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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.
Noncircular; elliptical (applied to an orbit).
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.
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).
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.
The plane of Earth's orbit about the Sun.
Eddington
Limit
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.
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.
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.
Material
excavated from an impact crater, such as the blanket of material surrounding
lunar craters and crater rays.
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.
One of the
four fundamental forces or interactions of nature; the force that acts between
charges and binds atoms and
molecules together.
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.
The whole array or family of electromagnetic waves, from radio to gamma rays.
Electromagnetic
Waves (Radiation)
Electron
Electron
Volt
Any of more than 100 fundamental substances that consist of atoms of only one kind and that singly or in combination constitute all matter.
A particle that, it is believed, cannot be subdivided.
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.
A galaxy whose appearance resembles a solid made of a series of ellipses and that contains no conspicuous interstellar material.
An orbit in the shape of an elongated circle. All orbits are elliptical - a circle is just a special type of ellipse.
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.
Extra radiation at certain specific wavelengths in a spectrum, compared with neighboring wavelengths. These designate the presence of hot gas surrounding a star.
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.
A spectrum consisting of emission lines.
To send or give out.
A circular orbit of a body in the Ptolemaic system, the center of which revolves about another circle.
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.
A circle or circular band dividing the surface of a body into two usually equal and symmetrical parts.
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.
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
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.
One of a class of basaltic meteorites believed to have originated on the asteroid Vesta.
A point in space-time, specified by its time and place.
The "edge" of a black hole: and imaginary surface where the escape velocity reaches the speed of light.
Evolved
Star
Quantum mechanical principle by which no two particles of the same kind can have the same position and momentum/velocity.
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.
'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.
Reduction of the light from a celestial body produced by the Earth's atmosphere, or by interstellar absorption.
Beyond our own Milky Way Galaxy.
Not belonging to the Sun - outside the solar system.
Not belonging to the Earth. A magnifying lens used to view the image produced by the objective of a telescope.
A bright region of the photosphere seen in white light, seldom visible except near the solar limb.
Pancake-like structure.
Fast
Fourier Transformation (FFT)
Fermi
Acceleration
Something that exists throughout space and time, as opposed to a particle that exists at only one point at a time.
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.
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.
Any meteor brighter than Venus, about magnitude –4.
The breakup of a heavy atomic nucleus into two or more lighter ones.
A narrow opening or crack of considerable length and depth.
A sudden eruption of energy on the solar disk lasting minutes to hours, from which radiation and particles are emitted.
A faint red star that has short-lived explosions on its surface; these explosions cause the star to appear temporarily brighter.
Cuspate (pointed) linear feature.
Flow terrain.
The rate at which energy or matter crosses a unit area of a surface.
An encounter between a probe and a planet, comet, or asteroid, in which the probe doesn't stop to orbit or land.
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.
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."
Spectral lines that are not usually observed under laboratory conditions because they result from atomic transitions that are highly improbable.
Long, narrow, shallow depression.
An absorption line in the spectrum of the Sun or of a star.
The array of absorption lines in the spectrum of the Sun or a star.
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.
1: The process of blending by melting together. 2: Becoming fluid with heat.
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.
The process by which a larger galaxy strips material from a smaller one.
An "open" cluster of stars located in the spiral arms or disk of the Galaxy.
Galactic
Halo
One of billions of systems each including stars, nebulae, star clusters, globular clusters, and interstellar matter that make up the universe.
Jupiter's four largest moons: Io, Europa, Ganymede and Callisto; discovered independently by Galileo and Marius.
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)
A large planet that is made largely of a very deep, dense gaseous atmosphere.
A round or elongated spot of light in the sky at a point 180 degrees from the Sun. Also called counterglow.
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
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.
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)
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.
A spherical cluster of stars of a common origin. These stars and clusters are often very old.
The energy above which, it is believed, the electromagnetic force, weak force, and strong force become indistinguishable from each other.
A theory that unifies the electromagnetic, strong, and weak energy forces.
A pattern of small cells seen on the surface of the Sun caused by the convective motions of the hot solar gas.
Gravitational
Collapse
A configuration of celestial objects, one of which provides one or more images of the other by gravitationally deflecting its light.
Gravitationally
Bound
Gravitational
Radius
The red shift of electromagnetic radiation caused by a gravitational field. The slowing of clocks in a gravitational field.
The distortion of space and time caused by the gravity of a massive object such as a star..
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.
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.
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.
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.
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 |