ASTR 103 - Astronomy

Glossary - S

saros

Period of 18 years and 11 days in which eclipses repeat themselves.

satellite

 

Schwarzschild radius

Critical radius of the event horizon reached by a gravitationally collapsing body between the point of visibility as a highly compressed body and nonvisibility as a black hole.

scattering

 

scintillation

Twinkling effect observed when light from a very small radiating source passes through a turbulent medium.

sedimentary rocks

 

seeing

The astronomical term used to denote our atmosphere's influence on image quality.

seismic

Pertaining to earthquakes.

semimajor axis (of an ellipse)

 

Seyfert galaxy

class of spiral galaxy that exhibits intense, irregular, electromagnetic radiations within a small active nucleus.

shock wave

conical pattern in space produced when an object moves at supersonic speed in a gaseous medium and creates a disturbed wake.

short-period comet

comet that orbits the Sun in a period less than about 200 years.

sidereal day

 

sidereal month

 

sidereal period

one complete revolution of a celestial body with respect to a fixed point in the heavens, such as a star.

sidereal time

 

sidereal year

 

signs of the zodiac

twelve equally spaced constellation divisions centered on the ecliptic, through which the Sun passes monthly in succession.

silicates

mineral compositions largely containing silicon and oxygen.

solar activity

 

solar constant

rare at which solar radiation is received on a unit surface perpendicular to the incident radiation per unit of time at Earth's mean distance, just outside Earth's atmosphere.

solar luminosity (L.)

 

solar masses (M.)

 

solar nebula

fragmented portion of an interstellar cloud that has begun to contract under its own gravitation, eventually leading to the formation of a planetary system.

solar radii (R.)

 

Solar System

 

solar wind

continuous stream of charged particles (mostly protons and electrons) ejected radially from the Sun at high velocities.

solid

that state of matter in which the constituent

particles maintain a permanent relation to each other.

solstice

 

space-time

four-dimensional world of space and time as visualized in the theory of relativity. An event is located in the space-time continuum analogous to a point in three-dimensional space.

space velocity

true motion of the star in space relative to the Sun.

special relativity

part of Einstein's theory relating to observers moving uniformly with respect to each other.

speckle photography

technique of taking very short exposures of a star, which freezes the image in a set position on each photograph, and computer-analyzing the many photographs to obtain the star's unsmeared, better-resolved image.

spectral class

 

spectral type

 

spectrogram

photographic plate on which the spectrum of an object is recorded by the telescope.

spectrograph

basically the same as the spectroscope except that the eyepiece is replaced by a photographic plate for recording the spectrum.

spectroheliogram

photograph of the Sun taken with a spectroheliograph.

spectroheliograph

spectrograph modified to photograph the solar disk or the chromosphere in the light of a single spectral line, either in the red hydrogen alpha line or the violet H or K line of calcium.

spectroscope

optical instrument containing a prism or grating with appropriate lenses to permit direct viewing of the spectrum of a radiating source.

spectroscopic binary

double star whose components are not observed separately in a telescope but whose binary character is revealed by the periodic Doppler shift of spectral lines.

spectroscopic parallax

derivation of the star's distance (or parallax) from its apparent magnitude and its absolute magnitude on the basis of its luminosity and spectral characteristics.

spectroscopy

that branch of physics and astronomy dealing with the color or wavelength composition of composite or white light.

spectrum

spreading out of the energy of a radiating source into its component wavelengths by means of a prism, grating, or other dispersing device.

spectrum-luminosity diagram

Hertzsprung-Russell diagram that exhibits the relationship between the absolute magnitudes of stars and their spectral classes.

speed

 

spherical aberration

failure of light rays striking all parts of a lens or a mirror with a spherical surface to converge at the same focal setting.

spicule

small spikeline protrusion arising within the chromosphere.

spiral arms

 

spiral galaxy (normal)

large system of stars and interstellar matter having the shape of a flattened disk with outlying spiral arms.

s process

 

standard time

 

star

 

state of motion

the motion of a body is some frame of reference as denoted by its velocity.

static cosmological model

 

steady-state cosmology

model in which it is assumed that the density of matter within the Universe remains constant as the Universe expands.

Stefan-Boltzmann law

Formula that relates the emission (E) of electromagnetic radiation by a blackbody to the fourth power of its temperature (T), E oc T⁴.

stellar association

spare aggregation of young population I stars having a common origin and found in the outer gas-dust regions of the Galaxy.

stellar cluster

 

stellar evolution

 

stellar model

 

stratosphere

narrow atmospheric zone that lies above the lowest level of Earth's atmosphere, the troposphere. It extends from about 11 to 25 kilometers above sea level and has a constant temperature of -55oC.

strong nuclear force

nuclear "glue" or binding force that holds the nucleons together against the disruptive repulsive force of the positively charged protons. It operates within the nuclear domain (-10-13 centimeter).

subatomic particle

the constituent parts of the atom, such as the electron, proton, neutron, etc.

subduction zone

 

subdwarf star

 

subgiant star

 

summer solstice

 

Sun

 

sunspot

Dark marking visible on the Sun's surface. Although the sunspot temperature is about 4500 K, it appears dark by comparison with the brighter and hotter photospheric background.

sunspot cycle

 

sunspot group

 

supercluster

A cluster of clusters of galaxies.

supergiant

Large massive star of the greatest luminosity.

superior conjunction

Position of a superior planet, as viewed from Earth, when it is in the same direction as the Sun and farthest from Earth.

superior planet

Planet whose orbit lies outside Earth's orbit.

supernova

Exploding star that suddenly attains a luminosity up to 100 million times the Sun's brightness.

surface gravity

Acceleration at the surface of a body arising from its gravitational force.

S (seismic) waves

Transverse waves of an earthquake that cause Earth's material to vibrate perpendicular to the direction of the waves' travel. Also called secondary or shear waves.

synchronous

Locking of the rotation of a spinning body with its orbital revolution in which the rotation is an integer or simple fraction of its revolution.

synchrotron radiation

Continuous polarized radiation emitted by fast-moving electrons spiraling around the magnetic lines of force.

synodic month

Period of the Moon's phases, 29.53 days.

synodic period

Time between consecutive similar configurations of a planet; for example, between successive inferior conjunctions or oppositions.