|
|
In a system of two large bodies (Sun-Earth or Earth-Moon), these are the points where a small third body will keep a fixed position relative to the other two. Named for French astronomer Louis Lagrange (1736-1813) who first studied them and who showed there existed 5 such points. In the Sun-Earth system only two are important, both on the Earth-Sun line--the L1 point 236 Earth radii sunward of Earth, and the L2 point at a similar distance on the night side. The L1 point is a good "early warning" outpost intercepting shocks and particles emitted by the Sun and its vicinity has been occupied by several spacecraft. Altogether five Lagrangian points exist in the Earth-Sun or Earth-Moon system.
|
|
Two angles which specify a location on Earth. If a line is drawn from the Earth's center to the given location, then latitude is the angle between that line and its projection on the plane of the Earth's equator (latitude also equals 90o- q, where the "co-latitude" q is the angle between the line and the axis of the Earth).
To define longitude, imagine a large number of planes ("meridional planes") all of which contain the axis of the Earth. Assuming the equator is a circle, divide it into 360 degrees and fractions of degrees: then each meridional plane can be labeled by the angle at its intersection of the equator, and the longitude of a point is the angle f marking the meridional plane on which it sits. Longitude is similar to the angle f of 3-dimensional polar coordinates or to right ascension, but is measured from a zero longitude chosen as the longitude of the Greenwich observatory near London, Great Britain.
|
|
Another name for Kepler's 2nd law.
|
|
A periodic back-and-forthswing of the elongated axis of the Moon, across the Moon-Earth line. It resembles the swings of two-pan scales (in Latin, "Libra") around their points of equilibrium. Because of libration, the Moon shows Earth (now and then) areas beyond the 50% of the surface facing Earth.
|
|
the lifting force on a flying object (in particular, a wing or an aircraft), due to its motion relative to the surrounding air. Lift is one of the four forces sensed by an airplane, the others being drag, thrust and weight.
|
|
A sudden electric flow between a thunderstorm cloud and the ground (or another cloud), for a brief instant producing heat and light along its path (and the heat, in turn, producing a sudden expansion of air, which initiates the thunder). Lightning removes electric charge, created in collisions of freezing raindrops. Large drops fall down, while small ones, carrying charges of the opposite sign, rise up because the force of gravity pulling them down is overcome by upward-blowing winds. The work performed by separating opposite charge ends up as electric energy, at high voltages.
|
|
Rockets in which a liquid fuel (kerosene, liquid hydrogen) is combined in a combustion chamber with a liquid oxidizer (usually liquid oxygen, also fuming nitric acid or hydrogen peroxide). Very efficient and controllable, such rockets are generally used in spaceflight. Unlike solid fueled rockets, they can be shut off by remote command, simply by closing off their fuel line.
|
|