An Etymological Dictionary of Astronomy and Astrophysics

Same as → red horizontal branch star.

See also: → red; → horizontal; → branch; → star.

Same as → red horizontal branch star.

See also: → red; → horizontal; → branch; → star.

The second largest satellite of Saturn, also known as Saturn V. It has a diameter of 1530 km and orbits Saturn at a mean distance of 527,040 km in 4.518 days.
Rhea is composed primarily of water ice with rock making up less than 1/3 of its mass. It was discovered by Cassini in 1672.

See also: In Gk. mythology Rhea was the sister and wife of Cronus (Saturn) and the mother of Demeter, Hades (Pluto), Hera, Hestia, Poseidon (Neptune), and Zeus (Jupiter).

The second largest satellite of Saturn, also known as Saturn V. It has a diameter of 1530 km and orbits Saturn at a mean distance of 527,040 km in 4.518 days.
Rhea is composed primarily of water ice with rock making up less than 1/3 of its mass. It was discovered by Cassini in 1672.

See also: In Gk. mythology Rhea was the sister and wife of Cronus (Saturn) and the mother of Demeter, Hades (Pluto), Hera, Hestia, Poseidon (Neptune), and Zeus (Jupiter).

A metallic chemical element; symbol Re. Atomic number 75; atomic weight 186.207; melting point about 3,180°C; boiling point about 5,625°C. Rhenium is a very dense, high-melting, silver-white metal; specific gravity
21.02 at 20°C. Of the elements, only carbon and tungsten have higher melting points and only iridium, osmium, and platinum are more dense. It was discovered by x-ray spectroscopy in 1925 by the German chemists, Walter Noddack, Ida Tacke and Otto Berg.

See also: The name derives from L. rhenus for “the Rhine river in Germany”.

A metallic chemical element; symbol Re. Atomic number 75; atomic weight 186.207; melting point about 3,180°C; boiling point about 5,625°C. Rhenium is a very dense, high-melting, silver-white metal; specific gravity
21.02 at 20°C. Of the elements, only carbon and tungsten have higher melting points and only iridium, osmium, and platinum are more dense. It was discovered by x-ray spectroscopy in 1925 by the German chemists, Walter Noddack, Ida Tacke and Otto Berg.

See also: The name derives from L. rhenus for “the Rhine river in Germany”.

A branch of physics dealing with the way matter flows and deforms.

Etymology (EN): From rheo- “flow, current, stream,” from Gk. rheos “stream,” cognate with Pers. rud “river,” → Eridanus, +
→ -logy.

Etymology (PE): Ravâné, from ravân “flowing, running,” pr.p. of raftan “to go, walk; to flow;” (Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack”) + šenâsi, → -logy.

A branch of physics dealing with the way matter flows and deforms.

Etymology (EN): From rheo- “flow, current, stream,” from Gk. rheos “stream,” cognate with Pers. rud “river,” → Eridanus, +
→ -logy.

Etymology (PE): Ravâné, from ravân “flowing, running,” pr.p. of raftan “to go, walk; to flow;” (Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack”) + šenâsi, → -logy.

Relating to a constraint or system that contains time explicitly.
For example, a pendulum with an extensible string of length l rheonomous, the condition of constraint is:

x² + y² = l²(t), where l(t) is the length of the string at time t.

See also: From Gk. rheo-, from rheos “a flowing, stream, current,” → rheology, + -nomous, → -nomy.

Relating to a constraint or system that contains time explicitly.
For example, a pendulum with an extensible string of length l rheonomous, the condition of constraint is:

x² + y² = l²(t), where l(t) is the length of the string at time t.

See also: From Gk. rheo-, from rheos “a flowing, stream, current,” → rheology, + -nomous, → -nomy.

A → yellow hypergiant in the constellation Cassiopeia, classified as F8-G2 Ia0pe. Rho Cas is about 11,650 light-years away from Earth, yet can still be seen by the naked eye, as it is 550,000 times as luminous as the Sun. It is in fact
one of the most luminous stars in our Galaxy. ρ Cas is also one of the only seven currently known yellow hypergiants in the Milky Way. It is variable and fluctuates around magnitude 5 but dimmed to 6th magnitude on 1946. Its last eruption happened in 2000-2001, during which the star ejected about 10 percent of a solar mass, dimmed by more than a full magnitude, and changed its spectral type from late F to early M. During this outburst, the star surface cooled from 7,000 to 4,000 K.

See also: Rho, a Gk. letter of alphabet used in → Bayer designation; Cassiopeiae, genitive of → Cassiopeia.

A → yellow hypergiant in the constellation Cassiopeia, classified as F8-G2 Ia0pe. Rho Cas is about 11,650 light-years away from Earth, yet can still be seen by the naked eye, as it is 550,000 times as luminous as the Sun. It is in fact
one of the most luminous stars in our Galaxy. ρ Cas is also one of the only seven currently known yellow hypergiants in the Milky Way. It is variable and fluctuates around magnitude 5 but dimmed to 6th magnitude on 1946. Its last eruption happened in 2000-2001, during which the star ejected about 10 percent of a solar mass, dimmed by more than a full magnitude, and changed its spectral type from late F to early M. During this outburst, the star surface cooled from 7,000 to 4,000 K.

See also: Rho, a Gk. letter of alphabet used in → Bayer designation; Cassiopeiae, genitive of → Cassiopeia.

A complex region of molecular and dust clouds containing emission and reflection nebulae near the star ρ Oph in the constellation → Ophiuchus. It is one of the closest star forming regions, some 400 light-years distant. Recent studies using the latest X-ray and infrared observations reveal more than 300 young stellar objects within the large central cloud. Their median age is only 300,000 years.

See also: Rho, Gk. letter; → Ophiuchus; → cloud.

A complex region of molecular and dust clouds containing emission and reflection nebulae near the star ρ Oph in the constellation → Ophiuchus. It is one of the closest star forming regions, some 400 light-years distant. Recent studies using the latest X-ray and infrared observations reveal more than 300 young stellar objects within the large central cloud. Their median age is only 300,000 years.

See also: Rho, Gk. letter; → Ophiuchus; → cloud.

A metallic chemical element; symbol Rh. Atomic number 45; atomic weight 102.9055; melting point about 1,966°C; boiling point 3,727±100°C; specific gravity 12.41 at 20°C. Rhodium was discovered in 1803 by the English chemist and physicist William Hyde Wollaston during experiments on crude platinum ore.

See also: The name derives from Gk. rhodon “rose” because of the “rose color of dilute solutions of its salts.”

A metallic chemical element; symbol Rh. Atomic number 45; atomic weight 102.9055; melting point about 1,966°C; boiling point 3,727±100°C; specific gravity 12.41 at 20°C. Rhodium was discovered in 1803 by the English chemist and physicist William Hyde Wollaston during experiments on crude platinum ore.

See also: The name derives from Gk. rhodon “rose” because of the “rose color of dilute solutions of its salts.”

Shaped like a rhombus.

See also: From rhomb, → rhombus, + → -ic.

Shaped like a rhombus.

See also: From rhomb, → rhombus, + → -ic.

A quadrilateral having all sides equal and all angles oblique.

Etymology (EN): L.L. rhombus, from Gk. rhombos “rhombus, spinning top,” from rhembesthai “to spin, whirl.”

Etymology (PE): Lowzi, resembling a lowz “almond.”

A quadrilateral having all sides equal and all angles oblique.

Etymology (EN): L.L. rhombus, from Gk. rhombos “rhombus, spinning top,” from rhembesthai “to spin, whirl.”

Etymology (PE): Lowzi, resembling a lowz “almond.”

1. An ordered recurrent alternation of strong and weak elements in the flow of sound and silence in speech; a particular example or form of rhythm.
   

2. The aspect of music comprising all the elements (as accent, meter, and tempo) that relate to forward movement.
   

3. A regularly recurrent quantitative change in a variable biological process (Merriam-Webster.com).

Etymology (EN): From L. rhythmus “movement in time,” from Gk. rhythmos “measured flow or movement, rhythm; proportion, symmetry; arrangement,” related to rhein “to flow,” from PIE root *sreu- “to flow”

Etymology (PE): Ritm, loan from Fr.

1. An ordered recurrent alternation of strong and weak elements in the flow of sound and silence in speech; a particular example or form of rhythm.
   

2. The aspect of music comprising all the elements (as accent, meter, and tempo) that relate to forward movement.
   

3. A regularly recurrent quantitative change in a variable biological process (Merriam-Webster.com).

Etymology (EN): From L. rhythmus “movement in time,” from Gk. rhythmos “measured flow or movement, rhythm; proportion, symmetry; arrangement,” related to rhein “to flow,” from PIE root *sreu- “to flow”

Etymology (PE): Ritm, loan from Fr.