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A side-looking imaging system that uses the Doppler effect to sharpen the effective resolution in the cross-track direction.
1: A moon revolving around a larger planet. 2: A man-made object rocketed into orbit around the earth, the moon,
etc. Persisting over a long period of time.
A line of cliffs produced by faulting or erosion; a relatively straight, cliff-like face or slope of considerable linear extent, breaking the general continuity of the land by separating surfaces lying at different levels.
A telescope with a camera fixed at prime focus. Schmitt telescopes are able to take bright, wide-angle pictures of the sky.
Schwarzschild
Black Hole
The distance between the central singularity and event horizon of a black hole. The length of the Schwarzschild Radius depends on the mass of the black hole. Anything inside this radius will not escape the black hole.
Scientific
Notation
Second
(s)
One-half of the longest dimension of an ellipse.
Sensitivity
The search for extraterrestrial intelligence, usually applied to searches for radio signals from other civilizations.
An energetic galaxy with an exceptionally bright core that emits non-thermal (not star light) radiation. Carl Seyfert first observed these peculiar galaxies in 1943. The majority of Seyfert galaxies have a spiral structure and vary in brightness on the order of months. This indicates a small energy source (perhaps a black hole) at the nucleus that is responsible for the non-thermal radiation. Seyfert galaxy luminosity varies between one-tenth and ten times the luminosity of our galaxy.
A satellite that constrains the extent of a planetary ring through gravitational forces.
The production of irreversible chemical or physical changes in rocks by a shock wave generated by impact, or detonation of high-explosive or nuclear devices.
Shock
Wave
Of, relating to, or expressed in relation to stars or constellations.
A clock that measures sidereal time, from 0 to 24 sidereal hours. This clock measures time with respect to the motion of stars, not the Sun: One sidereal day equals 24 sidereal hours equals 23.9345 solar mean hours equals 23 hours, :56 minutes, and 4.091 seconds in mean solar time. Thus, a sidereal clock ticks just a bit faster than a solar mean clock. The difference between solar and sidereal time depends on the apparent motion of stars or the apparent motion of the Sun in the sky.
The average period of revolution of the moon around the earth in reference to a fixed star, equal to 27 days, 7 hours, 43 minutes in units of mean solar time.
The time, relative to the stars, needed for a planet or moon to make one rotation or revolution around its primary body.
Rotation time measured with respect to the fixed stars rather than the Sun or body orbited.
Measurement of time based on the position of the vernal equinox instead of the Sun. A sidereal clock does not suffer the irregularities of a solar clock caused by Earth's elliptical orbit. A sidereal clock tracks sidereal time from 0 to 24 sidereal hours. The time reading on the sidereal clock equals the right ascension meridian that lies at the zenith, directly overhead. Astronomers prefer this time keeping method, because sidereal time is fixed to stars. An astronomer compares the right ascension of an object and sidereal time to figure out the optimum observing time.
A compound containing silicon and oxygen (e.g. olivine).
A theoretical point at the core of a black hole, where the curvature of space-time is infinite. Einstein's General Theory of Relativity predicts that such points, which could be cosmic potholes to advanced space travelers, may exist in the space and time of our universe. Anything falling into a black hole meets certain doom. Once past the black hole's event horizon, the curvature of space-time is so great that nothing can escape -- not even light. Beyond the event horizon, space-time curvature increases toward the singularity. Gravitational tidal forces also are unimaginably strong and will shred anything into it's elemental atoms.
A theorem that shows that a singularity must exist under certain circumstances - in particular, that the universe must have started with a singularity.
Literally "bay"; really a small plain.
The approximately 11-year, quasi-periodic variation in the frequency or number of solar active events.
An arrangement (in order) of the Earth, Moon, and Sun where the Moon blocks the light from the Sun to an observer on Earth. The Moon's shadow does not completely contain the Earth. Only a narrow shadow cone of totality sweeps across the Earth's surface (umbra) surrounded by a partial shadow (penumbra). The solar eclipse alignment of Earth, Moon and Sun does not occur every month, because the Moon's orbit is tilted five degrees from a plane containing the Earth and Sun.
A filter that reduces the sun's light to a level where you can view it with a telescope; only those filters which fit over a telescope's objective are safe to use.
A violent eruption of plasma from the chromosphere whipped up by intense magnetic activity. Temperatures quickly soar to 20 million degrees as the flare rises thousands of kilometers above the chromosphere. Large flares release 10^25 Joules, or about the energy of a few million volcanic eruptions on the Earth. Sunspots and solar-flare frequency are strongly related. Flares often disturb the atmosphere electrically, thus interfering with radio transmissions. The aurora borealis and aurora australis is a result of flare activity injecting energetic particles into Earth's magnetic field.
Turbulent cells in the photosphere of sun, giving the sun an
irregular, mottled appearance. A direct relation in how much mass an object has compared to the sun (for example, if a star has a mass of 1.4 solar masses, then it is 1.4 x mass of the sun) . 1
solar mass = 1 Msun = 2 x 1033 grams. The large cloud of gas and dust from which the Sun and planets condensed 4.6 billion years ago.
The sun with the group of celestial bodies that are held by its attraction and revolve around it. A tenuous flow of gas and energetic charged particles, mostly protons and electrons plasma which stream from the Sun; typical solar wind velocities are almost 350 kilometers (217 miles) per second.
Either of two points on the celestial sphere where the Sun reaches its maximum distances north and south of the celestial equator; time of the year when the daylight is the longest or the shortest.
A four-dimensional coordinate system, or reference frame, with three space axis (x, y, z) and one time axis (t). A point in this reference frame is called an event, something that happens in space and time. Physicists and astrophysicists prefer a space-time reference frame to visualize complex events and interactions. Einstein explained that a constant exists between all reference frames, regardless of their motion relative to each other.
Any of the tree dimensions that are space-like - that is, any except the time dimension (i.e. length, width, depth).
Einstein's rejection of the Newtonian notion of absolute space and time, based on the observation that the speed of light is independent of the motion of an observer. No matter how fast someone runs toward you with a flashlight, you will always measure c, 3 x 10^8 m/s, as the speed of light that the flashlight emits. From this foundation, Einstein constructed a revolutionary model of gravity and a universe full of unexpected surprises like black hole, gravity waves, time dilation, and the equivalence of mass and energy: E=MC2. Astronomers and astrophysicists regularly make use of the theoretical tools of special relativity to interpret and analyze light. For instance, astronomers rely on Doppler shift measurements to calculate the motions of stars and galaxies. Special Relativity is the concept tool of the calculation, relating a wavelength shift to the velocity of the source.
The study of spectral lines to reveal information about the composition of a star or galaxy, or to find its redshift.
Bright or dark lines in the spectrum of a body emitting radiation. See also: absorption line and emission line.
A method of classifying stars according to their color and surface temperature.
An instrument used to measure
wavelengths or indexes of
refraction. An instrument used for splitting starlight into a spectrum and revealing spectral lines that tell astronomers about the composition of the universe.
Spectroscopic
Parallax
Astronomers seek the recipe of stars, galaxies, and other celestial objects through spectroscopy. Because each atomic element absorbs and emits light in a unique set of wavelengths, the astronomer can sift through the spectrum of a star and determine what elements are present in the star's atmosphere. The spectrum is evidence of whatever is glowing, or radiating light. With spectroscopy astronomers relate the appearance of the spectrum to the physical processes inside the star. From the shapes and depths of spectral lines, the astronomer can calculate fundamental qualities of a star, like how fast the gases churn through the stellar atmosphere, or the star's effective temperature. An astronomer may also be interested in correlations between the amounts (abundance) of certain elements and the physical behavior of the star, or the age of the star, or the abundances of other elements. For instance, compared with the Sun, stars with low amounts of iron are also low in almost every other element with respect to hydrogen. Perhaps you have wondered why stars appear in colors from red to blue and white. These are the dominant colors of the star's spectrum, where the star radiates most of its energy. Effective temperature, or the temperature of the stars photosphere, is related to the color of the star. Stars with cooler stellar atmospheres than our Sun appear orange and red. Those with hotter temperatures are blue and white In addition, stars that convert hydrogen into helium and energy in their cores (main sequence stars) show a relation with mass. Hot main sequence stars are more massive than cool main sequence stars. This correlation does not apply once the star "burns up" its primary hydrogen fuel, and evolves off the main sequence.
Plural: Spectra. An array of the components of an emission or wave separated and arranged in the order of some varying characteristic (as wavelength, mass, or energy) (such as the light spectrum).
A measure of how far a ray of light travels in one second - nearly 299,792,458m (186,000 miles/second). Nothing can travel faster than this speed.
1: A globular body; ball.
A structural component of the chromosphere that erupts like a plasma geyser driven by dense magnetic fields. Spicules rise between 3,000 and 10,000 kilometers above the magnetic mesh beneath. At the boundary between the photosphere and chromosphere, spicules look like peach fuzz. Spicules live short, dynamic lives of a few minutes but spew plasma at speeds of more than ten kilometers a second.
Spiral Galaxy
Star
A galaxy that has undergone a sudden period of star formation, often as the result of colliding with another galaxy.
Star Cluster
A now-discredited theory that the universe has no beginning and no end, and will remain the same forever.
Stefan-Boltzmann Constant (Sigma) The constant of proportionality present in the Stefan-Boltzmann law. It is equal to 5.6697 x 10-8 Watts per square meter per degree Kelvin to the fourth power (see scientific notation).
Stars given a designation consisting of a letter and a number according to the nature of their spectral lines which corresponds roughly to surface temperature. The classes are: O, B, A, F, G, K, and M; O stars are the hottest; M the coolest. The numbers are simply subdivisions of the major classes. The classes are oddly sequenced because they were assigned long ago before we understood their relationship to temperature. O and B stars are rare but very bright; M stars are numerous but dim. The Sun is designated G2.
Hipparcos firstly thought it of in Greek time, and in mid-19th century this unit of the brightness of stars was set. The stars are brighter if their magnitude is small, and a star of the first magnitude has 100 times more brightness than a star of 6th magnitude. For every one brighter magnitude, the brightness becomes 2.5 times brighter. For stars brighter than a star of the first magnitude, you would use minus signs such as, 0 magnitude, -1 magnitude, and -2 magnitude. There are distinctions between, Apparent magnitude and absolute magnitude.
A black hole produced by the explosion of a massive star as a supernova; most weigh about ten solar masses.
Stellar
Wind
Steradian
(sr)
The cold region of a planetary atmosphere above the convecting regions (the troposphere), usually without vertical motions but sometimes exhibiting strong horizontal jet streams.
A theory of physics in which particles are described as waves on strings; strings have length but no other dimension.
The strongest of the four fundamental forces, with the shortest range of all; it holds the quarks together within protons and neutrons, and holds the protons and neutrons together to form atoms.
Any particle smaller than an atom. Protons, neutrons, and electrons are the main subatomic particles that make up atoms.
Sublimation occurs when a substance changes directly from a solid to a gas without becoming liquid.
Sub-parallel furrows and ridges.
An area seen as a dark spot on the photosphere of the Sun. Sunspots are concentrations of magnetic flux, typically occurring in bipolar clusters or groups. They appear dark because they are cooler than the surrounding photosphere.
An enormous chain of galaxies linked by their mutual gravity. Superclusters look as if they ride on the surfaces of bubbles. Our galaxy is a peripheral member of the Virgo Supercluster, centered around a giant elliptical galaxy M87. Luminous matter does not bind this cluster: Dark matter outweighs luminous matter 10 to 1. Our galaxy seems to be drifting toward the Virgo Supercluster at about 250 km/s.
Supergiant
The planets Mars, Jupiter, Saturn, Uranus, Neptune and Pluto are superior planets because their orbits are farther from the Sun than Earth's orbit.
A black hole located at the center of a galaxy; these holes, formed by material falling onto the galaxy's core, may weight billions of solar masses.
Supernova
The remainder of the stellar atmosphere that the supernova blows away into interstellar space. Astronomers see spectral emission of elements processed in the late stages of stellar evolution, like nitrogen, oxygen, and neon. The material is still hot and rushes through space at hundreds of kilometers per second.
The orbital radius at which the satellite's orbital period is equal to the rotational period of the planet. A synchronous satellite with an orbital inclination of zero (same plane as the planet's equator) stays fixed in the sky from the perspective of an observer on the planet's surface. These orbits are commonly used for communications satellites).
A satellite's rotational period is equal to its orbital period; this causes the same side of a satellite to always face the planet. Synchronous rotation occurs when a planet's gravity produces a tidal bulge in its satellite. The gravitational attraction and bulge acts like a torque, which slows down the satellite until it reaches a synchronous rotation.
An accelerator in which charged particles are accelerated around a fixed circular path by a radio-frequency potential and held to the path by a time-varying magnetic field.
Synchrotron Radiation
Systéme
Internationale d'Unités (SI)
Tangential
(Transverse) Velocity
The surface rocks that an asteroid or comet impact.
Deformation forces acting on a planet's crust.
1: A usually tubular optical instrument for viewing distant objects by means of the refraction of light rays through a lens of reflection that is a concave mirror. 2: A tube that contains a mirror (or mirrors) that help magnify an object that is far away.
Temperature
A hard, shadow edge marking the boundary between the night and day side of a moon or planet. Along this jagged boundary on the Moon, you can clearly see another dimension to mountains and crater. Sometimes, towering crater rings still catch a bit of sunlight as they slip behind the terminator.
Extensive land mass.
Included in this group are the planets Mercury, Venus, Earth, and Mars. They are classified as terrestrial planets because of there compact, rocky, Earth-like appearance.
Tile; terrain formed of polygonal pattern.
A set of hypotheses and laws that have been well demonstrated to apply to a wide range of phenomena associated with a particular subject.
General term for "Special theory of relativity" suggested by Einstein in 1905 and "General relativity" suggested in 1915. Special theory of relativity says that light speed never changes. General relativity says that gravitation distorts space and time.
A star's light or photon engine. Every star on the main sequence converts mass into energy through thermonuclear fusion. The process demands high temperature and pressure in order to fuse the hydrogen into helium, due to powerful electromagnetic forces separating neighboring H atoms.
A reaction of or relating to the transformation in the nucleus of atoms of low atomic weight (as hydrogen) that require a very high temperature for their inception (beginning), as in the sun.
Radiation of or relating to, or caused by heat.
Small domical mountain or hill.
The gravitational pull on planetary objects from nearby planets and moons. When the tidal forces of a planet and several moons are focused on certain moons, particularly if the orbits of the various objects bring them into alignment on a repeated basis, the tidal forces can generate a tremendous amount of energy within the moon. The intense volcanic activity of Io is the result of the interaction of such tidal forces.
The frictional heating of a satellite's interior due to flexure caused by the gravitational pull of its parent planet and possibly neighboring satellites.
Time
Dilation
The time at which a celestial object is highest in the sky. This is the best time to view the object. At transit, the object's light travels through the thinnest possible layer of Earth's atmosphere, which can distort an object's appearance. At times of rise and set, when an object is nearest the horizon, its light travels through the most atmosphere.
Transition Region
(also "Trekker") A devotee of the science fiction program Star Trek.
1,000,000,000,000.
Two neutrons are added to atomic nucleus of hydrogen. One proton and 2 neutrons form an atomic nucleus and one electron is flying around it. Atomic number (number of protons in atomic nucleus) is 1. Atomic weight (Sum of number of protons and number of neutrons in an atomic nucleus, index of weight) is 3. With atom, the placing of electrons affect the characteristic greatly, so this matter shows similar characteristic to hydrogen.
An object orbiting in the Lagrange points of another (larger) object. This name derives from a generalization of the names of some of the largest asteroids in Jupiter's Lagrange points: 588 Achilles, 624 Hektor, and 911 Agamemnon. Saturn's satellites Helene, Calypso and Telesto are also sometimes called Trojans.
The lower regions of a planetary atmosphere where convection keeps the gas mixed and maintains a steady increase of temperature with depth. Most clouds are in the troposphere.
Turbulence |