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Flash Stuff:

 

Solar System

 

E (47)

 

Earth-approaching asteroid

An asteroid with an orbit that crosses the Earth's orbit or that will at some time cross the Earth's orbit as it evolves under the influence of the planets' gravity.

 

Eccentric

Noncircular; elliptical (applied to an orbit).

 

Eccentricity

A value that defines the shape of an ellipse or planetary orbit; the ratio of the distance between the foci and the major axis. Equivalently the eccentricity is (ra-rp)/(ra+rp) where ra is the apoapsis distance and rp is the periapsis distance.

 

Eclipse

The cutting off of light from one celestial body by another. It may also be the passage of all or part of one body through the shadow of another (e.g. a lunar eclipse in which the moon passes through the Earth's shadow).

 

Eclipsing Binary Star

A binary star in which the plane of revolution of the two stars in nearly edge-on to our line of sight, so that the light of one star is periodically diminished by the other passing in front of it.

 

Ecliptic

The plane of Earth's orbit about the Sun.

 

Eddington Limit
The theoretical limit at which the photon pressure would exceed the gravitational attraction of a light-emitting body. That is, a body emitting radiation at greater than the Eddington limit would break up from its own photon pressure.

 

Effective Temperature

The temperature of a star's outermost layer, the photosphere. Temperatures vary throughout a star, from millions of degrees in the core to thousands of degrees in the outer stellar atmosphere. Astronomers measure the temperature of the photosphere, and combine that with other information to calculate the core temperature.

 

Effusive Eruption

A relative quiet volcanic eruption which puts out basaltic lava that moves at about the speed one walks; the lava is fluid in nature; the eruptions at the Kilauea volcano on the island of Hawaii are effusive.

 

Einstein-Rosen Bridge

The "throat" of a black hole in one universe connecting up with one in a different universe; in theory, it is a bridge from one universe to another.

 

Ejecta

Material excavated from an impact crater, such as the blanket of material surrounding lunar craters and crater rays.

 

Electric Charge

This is the amount of electricity that an elementary particle with electricity holds within. The electric charge of electron, absolute value "e", is the basic unit. The electric charge of electron with minus electricity is -1. The electric charge of a proton is +1, and the electric charge of a neutron is 0.

 

Electromagnetic Force

One of the four fundamental forces or interactions of nature; the force that acts between charges and binds atoms and molecules together.

 

Electromagnetic Radiation

Radiation consisting of waves propagated through the building up and breaking down of electric and magnetic fields; these include radio, infrared, light, ultraviolet, x rays, and gamma rays.

 

Electromagnetic Spectrum

The whole array or family of electromagnetic waves, from radio to gamma rays.

 

Electromagnetic Waves (Radiation)
Another term for light. Light waves are fluctuations of electric and magnetic fields in space.

 

Electron
A negatively charged particle commonly found in the outer layers of atoms. The electron has only 0.0005 the mass of the proton.

 

Electron Volt
The change of potential energy experienced by an electron moving from a place where the potential has a value of V to a place where it has a value of (V+1 volt). This is a convenient energy unit when dealing with the motions of electrons and ions in electric fields; the unit is also the one used to describe the energy of X-rays and gamma-rays. A keV (or kiloelectron volt) is equal to 1000 electron volts. An MeV is equal to one million electron volts. A GeV is equal to one billion (109) electron volts. A TeV is equal to a million million (1012) electron volts.

 

Element

Any of more than 100 fundamental substances that consist of atoms of only one kind and that singly or in combination constitute all matter.

 

Elementary Particle

A particle that, it is believed, cannot be subdivided.

 

Ellipse

An oval. Johannes Kepler first discovered that the orbits of the planets are ellipses, not circles; he based his discovery on the careful observations of Tycho Brahe.

 

Elliptical Galaxy

A galaxy whose appearance resembles a solid made of a series of ellipses and that contains no conspicuous interstellar material.

 

Elliptical Orbit

An orbit in the shape of an elongated circle. All orbits are elliptical - a circle is just a special type of ellipse.

 

Elongation

The angle between a planet and the Sun in the sky. Greatest elongations refer to planets inside the Earth's orbit Venus and Mercury. The greatest elongation of Venus is 46 degrees east (evening star) or west (morning star) of the Sun, while Mercury is 23 degrees east or west of the Sun. For outer planets, see opposition and conjunction.

 

Emission Lines

Extra radiation at certain specific wavelengths in a spectrum, compared with neighboring wavelengths. These designate the presence of hot gas surrounding a star.

 

Emission Nebula

A gas cloud that receives energy from a hot star, allowing it to give off radiation in emission lines. These nebula are often very beautiful to look at. Many nebulae are both emission and absorption. Some examples are the Horsehead Nebula and the North America Nebula. See also: Absorption Nebula.

 

Emission Spectrum

A spectrum consisting of emission lines.

 

Emit

To send or give out.

 

Epicycle

A circular orbit of a body in the Ptolemaic system, the center of which revolves about another circle.

 

Epoch

An instant of time or a date selected as a point of reference for which are given values of the data under consideration, which vary with the time.

 

Equator

A circle or circular band dividing the surface of a body into two usually equal and symmetrical parts.

 

Equinox

The two points at which the sun crosses the celestial equator; the spring equinox is about March 21, and the autumnal equinox is about September 22.

 

Ergosphere

Region surrounding a spinning black hole, between the static limit and the outer event horizon, in which it is impossible to be at rest.

 

erg/sec
A form of the metric unit for power. It is equal to 10-10 kilowatts (see scientific notation).

 

Escape Velocity

Speed a body needs to travel in order to escape the surface gravity of a star or planet. A rocket launched from Kennedy Space Center must accelerate to 11.18 km/s, or 18,300 m.p.h. to escape Earth's gravitational pull.

 

Eucrite Meteorite

One of a class of basaltic meteorites believed to have originated on the asteroid Vesta.

 

Event

A point in space-time, specified by its time and place.

 

Event Horizon

The "edge" of a black hole: and imaginary surface where the escape velocity reaches the speed of light.

 

Evolved Star
A star near the end of its lifetime when most of its fuel has been used up. This period of the star's life is characterized by loss of mass from its surface in the form of a stellar wind.

 

Exclusion Principle

Quantum mechanical principle by which no two particles of the same kind can have the same position and momentum/velocity.

 

Explosive Eruption

A dramatic volcanic eruption which throws debris high into the air for hundreds of miles; lava is low in silicate; can be very dangerous for people near by; an example is Mount St. Helens in 1980.

 

Exponential Notation

'1.23e3' means '1.23 times 10 to the third power or 1,230'; '4.56e-7' means '4.56 divided by 10 to the seventh power' or 0.000000456.

 

Extinction

Reduction of the light from a celestial body produced by the Earth's atmosphere, or by interstellar absorption.

 

Extragalactic

Beyond our own Milky Way Galaxy.

 

Extrasolar

Not belonging to the Sun - outside the solar system.

 

Extraterrestrial

Not belonging to the Earth.

 

Eyepiece

A magnifying lens used to view the image produced by the objective of a telescope.

 

 

F (24)

 

Faculae

A bright region of the photosphere seen in white light, seldom visible except near the solar limb.

 

Farrum

Pancake-like structure.

 

Fast Fourier Transformation (FFT)
A Fourier Transform is the mathematical operation that takes measurements made with a radio interferometer and transforms them into an image of the radio sky. The Fast Fourier Transform is technique used by computer programs that allows the Fourier Transform to be computed very quickly.

 

Fermi Acceleration
In order to explain the origins of cosmic rays, Enrico Fermi (1949) introduced a mechanism of particle acceleration, whereby charged particles bounce off moving interstellar magnetic fields and either gain or lose energy, depending on whether the "magnetic mirror" is approaching or receding. In a typical environment, he argued, the probability of a head-on collision is greater than a head-tail collision, so particles would be accelerated on average. This random process is now called 2nd order Fermi acceleration, because the mean energy gain per "bounce" is dependent on the "mirror" velocity squared. Bell (1978) and Blandford and Ostriker (1978) independently showed that Fermi acceleration by supernova remnant (SNR) shocks is particularly efficient, because the motions are not random. A charged particle ahead of the shock front can pass through the shock and then be scattered by magnetic inhomogeneities behind the shock. The particle gains energy from this "bounce" and flies back across the shock, where it can be scattered by magnetic inhomogeneities ahead of the shock. This enables the particle to bounce back and forth again and again, gaining energy each time. This process is now called 1st order Fermi acceleration, because the mean energy gain is dependent on the shock velocity only to the first power.

 

Field

Something that exists throughout space and time, as opposed to a particle that exists at only one point at a time.

 

Filament

A strand of cool gas suspended over the photosphere by magnetic fields, which appears dark as seen against the disk of the Sun; a filament on the limb of the Sun seen in emission against the dark sky is called a prominence.

 

Finder

A small, low-power telescope attached to and aligned with a larger one; its wider field of view makes it useful for locating celestial objects.

 

Fireball

Any meteor brighter than Venus, about magnitude –4.

 

Fission

The breakup of a heavy atomic nucleus into two or more lighter ones.

 

Fissure

A narrow opening or crack of considerable length and depth.

 

Flare

A sudden eruption of energy on the solar disk lasting minutes to hours, from which radiation and particles are emitted.

 

Flare Star

A faint red star that has short-lived explosions on its surface; these explosions cause the star to appear temporarily brighter.

 

Flexus

Cuspate (pointed) linear feature.

 

Fluctus

Flow terrain.

 

Flux

The rate at which energy or matter crosses a unit area of a surface.

 

Flyby

An encounter between a probe and a planet, comet, or asteroid, in which the probe doesn't stop to orbit or land.

 

Focal Length

The distance between a lens or mirror and its focal point. This length is usually stated in terms of the lens or mirror diameter f/4 means that the focal length is four times the diameter of the optic.

 

Focus

A point, or focal point, where a lens or mirror directs light. In a telescope, astronomers place an eyepiece close to the focus in order to project the telescope focal point onto an observers eye (retina). Thus, an image looks "focused."

 

Forbidden Lines

Spectral lines that are not usually observed under laboratory conditions because they result from atomic transitions that are highly improbable.

 

Fossa

Long, narrow, shallow depression.

 

Fraunhofer Line

An absorption line in the spectrum of the Sun or of a star.

 

Fraunhofer Spectrum

The array of absorption lines in the spectrum of the Sun or a star.

 

Frequency

Because sounds and electromagnetic waves are waves, it vibrates up and down regularly. Frequency is how many times it vibrates in a second. Unit is Hertz (Hz) etc.

 

Fusion

1: The process of blending by melting together.

2: Becoming fluid with heat.

 

 

G (31)

 

Gaia Hypothesis

Named for the Greek Earth goddess Gaea, holds that the Earth as a whole should be regarded as a living organism and that biological processes stabilize the environment. First advanced by British biologist James Lovelock in 1969.

 

Galactic Cannibalism

The process by which a larger galaxy strips material from a smaller one.

 

Galactic Cluster

An "open" cluster of stars located in the spiral arms or disk of the Galaxy.

 

Galactic Halo
A spherical region surrounding the center of a galaxy. This region may extend beyond the luminous boundaries of the galaxy and contain a significant fraction of the galaxy's mass. Compared to cosmological distances, objects in the halo of our galaxy would be very nearby.

 

Galaxy

One of billions of systems each including stars, nebulae, star clusters, globular clusters, and interstellar matter that make up the universe.

 

Galilean Moons

Jupiter's four largest moons: Io, Europa, Ganymede and Callisto; discovered independently by Galileo and Marius.

 

Gamma-Ray

Electromagnetic radiation with energy greater than several hundred thousand electron volts. Usually, they are thought of as any photons having energies greater than about 100 keV.

 

Gamma-Ray Burst (GRB)
Plural is GRBs. A burst of gamma-rays from space lasting from a fraction of a second to many minutes. There is no clear scientific consensus as to their cause or even their distance.

 

Gas Giant

A large planet that is made largely of a very deep, dense gaseous atmosphere.

 

Gegenschein

A round or elongated spot of light in the sky at a point 180 degrees from the Sun. Also called counterglow.

 

General Relativity Theory

A theory advocated by Einstein in 1915. Together with special theory of relativity advocated in 1905, is famous for relativity theory. It explains distortion of time and space due to gravitation. See also Relativity, General Theory of

 

Geosynchronous Orbit

A direct, circular, low-inclination orbit 35,880km above the equator in which the satellite's orbital velocity is matched to the rotational velocity of the planet; a spacecraft appears to hang motionless above one position of the planet's surface.

 

Giant

A star that is especially bright and large for its color/temperature. Many stars become red giants late in their life and some even become supergiants.

 

Giant Molecular Cloud (GMC)
Massive clouds of gas in interstellar space composed primarily of hydrogen molecules (two hydrogen atoms bound together), though also containing other molecules observable by radio telescopes. These clouds can contain enough mass to make several million stars like our Sun and are often the sites of star formation.

 

Giant Star

A star that has reached the last stages of its evolution, has swollen in size, increased in brightness, and changed in color. Sunlike stars become red giants; stars with more than ten times the mass of the Sun become supergiants, stars with the most luminosity in the universe.

 

Globular Cluster

A spherical cluster of stars of a common origin. These stars and clusters are often very old.

 

Grand Unification Energy

The energy above which, it is believed, the electromagnetic force, weak force, and strong force become indistinguishable from each other.

 

Grand Unified Theory (GUT)

A theory that unifies the electromagnetic, strong, and weak energy forces.

 

Granulation

A pattern of small cells seen on the surface of the Sun caused by the convective motions of the hot solar gas.

 

Gravitational Collapse
When a massive body collapses under its own weight. (For example, interstellar clouds collapse to become stars until the onset of nuclear fusion stops the collapse.)

 

Gravitational Lens

A configuration of celestial objects, one of which provides one or more images of the other by gravitationally deflecting its light.

 

Gravitationally Bound
Objects held in orbit about each other by their gravitational attraction. For example, satellites in orbit around the earth are gravitationally bound to Earth since they can't escape Earth's gravity. By contrast, the Voyager spacecraft, which explored the outer solar system, was launched with enough energy to escape Earth's gravity altogether, and hence it is not gravitationally bound.

 

Gravitational Radius
See event horizon.

 

Gravitational Red Shift

The red shift of electromagnetic radiation caused by a gravitational field. The slowing of clocks in a gravitational field.

 

Gravitational Well

The distortion of space and time caused by the gravity of a massive object such as a star..

 

Gravity

The most feeble of the four fundamental forces in the universe that affect all matter. Gravity is an attractive force. The magnitude of gravitational attraction depends directly on mass and inversely on distance squared. For instance, the gravitational attraction between you and the Earth is much greater than that between you and the Sun, even though the Sun is far more massive than the Earth (333,000 times). The distance separating you from the Sun weakens the mutual gravitational attraction so that the Earth's gravitational pull on you at Earth's surface is 1653 times greater than the Sun's.

 

Gravity Waves

Ripples in space-time created by the stretching and squeezing effects of massive objects, notably supernovae, orbiting black holes, and orbiting neutron stars. Gravity waves are transverse waves they stretch and squeeze space-time in directions perpendicular to the wave's motion. Einstein's theory of general relativity forecasts their existence, but they have not yet been detected.

 

Great Red Spot

A raging red swirling storm located in Jupiter's upper atmosphere. The storm has been observed for the last 300 years, and appears to rotate counterclockwise like a hurricane once every six days. During the 1979 Voyager II encounter with Jupiter, the Red Spot measured 10,000 by 20,000 kilometers.

 

Greatest Elongation

The maximum separation between Mercury or Venus and the Sun in the sky. Venus or Mercury peaks as an "evening star" at its greatest eastern elongation, and as a "morning star" during its greatest western elongation. The geometry of these arrangements is a line tangent to the orbit of Venus or Mercury that intersects Earth and Venus, or Earth and Mercury.

 

Greenhouse Effect

An increase in temperature caused when the atmosphere absorbs incoming solar radiation but blocks outgoing thermal radiation; carbon dioxide is the major factor.

 

Guest Star
The ancient Chinese term for a star that newly appears in the night sky, and then later disappears. Later, the Europeans called this a nova.