An Etymological Dictionary of Astronomy and Astrophysics
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The → radiation pressure of solar photons, which pushes a comet's dust outward to form a → dust tail.

→ solar; → radiation; → pressure.

Plural form of → solar radius.

→ solar; → radii.

A unit of length, representing the radius of the → Sun, used to express the size of stars in astrophysics. It is equivalent to: 695,700 km, 0.00465047 → astronomical units, 7.35355 × 10^-8 → light-years, and 2.32061 → light-seconds.

→ solar; → radius.

The motion of the Sun around an axis which is roughly perpendicular to the plane of the → ecliptic; the Sun's rotational axis is tilted by 7.25° from perpendicular to the ecliptic. It rotates in the → counterclockwise direction (when viewed from the north), the same direction that the planets rotate (and orbit around the Sun). The Sun's rotation is differential, i.e. the period varies with latitude on the Sun (→ differential rotation). Equatorial regions rotate in about 25.6 days. The regions at 60 degrees latitude rotate more slowly, in about 30.9 days.

→ solar; → rotation.

A space vehicle designed to orbit about the Sun.

→ solar; → satellite.

The spectrum of the Sun's electromagnetic radiation, consisting of a continuum spectrum marked with dark absorption lines.

→ solar; → spectrum.

The collective name for the Sun and all objects gravitationally bound to it. These objects are the eight planets, their 166 known moons, five dwarf planets, and billions of small bodies. The small bodies include asteroids, icy Kuiper belt objects, comets, meteoroids, and interplanetary dust. The solar system is roughly a sphere with a radius greater than 100,000 AU. Planets, satellites, and all interplanetary material together comprise only about 1/750 of the total mass. Geochemical dating methods show that the solar system chemically isolated itself from the rest of the Galaxy (4.7 ± 0.1) × 10⁹ years ago.

→ solar; → system.

Same as → protosolar abundance.

→ solar system; → abundance.

A telescope designed so that heating effects produced by the Sun do not distort the images.

→ solar; → telescope.

The time based on the rotation of the Earth relative to the Sun. → mean solar time.

→ solar; → time.

A structure used in solar observations in order to raise the equipment above the atmospheric disturbances caused by solar heating of the ground and the radiation of the heat into the atmosphere.

→ solar; → tower.

An ideal star possessing fundamental physical parameters (mass, chemical composition, age, effective temperature, luminosity, gravity, magnetic fields, equatorial rotation, etc.) very similar, if not identical, to those of the Sun. See also → solar analog; → solar-like star.

→ solar; → twins paradox.

The rate of change of the Sun's position with respect to the local standard of rest toward the → solar apex.

→ solar; → velocity.

A mass outflow, consisting of protons, electrons, and other subatomic particles, expelled constantly from the solar corona at about 500 km per second. The solar mass-loss rate in this phenomenon amounts to about 2 x 10^-14 solar masses per year, or about 10⁶ tons per second. → stellar wind.

→ solar; → wind.

The period of time required for the Earth to make one complete revolution around the Sun. Solar year is a general term for: → tropical year, → vernal equinox year, and → autumnal equinox year, which have different lengths.

→ solar; → year.

A member of a very broad class of stars in which is found a mixture of late F, early, middle, and, sometimes, late G type dwarfs and sub-giants. See also → solar analog; → solar twin.

→ solar; → -like; → star.

Any of the various phenomena observable on the Earth that are caused by the influence of the Sun, such as aurora borealis.

→ solar; → terrestrial; → phenomenon.

A criterion for → convective stability in → massive stars. The Solberg-Høiland stability criterion corresponds to the inclusion of the effect of → rotation (variation of → centrifugal force) in the convective stability criterion. It is a combination of → Ledoux's criterion (or possibly → Schwarzschild's criterion) and → Rayleigh's criterion. Both the dynamical shear and Solberg-Høiland instabilities occur in the case of a very large → angular velocity decrease outwards. Therefore, in a → rotating star the Ledoux or Schwarzschild criteria for convective instability should be replaced by the Solberg-Høiland criterion. More specifically, this criterion accounts for the difference of the centrifugal force for an adiabatically displaced fluid element. It is also known as the axisymmetric baroclinic instability. It arises when the net force (gravity + buoyancy + centrifugal force) applied to a fluid parcel in an adiabatical displacement has components only in the direction of the displacement (A. Maeder, Physics, Formation and Evolution of Rotating Stars, 2009, Springer).

E. Høiland, 1939, On the Interpretation and Application of the Circulation Theorems of V. Bjerknes. Archiv for mathematik og naturvidenskab. B. XLII. Nr. 5. Oslo.
H. Solberg, 1936 (reprint), Le mouvement d'inertie de l'atmosphere stable et son rôle dans la théorie des cyclones.
H. Solberg, 1941, On the Stability of the Circular Vortex. Avhandl. utg. av Det Norske Videnskaps-Akademi i Oslo. I. Mat-Naturv. Klasse. No. 11.
Wasiutynski, J. 1946, Astrophysica Norvegica, 4, 1.

The bottom or under surface of the → foot.

M.E., from O.Fr., from L. solea "sandal, bottom of a shoe," from solum "base, bottom, ground," of unknown origin.

From kaf, "the sole of the foot; the palm of the hand," → floor; pâ, → foot.

An optical compensator which produces a constant phase change over the entire field, as opposed to the phase change produced by the → Babinet compensator, which occurs progressively across the field. The compensator consists of two wedges of the same wedge angle and a parallel plate. The optic axes of the two wedges has the same orientation. These form a variable thickness plate. One of the wedges is assembled to the fixed parallel plate. The optic axis of the parallel plate is at 90° to that of the wedges. The other wedge is attached to a micrometer and moves to produce a thickness difference between the fixed and variable thickness plates, thus producing a phase delay.

Jean-Baptiste Soleil (1798-1849); → compensateur.