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Gravity Probe B

Testing Einstein's Universe

Dictionary of Scientific Terms

A short glossary of terms used throughout the site.

[ae pEr chEr]
1. An opening through which electrons, light, radio waves, or other radiation can pass.
2. The diameter of a lens or opening in a telescope or other optical instrument, usually expressed in inches. It can also be measured as the angle between lines running from the focus object and the opposite ends of the lens's (or opening's) width.
[krai o jeh nihks]
The production and maintenance of very low temperatures, and the study of phenomena at these temperatures.
data analysis
The evaluation of data.
data reduction
1. The transformation of raw data into a more applicable form.
2. The conversion of all information in a data set into fewer dimensions for a particular purpose, as, for example, a single measure such as a reliability measure.
Dewar flask
[du Er flaesk]
A vacuum-insulated sealable container with a heat reflective inner surface. A dewar containing a cryogen (a low temperature producing substance) is known as a cryostat.
[dI dhEr]
To periodically tilt from side to side.
electromagnetic field
[ih lehk tro maeg neh tihk fild]
A region of space in which electrical and magnetic forces exist and are described by a field. It has two components, magnetic, and electric. These can be at widely varying levels relative to each other. Natural phenomena involving electomagnetic fields include light, radio waves, TV signals. The image below represents the electromagnetic field lines emanating from a rotating planet or star.
The capacity for doing work.
fused quartz
[feuzd kwawrts]
A colorless, unusually stable transparent mineral formed when crystal quartz is melted at a white heat and cooled to form an amorphous glass.
Global Positioning System (GPS)
A navigation system made up of 18 to 24 satellites, each carrying atomic clocks, to provide a receiver anywhere on earth with extremely accurate measurements of its own three-dimensional position, velocity, and time.
grand unified field theory
A theory describing the unification of gravity with the other elementary forces in physics, i.e., the weak force, the strong force and the electromagnetic force.
gravitomagnetic field
[grae vE toe maeg neh tihk fild]
In general relativity, those components of the gravitational field that are analogous to the magnetic-field components of the electromagnetic field.
gyroscope (sometimes abbreviated "gyro")
[jai rE skop]
An instrument that maintains an angular reference direction by virtue of a rapidly spinning mass. "Gyroscopes have been around since the early 1850s, when French physicist Jean-Bernard-Léon Foucault invented them to demonstrate that Earth rotated. (Foucault's more famous pendulum served the same purpose.) A gyroscope is little more than a flywheel—a bicycle wheel, for instance—that spins around an axis. But once the wheel is set spinning, the axis of the gyroscope will keep pointing in the same direction as long as no other force comes along to reorient it. This effect depends on a principle of physics known as the conservation of angular momentum, which explains why, for instance, it's easy to sit upright on a bicycle when it's rolling along and the wheels are spinning, and much, much harder to do so when it's at rest. " G. Taubs. The Gravity Probe. — Discover, Vol. 18 No. 3, March 1997, pp. 62-71.
Josephson junction
[jo sihf sEn juhngk shEn]
A device formed by two superconductors such as a thin insulating layer or point contact, which allows tunneling of Cooper pair wave functions.
Mach principle
The principle that the motion of a particle is only meaningful when referred to the rest of the matter in the universe; this motion is determined by the distribution of this matter and is not an intrinsic property of an absolute space.
A quantitative measure of a body's resistance to being accelerated; equal to the inverse ratio of the body's actual acceleration to the acceleration of a standard mass under otherwise identical conditions.
[meh tra lE ji]
The science of measurement.
[mihl le ARK sek und]
A milli-arcsecond is a thousandth part of one second of arc. A "second of arc" is a piece of an angle; it represents one sixtieth of a "minute of arc" which in turn is one sixtieth of one degree of arc. A degree is the standard unit of measurement of angles. There are 360 degrees in a circle, for example, and a "right" angle measures 90 degrees.
"Milli-arcsecond" is the industry shorthand or slang term for "one millisecond of arc."
[fo to dih tehk tEr]
A device used to detect and measure the intensity of radiant energy through photoelectric action.
1. An instrumented vehicle that is located in the upper atmosphere, space or upon another celestial body and used to obtain information about the specific enviroment.
2. The vacuum tube which houses the science instrument assembly, the electrical cables and connectors which connect the gyro susupension, SQUIDs, telescope detectors, and SIA instrumentation to their electronics boxes. The probe is installed in the Dewar well.
[kwan tEm]
1. Any of the very small increments or parcels into which many forms of energy are subdivided.
2. Any of the small subdivisions of a quantized physical magnitude (as magnetic moment).
quantum detector
A device that detects electromagnetic radiation by converting a quantum of the radiation into a proportionate signal, while remaining insensitive to quanta of less than a certain energy. Examples include photographic emulsions, photoelectric cells, and Geiger counters.
[ro tEr]
The rotation member of an electrical machine or device, such as the rotating armature of a motor or generator, or the rotating plates of a variable capacitor.
A four-dimensional space used to represent the universe in the theory of relativity, with three dimensions corresponding to ordinary space and the fourth to time. Also known as space-time continuum. See more about this in the FAQ section.
Devices, either manned or unmanned, which are designed to be placed into an orbit about the earth or into a trajectory to another celestial body. Also known as a space ship; space vehicle.
[su pEr kan dEk tI vih ti]
A property of many metals, alloys, and chemical compounds at temperatures near absolute zero, by which their electrical resistivity vanishes and magnetic fields are expelled.
[su pEr kEn duhk tEr]
Any material capable of exhibiting superconducting properties. Examples include iridium, lead, mercury, niobium, tin, tantalum, vanadium, and many alloys. Also known as a cryogenic conductor.
Superconducting Quantum Interference Device (SQUID)
A sensor composed of a superconducting ring coupled with one or two Josephson junctions; applications include high-sensitivity magnetometers, near-magnetic-field antennas, and measurement of very small currents or voltages.
superfluid helium
[su pEr flu id hi li Em]
Liquid helium kept at temperatures near absolute zero and capable of flowing completely without friction through holes as small as 10-7 centimeters in diameter, with partical velocities less than a few centimeters per second.
Transmitting instrument readings to remote locations through wires, radio waves, or other means. Also known as remote metering.
The dividing line between the bright and shaded regions of the disk of the moon or an inner planet.