An Etymological Dictionary of Astronomy and Astrophysics
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A → binary system composed of two → neutron stars.

→ neutron; → star; → binary; → system.

A → multiple star system that lacks the characteristics of a → hierarchical multiple system.

→ non-; → hierarchical; → multiple; → system.

A mechanical system with constraints on their velocity that are not derivable from position constraints. Nonholonomic systems arise, for instance, in mechanical systems that have rolling contact (for example, the rolling of wheels without slipping) or certain kinds of sliding contact (such as the sliding of skates). They are a remarkable generalization of classical Lagrangian and Hamiltonian systems in which one allows position constraints only.

→ non-; → holonomic; → system.

A system in which small changes can result in large effects, and large changes in small effects.

→ nonlinear; → system.

Same as → numeral system.

→ number; → system.

The conversion of a → number system with a given → base to another system with a different base; such as the conversion of a → decimal number (base 10) to a → binary number system (base 2). In order to convert a number into its representation in a different number base, we have to express the number in terms of powers of the other base. For example, to convert the decimal number 100 to base 3, we must figure out how to express 100 as the sum of powers of 3. We proceed as follows:
1: Divide the decimal number to be converted (100) by the value of the new base (3).
2: Get the remainder from Step 1 (that is 1) as the rightmost digit (least significant digit) of new base number.
3: Divide the quotient of the previous divide (33) by the new base.
4: Record the remainder from Step 3 (0) as the next digit (to the left) of the new base number.
Repeat Steps 3 and 4, getting remainders from right to left, until the quotient becomes zero in Step 3 (2 and 0).
The last remainder thus obtained (1) will be the most significant digit of the new base number.
Therefore, 100₁₀ = 10201₃.
Conversely, to convert from another base to decimal we must:
1: Determine the column (positional) value of each digit.
2: Multiply the obtained column values (in Step 1) by the digits in the corresponding columns.
3: Sum the products calculated in Step 2. The total is the equivalent value in decimal.
For example, the binary number 1100100 is determined by computing the place value of each of the digits of the number:
(1 × 2⁶) + (1 × 2⁵) + (0 × 2⁴) + (0 × 2³) + (1 × 2²) + (0 × 2¹) + (0 × 2⁰) = 64 + 32 + 0 + 0 + 4 + 0 + 0 = 100.

→ number; → system; → conversion.

A set of → symbols and → rules for representing → numbers. Same as → number system. See also: → Greek numeral system, → Roman numeral system, → Indian numeral system.

→ numeral; → system.

An → optical system in which the → optical axis of the → aperture is not coincident with the mechanical center of the aperture.

→ off; → axis; → optical; → system.

Thermodynamics: A system which can exchange both energy and matter with the surroundings. → closed system; → isolated system.

→ open; → system.

The program that, after being initially loaded into the → computer by a boot program, → manages all the other → programs in a computer.

→ operating; → system.

A collection of lens, prisms, mirrors, and/or other devices, placed in some specified configuration, to act on light (reflect, refract, disperse, polarize, etc.) and perform some definite optical function.

→ optical; → system.

A → crystal system that has three mutually perpendicular axes, each of which is of a different length than the others.

→ orthorhombic; → crystal; → system.

An electronic system which emits no energy, and is not detectable.

→ passive; → system.

Arrangement of the → chemical elements in the → periodic table.

→ periodic; → system.

A system of → magnitudes, each of them characterized by a set of well-defined → passbands (or → filters) with known → response curves. The system is defined by the values given for the → standard stars. See also:
→ AB magnitude system, → five-color system, → Stromgren system, → JHK system, → UBV system, → uvby system.

→ photometric; → system.

A set of physical components chosen to study their relations.

→ physical; → system.

→ Interplanetary dust and other small particles organized into thin, flat rings encircling a planet. The most spectacular planetary rings known are those around → Saturn, but the other three → giant planets of the solar system (→ Jupiter, → Uranus, and → Neptune) have their own ring systems.

→ planetary; → ring; → system.

A system composed of a star and all the celestial bodies bound to it by gravity, especially planets and their natural satellites.

→ planetary; → system.

A → number system in which the value of each digit is determined by which place it appears in the full number. The lowest place value is the rightmost position, and each successive position to the left has a higher place value. In the → number system conversion, the rightmost position represents the "ones" column, the next position represents the "tens" column, the next position represents "hundreds", etc. The values of each position correspond to powers of the → base of the number system. For example, in the usual decimal number system, which uses base 10, the place values correspond to powers of 10. Same as → place-value notation and → positional notation. See also → number system conversion.

→ positional; → number; → system.

An empirical model developed by Ptolemy about 150 A.D., in which a motionless Earth was the center of the Universe. The Sun, Moon, and planets revolved around the Earth in → eccentric circles and → epicycles. The fixed stars were attached to an outer sphere concentric with Earth. The Ptolemaic system gave the positions of the planets accurately enough for naked-eye observations, although it also had serious defects. As an extreme example, according to Ptolemy's model for the Moon, our satellite should appear to be almost twice as large when it is full than it is at quadrature, which is an absurdity since it is not seen as such.

Claudius Ptolemaeus was a mathematician, geographer, astronomer, and astrologer. The most influential of Greek astronomers, he lived in Roman Egypt, and was probably born there; he died in Alexandria in 165 A.D.; → system.