An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Any change in the phase of a periodic quantity or in the phase difference between two or more periodic quantities.

→ phase; → shift.

Of a dynamical system, a six-dimensional space consisting of the set of values that the position and velocity can take together (x, y, z, v_x, v_y, v_z). → velocity space.

→ phase; → space.

A measure of the relative phase in the image as function of frequency. It is the phase component of the → optical transfer function. A relative phase change of 180°, for example, results in an image with the black and white areas reversed.

→ phase; → transfer; → function.

The changing of a substance from one phase to another, by → freezing, → melting, → boiling, → condensation, or → sublimation. Also known as phase transformation. A well known phase transition is the transition from → water to → ice. Phase transitions are often associated with → symmetry breaking. In water there is a complete symmetry under rotations with no preferred direction. Ice has a crystal structure, in which certain orientations in space are preferred. Therefore, in transition from water to ice the continuous rotational symmetry is lost.

→ phase; → transition.

The speed at which any fixed phase (individual wave) in a → wave packet travels. It is expressed as v_ph = ω/k, where ω is the → angular frequency and k the → wave number. See also the → group velocity.

→ phase; → velocity.

→ Lunar phase.

→ phase; → Moon.

The gradual variation of the apparent shape of → Venus between a small, full → disk and a larger → crescent. The first telescopic observation of the phases of Venus by Galileo (1610) proved the → Ptolemaic system could not be correct. The reason is that with the → geocentric system the phases of Venus would be impossible. More specifically, in that model Venus lies always between Earth and Sun. Hence its fully bright surface would always be toward the Sun; so Venus could not be seen in full phase from Earth. Only slim crescents would be possible. On the other hand, this phenomenon could not prove the → heliocentric system, because it could equally be explained with the → Tychonic model.

→ phase; → Venus.

The study of the biological recurring phenomena in plants and animals (such as blossoming, hibernation, reproduction, and migration) and of their relation to changes in season and climate.

From L. phaeno-, from Gk. phaino-, from phainein "bring to light, cause to appear, show," from PIE root *bha- "to shine" + → -logy.

Zistcarxe-šenâsi, literally study of "life cycle," from zistcarxe "life cycle," from zist, → bio-, + carxe, → cycle, + -šenâsi, → -logy.

1) An occurrence, circumstance, or fact, in matter or spirit, which can be perceived by human senses. → physical phenomenon.
2) Philosophy: For Kant, a thing as it is apprehended by the human senses as distinguished from a noumenon, or thing-in-itself.

From L.L. phænomenon, from Gk. phainomenon "that which appears or is seen," from phainesthai "to appear," passive of phainein "to bring to light; to show," from PIE base *bhhā- "to shine;" cf. Skt. bhāati "shines, glitters;" Av. bā- "to shine, appear, seem," bāmya- "light, luminous, bright," bānu- "light, ray;" Mid.Pers. bâm "beam of light, splendor," bâmik "brilliant," bâmdâd "morning, dawn."

Padidé, noun from padid "manifest, evident, conspicuous, in sight," variant padidâr, from Mid.Pers. pad didâr "visible," from pad "to, at, for, in," evolved to bé "to; for; in; on; with; by" in Mod.Pers. (O.Pers. paity; Av. paiti "to, toward, in, at;" cf. Skt. práti, Gk. poti) + did past stem of didan "to see, regard, catch sight of, contemplate, experience" (O.Pers. dī- "to see;" Av. dā(y)- "to see," didāti "sees;" cf. Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen").

A blue → giant star in the constellation → Ursa Minor, also known as HR 5735, HD 137422, HIP 75097, BD+72°79, and SAO 8220. It has an → apparent visual magnitude of +3.0, → color indices of B -V = +0.09, U - B = +0.08, and a → spectral type of A2 III. Pherkad has a → luminosity of 1,100 Lsun, a radius of 15 Rsun, and a → surface temperature of 8,200 K. It lies 487 → light-years away from Earth.

From Ar. Al-Farqad (الفرقد) "calf."

A correlation between the peak brightness of → Type Ia supernovae and the decline rate of their → light curve (15 days after the maximum). The decline rate is also correlated to the width of the peak brightness of the supernova. The brightest events are the broadest in time and brighter SNe Ia decline more slowly than dimmer ones. Applying the Phillips relation reduces the dispersion in the light curves of Type Ia SNe thus making them precise distance indicators which can be observed over large distances.

Named after Mark M. Phillips (1951-), American astronomer (Phillips et al. 1993, ApJ 413, L105); → relation.

A person who engages in → philosophy.

M.E., from O.E. philosophe, from L. philosophus "philosopher," from Gk. philosophos "philosopher, sage," literally "lover of wisdom," → philosophy; the agent noun ending -er appears in early 14th century from an Anglo-French or O.Fr. variant of philosophe.

Filsuf, from Ar., from Gk., as above. Falsafedân, literally "philosophy knower," with -dân present stem of dânestan "to know," → science.

To explain or argue in terms of philosophical speculations or theories.

→ philosophy; → -ize.

A conceptual study that attempts to understand reality and answer fundamental questions about knowledge, existence, life, morality, and human nature. Philosophy deals with issues that generally are not subject to investigation through experimental verification. It focuses on questions which cannot be answered by means of observation alone. See also → philosophy of science.

From O.Fr. filosofie "philosophy, knowledge," from L. philosophia, from Gk. philosophia "love of wisdom," from philo- "loving" combining form of philos "dear; friend," from philein  "to love," of unknown origin, +  sophia "knowledge, wisdom," from sophis "wise, learned;" of unknown origin.

Falsafé, from Ar. falsafah, loan from Gk. philosophia, as above.

The critical study of the basic principles and concepts of a particular branch of  knowledge. The philosophy of science is particularly concerned with the nature of scientific facts, the structure of scientific statements, and relations between them.

→ philosophy; → science.

A hypothetical substance that, prior to the discovery of → oxygen, was thought to be released during → combustion. → phlogiston theory.

From New Latin, from Gk. phlogiston, neuter of phlogistos "inflammable, burnt up," from phlogizein "to set on fire, burn," from phlox "flame, blaze;" from PIE root *bhel- "to shine, burn."

Fložiston, loan from Fr, as above.

An obsolete theory of combustion in which all flammable objects were supposed to contain a substance called → phlogiston, which was released when the object burned. The existence of this hypothetical substance was proposed in 1669 by Johann Becher, who called it terra pinguis "fat earth." For example, as wood burns it releases phlogiston into the air, leaving ash behind. Ash was therefore wood minus phlogiston. In the early 18th century Georg Stahl renamed the substance phlogiston. The theory was disproved by Antoine Lavoisier in 1783, who proved the principle of conservation of mass, refuted the phlogiston theory and proposed the oxygen theory of burning.

→ phlogiston; → theory.

The inner → satellite of → Mars orbiting less than 6,000 km above the surface of Mars, closer to its → primary than any other → moon in the → solar system. Phobos is irregularly shaped, 27 x 22 x 18 km in size and orbits Mars in 0.319 days. Phobos' orbit is decaying at a rate of about 2 centimeters per year; it is therefore expected to break up and crash onto Mars within the next 50 million years. See also: → Roche limit, → orbit decay.

In Gk. mythology, Phobos is one of the sons of Ares (Mars) and Aphrodite (Venus). The name means "fear, panic, flight."

The outermost of Saturn's known satellites, also known as Saturn IX. It is 220 km in diameter and orbits Saturn in 550.5 days at a distance of 12,952,000 km.

In Gk. mythology, Phoebe is the daughter of Uranus and Gaia; grandmother of Apollo and Artemis.

A giant ring around Saturn spanning an area of space from a distance of ~ 128 Saturn equatorial radii, R_S (60,330 km) to 207 R_S, that is, from about 7.7 × 10⁶ to 12.4 × 10⁶ km from the planet. Its vertical thickness is about 40 R_S. The Phoebe ring was detected in 2009 using NASA's infrared → Spitzer Space Telescope. The Phoebe ring is made up mainly of dust particles about 10 to 20 microns in size, or about one-tenth to one-fifth the average width of a human hair. Rocks that are the size of soccer balls or larger with diameters of more than about 20 cm make up no more than about 10 percent of the ring (Verbiscer et al., 2009, Nature, 461, 1098).

→ Phoebe; → ring.