologically demanding than even interstellar travel. At the speed of light, travelling from Earth in the Milky Way galaxy to the Andromeda Galaxy (the nearest major galaxy) would take roughly two and a half million years from the perspective of observers on Earth, but would take an arbitrarily short amount of time for the traveller (due to the effects of time dilation), depending on exactly how close to the speed of light the vessel is travelling. In engineering terms, intergalactic travel is considered pure science fiction. Because of the great distances, travelling to other galaxies is definitely impractical because of the need for much more advanced propulsion methods than are currently thought possible.
- Interplanetary travel: It is travel between planets within a single planetary system. In practice, the use of the term is confined to travel between the planets of the Solar System.
- Interstellar space travel: It is unmanned or manned travel between stars. The concept of interstellar travel in starships is a staple in science fiction. Interstellar travel is tremendously more difficult than interplanetary travel due to the vastly larger distances involved, and intergalactic travel is more difficult still.
- Linnean Society of London: It is the world's premier society for the study and dissemination of taxonomy and natural history. The Linnean Society was founded in 1788, taking its name from the Swedish naturalist Carolus Linnaeus. Fellows use the designation FLS after their names.
- Lithosphere: This is the name given to the crust and part of the outer mantle of the earth.
- Lithium hydride: It is the compound of lithium and hydrogen. It is a colourless crystalline solid, although commercial samples appear gray. Characteristic of a salt-like hydride, it has a high melting point (689 °C). Its density is 780 kilograms per cubic metre. It has a standard heat capacity of 29.73 J/mol*k with thermal conductivity that varies with composition and pressure (from at least 10 to 5 W/m*K at 400 K) and decreases with temperature. It is a flammable solid and very reactive with water, producing the corrosive compound lithium hydroxide as well as hydrogen LiH + H2O ? LiOH + H2
- Royal Society of London for the Improvement of Natural Knowledge (The):
Known simply as The Royal Society, it is a learned society for science that
was founded in 1660 and claims to be the oldest such society still in existence.
Although a voluntary body, it serves as the academy of sciences of the United
Kingdom. The Royal Society is a member organization of the Science Council.
The Royal Society of Edinburgh (founded 1783) is a separate Scottish body
and the Royal Irish Academy (founded 1785) is also a separate Irish body.
- Sidereal month: The period of the Moon's orbit as defined with respect to the celestial sphere is known as a sidereal month because it is the time it takes the Moon to return to a given position among the stars: 27.321661 days (27 d 7 h 43 min 11.5 s).
- Space elevator: It is a proposed megastructure designed to transport material from a celestial body's surface into space. The term most often refers to a structure that reaches from the surface of the Earth to geosynchronous orbit (GSO) and a counter-mass beyond. Space elevators have also sometimes been referred to as beanstalks, space bridges, space lifts, space ladders, skyhooks, orbital towers, or orbital elevators.
- Synodic month: This is the average period of the Moon's revolution with respect to the sun. The synodic month is responsible for the moon phases because the Moon's appearance depends on the position of the Moon with respect to the Sun as seen from the Earth. While the moon is orbiting the earth, the Earth is progressing in its orbit around the Sun. This means that after completing a sidereal month the Moon must move a little farther to reach the new position of the Earth with respect to the Sun. This longer period is called the synodic month. Because of the perturbations of the orbits of the Earth and Moon, the actual time between lunations may range from about 29.27 to about 29.83 days.
- Warp drive: In the fictional universe of Star Trek, is a form of faster-than-light
(FTL) propulsion. It is portrayed as being capable of propelling spacecraft
or other objects to many multiples of the speed of light, while avoiding
the problems associated with time dilation. One difference between warp
drive and hyperspace is that unlike hyperspace, the ship does not enter
a different universe or a different dimension, it merely creates a small
"bubble" of normal space time. Ships in warp can interact with
objects in normal space.