question

absolute magnitude

answer

a scale for measuring the actual brightness of a celestial object without accounting for the distance of the object. measures how bright an object would appear if it were 10 parsecs (33 light years) away from earth.

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ablation

answer

a process where the atmosphere melts and removes the surface material of an incoming meteorite.

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accretion

answer

the process where dust and gas accumulate into larger bodies such as stars and planets.

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accretion disk

answer

a disk of gas that accumulates around a center of gravitational attraction, like a white dwarf, neutron star, or black hole. as the gas spirals in, it becomes hot and emits light or even x-rays.

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achondrite

answer

a stone meteorite that contains none of the small glassy spheres commonly found in meteorites.

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albedo

answer

the reflective property of non-luminous celestial objects.

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albedo feature

answer

a dark or light marking on the surface of an object that may or may not be a geological or topographical feature.

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altitude

answer

the angular distance of an object above the horizon.

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antimatter

answer

matter consisting of particles with charges opposite that of ordinary matter. its protons have a negative charge while electrons have a positive charge.

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antipodal point

answer

a point that is on the direct opposite side of a planet.

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apastron

answer

the point of greatest separation of two stars, such as in a binary star system.

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aperture

answer

the size of the opening through which light passes in an optical instrument such as a camera or telescope. a higher number = a smaller opening, while a lower number = a larger opening.

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aphelion

answer

the point in the orbit of a planet or other celestial body where it is farthest from the sun.

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apogee

answer

the point in the orbit of the moon or other satellite where it is farthest from the earth.

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apparent magnitude

answer

the apparent brightness of an object in the sky as it appears to an observer on earth. bright objects have a lower _____, while dim objects have a higher _____.

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asteroid

answer

a small planetary body in orbit around the sun, larger than a meteoroid but smaller than a planet.

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astrochemistry

answer

the branch of science that explores the chemical interactions between dust and gas interspersed between the stars.

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astronomical unit (au)

answer

a unit of measure equal to the average distance between the earth and the sun, approximately 93 million miles.

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atmosphere

answer

a layer of gases surrounding a planet, moon, or star.

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aurora

answer

a glow in a planet's ionosphere caused by the interaction between the planet's magnetic field and charged particles from the sun.

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aurora australis

answer

southern lights

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aurora borealis

answer

northern lights

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axis

answer

an imaginary line through the center of rotation of an object. aka the poles.

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azimuth

answer

the angular distance of an object around or parallel to the horizon from a predefined zero point (the direction of a celestial object from the observer).

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bar

answer

a unit of measure of atmospheric pressure.

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big bang

answer

the theory that suggests that the universe was formed from a single point in space during a cataclysmic explosion about 13.7 billion years ago.

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binary

answer

a system of two stars that revolve around a common center of gravity.

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black hole

answer

the collapsed core of a massive star. its gravitational pull is so strong that not even light can escape.

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blue shift

answer

indicates that an object is moving toward the observer. the larger the _____, the faster the object is moving.

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bolide

answer

a term used to describe an exceptionally bright meteor. they typically produce a sonic boom.

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caldera

answer

a type of volcanic crater that is extremely large, usually formed by the collapse of a volcanic cone or by a violent volcanic explosion.

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catena

answer

a series or chain of craters.

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cavus

answer

a hollow, irregular depression.

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celestial equator

answer

an imaginary line that divides the celestial sphere into a northern and southern hemisphere.

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celestial poles

answer

the north and south poles of the celestial sphere.

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celestial sphere

answer

an imaginary sphere around the earth on which the stars and planets appear to be positioned.

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cepheid variable

answer

a variable star whose light pulsates in a regular cycle. the period of fluctuation is linked to the brightness of the star. brigher ______ will have a longer period.

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chaos

answer

a distinctive area of broken terrain.

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chasma

answer

another name used to describe a canyon

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chondrite

answer

a meteorite that contains the small, glassy spheres commonly found in meteorites.

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chondrule

answer

small, glassy spheres commonly found in meteorites.

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chromosphere

answer

the part of the sun's atmosphere between the photosphere and the corona. contains high energy hydrogen atoms.

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corona

answer

the outer part of the sun's atmosphere. visible from earth during total solar eclipses.

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cosmic ray

answer

atomic nuclei (mostly protons) that are observed to strike the earth's atmosphere with extremely high amounts of energy.

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cosmic string

answer

a tube-like configuration of energy that is believed to have existed in the early universe.

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cosmogony

answer

the study of celestial systems, including the solar system, stars, galaxies, and galactic clusters.

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cosmology

answer

the study of the universe's origin, structure, and nature.

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crater

answer

a bowl-shaped depression formed by the impact of an asteroid or meteoroid.

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dark matter

answer

a term used to describe matter in the universe that cannot be seen, but can be detected by its gravitational effects on other bodies.

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debris disk

answer

a ring-shaped circumstellar disk of dust and debris in orbit around a star.

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declination

answer

the angular distance of an object in the sky from the celestial equator.

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density

answer

the amount of matter contained within a given volume. measured in grams per cubic centimeter.

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disk

answer

the surface of the sun or other celestial body projected against the sky.

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double asteroid

answer

two asteroids that revolve around each other and are held together by the gravity between them. aka binary asteroid.

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doppler effect

answer

the apparent change in wavelength of sound or light emitted by an object in relation to an observer's position. can be used to estimate an object's speed and direction.

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double star

answer

a grouping of two stars. this grouping can be apparent, where the stars seem close together, or physical, such as a binary system.

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dwarf planet

answer

a celestial body orbiting the sun that is massive enough to be rounded by its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite.

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eccentricity

answer

the measure of how an object's orbit differs from a perfect circle. eccentricity defines the shape of an object's orbit.

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eclipse

answer

when one celestial body passes into the shadow of another.

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eclipsing binary

answer

a binary system where one object passes in front of the other, cutting off some of all of its light.

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ecliptic

answer

an imaginary line in the sky traced by the sun as it moves in its yearly path through the sky.

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ejecta

answer

material from beneath the surface of a body such as a moon or planet that is ejected by an impact such as a meteor and distributed around the surface.

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electromagnetic radiation

answer

aka light. light waves created by fluctuations of electric and magnetic fields in space.

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electromagnetic spectrum

answer

the full range of frequencies, from radio waves to gamma waves, that characterizes light.

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ellipse

answer

an oval shape. Johannes Kepler discovered that the orbits of the planets were elliptical in shape rather than circular.

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elliptical galaxy

answer

a galaxy whose structure is smooth, shaped like an ellipse, and lacks complex structures such as spiral arms.

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elongation

answer

the angle between the sun and a planet, with earth as the reference point.

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ephemeris

answer

a table of data arranged by date. ______ tables are typically to list the positions of the Sun, Moon, planets, and other solar system objects.

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equinox

answer

the two points at which the sun crosses the celestial equator in its yearly path in the sky.

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escape velocity

answer

the speed required for an object to escape the gravitational pull of a planet or other body.

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event horizon

answer

the invisible boundary around a black hole past which nothing can escape the gravitational pull- not even light.

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evolved star

answer

a star that is near the end of its life cycle where most of its fuel has been used up. at this point, the star begins to lose mass in the form of stellar wind.

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extinction

answer

the apparent dimming of a star or planet when low on the horizon due to absorption by the earth's atmosphere.

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extragalactic

answer

a term that means outside of or beyond our own galaxy.

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extraterrestrial

answer

a term used to describe anything that does not originate on earth.

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eyepiece

answer

the lens at the viewing end of a telescope.

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faculae

answer

bright patches that are visible on the sun's surface, or photosphere.

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filament

answer

a strand of cool gas suspended over the photosphere by magnetic fields, which appears dark as seen against the disk of the sun.

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finder

answer

a small, wide field telescope attached to a larger telescope. the _____ is used to help point the larger telescope to the desired viewing location.

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fireball

answer

an extremely bright meteor. also known as bolides, they can be several times brighter than the full moon.

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flare star

answer

a faint red star that appears to change in brightness due to explosions on its surface.

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galactic halo

answer

the name given to the spherical region surrounding the center, or nucleus, of a galaxy.

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galactic nucleus

answer

a tight concentration of stars and gas found at the innermost regions of a galaxy. it is now believed that massive black holes may exist in some of these.

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galaxy

answer

a large grouping of stars. they are found in a variety of sizes and shapes.

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galilean moons

answer

the name given to jupiter's four largest moons; io, europa, callisto, and ganymede. discovered by galileo galilei and simon marius.

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gamma ray

answer

the highest energy, shortest wavelength form of electromagnetic radiation.

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geosynchronous orbit

answer

an orbit in which a satellite's orbital velocity is matched to the rotational velocity of the planet. a spacecraft in __________ appears to hang motionless above one position of a planet's surface.

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giant molecular cloud (gmc)

answer

massive clouds of gas in interstellar space composed primarily of hydrogen molecules. they have enough mass to produce thousands of stars and are frequently the sites of new star formation.

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globular cluster

answer

a tight, spherical grouping of hundreds of thousands of stars. they are composed of older stars, and are usually found around the central regions of a galaxy.

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granulation

answer

a pattern of small cells that be seen on the surface of the sun. they are caused by the convective motions of the hot gases inside the sun.

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gravitational lens

answer

a concentration of matter such as a galaxy or cluster of galaxies that bends light rays from a background object.

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gravity

answer

a mutual physical force of nature that causes two bodies to attract each other.

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greenhouse effect

answer

an increase in temperature caused when incoming solar radiation is passed but outgoing thermal radiation is blocked by the atmosphere.

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heliopause

answer

the point in space at which the solar wind meets the interstellar medium or solar wind from other stars.

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hydrogen

answer

an element consisting of one electron and one proton. the building block of the universe. stars form from massive clouds of ______.

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hubble's law

answer

the law of physics that states that the farther a galaxy is from us, the faster it is moving away from us.

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hydrostatic equilibrium

answer

a state that occurs when compression due to gravity is balanced by a pressure gradient which creates a force in the opposite direction. it is responsible for keeping stars from imploding and for giving planets their spherical shape.

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hypergalaxy

answer

a system consisting of a spiral galaxy surrounded by several dwarf white galaxies, often ellipticals. our galaxy and the andromeda galaxy are examples of this.

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inclination

answer

a measure of the tilt of a planet's orbital plane in relation to that of the earth.

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inferior conjunction

answer

occurs when an inferior planet is lined up directly between the earth and the sun.

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international astronomical union (iau)

answer

an international organization that unites national astronomical societies from around the world and acts as the internationally recognized authority for assigning designations to celestial bodies and their surface features.

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interplanetary magnetic field

answer

the magnetic field carried along with the solar wind.

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interstellar medium

answer

the gas and dust that exists in open spaces between the stars.qw

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ionosphere

answer

a region of charged particles in a planet's upper atmosphere.

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iron meteorite

answer

a meteorite that is composed mainly of iron mixed with smaller amounts of nickel.

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irregular galaxy

answer

a galaxy with no spiral structure and no symmetric shape. they are usually filamentary or very clumpy in shape.

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irregular satellite

answer

a satellite that orbits a planet far away with an orbit that is eccentric and inclined. they also tend to have retrograde orbits. believed to have been captured by the planet's gravity rather than being formed along with the planet.

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jansky

answer

the unit of strength of radio wave emission.

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jet

answer

a narrow stream of gas or particles ejected from an accretion disk surrounding a star or black hole.

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kelvin

answer

a unit of absolute temperature symbolized as K.

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kepler's first law

answer

a planet orbits the sun in an ellipse with the sun at one focus.

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kepler's second law

answer

a ray directed from the sun to a planet sweeps out equal areas in equal times.

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kepler's third law

answer

the square of the period of a planet's orbit is proportional to the cube of that planet's semi major axis; the constant of proportionality is the same for all planets.

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kiloparsec

answer

a distance equal to 1000 parsecs.

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kirkwood gaps

answer

regions in the main belt of asteroids where few or no asteroids are found

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kuiper belt

answer

a large ring of icy, primitive objects beyond the orbit of neptune. they are believed to be remnants of the original material that formed the solar system.

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lagrange point

answer

positions where the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them.

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lenticular galaxy

answer

a disk shaped galaxy that contains no conspicuous structure within the disk. tend to look more like elliptical galaxies than spiral galaxies.

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libration

answer

an effect caused by the apparent wobble of the moon as it orbits the earth. the moon always keeps the same side towards the earth, but due to _______, 59% of its surface can be seen over a period of time.

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light year

answer

an astronomical unit of measure equal to the distance light travels in a year, approximately 5.8 trillion miles.

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limb

answer

the outer edge or border of a planet or other celestial body.

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local group

answer

a small group of about 2 dozen galaxies of which our own milky way galaxy is a member.

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luminosity

answer

the amount of light emitted by a star.

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lunar eclipse

answer

a phenomenon that occurs when the moon passes into the shadow of the earth.

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lunar month

answer

aka lunation or synodic month. the average time between successive new or full moons. equal to 29 days, 12 hours, 44 minutes.

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lunation

answer

aka lunar month or synodic month. the average time between successive new or full moons. equal to 29 days, 12 hours, 44 minutes.

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magellanic clouds

answer

two small, irregular galaxies found just outside our milky way galaxies. they are visible in the skies of the southern hemisphere.

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magnetic field

answer

a condition found in the region around a magnet or electric current, characterized by the existence of a detectable magnetic force at every point in the region and by the existence of magnetic poles.

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magnetic pole

answer

either of two limited regions in a magnet at which the magnet's field is most intense.

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magnetosphere

answer

the area around a planet most affected by its magnetic field. the boundary of this field is set by the solar wind.

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magnitude

answer

the degree of brightness of a star or other object in the sky according to a scale on which the brightest star has a _____ -1.4 and the faintest visible star has _____ 6. sometimes referred to as apparent ______. each number is 2.5 times the brightness of the previous number.

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main belt

answer

the asteroid belt between mars and jupiter where most of the solar system's asteroids are found.

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major planet

answer

a name used to describe any planet that is considerably larger and more massive than the earth, and contains large quantities of hydrogen and helium.

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maria (singular: mare)

answer

a term used to describe a large, circular plane. means "sea". on the moon, the _______ are the smooth, dark colored areas.

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mass

answer

a measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies.

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matter

answer

anything that contains mass

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meridian

answer

an imaginary circle drawn through the north and south poles of the celestial equator.

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metal

answer

a term used by astronomers to describe all elements except hydrogen and helium.

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meteor

answer

a small particle of rock or dust that burns away in the earths atmosphere. aka shooting stars.

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meteor shower

answer

an event where a large number of meteors enter the earth's atmosphere from the same direction in space at nearly the same time. most take place when the earth passes through the debris left behind by a comet.

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meteorite

answer

an object, usually a chunk of metal or rock, that survives entry through the atmosphere to reach the earth's surface. meteors become _____s if they hit the ground.

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millibar

answer

a measure of atmospheric pressure equal to 1/1000th of a bar.

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minor planet

answer

a term used to describe objects, such as asteroids, that are in orbit around the sun but are not planets or comets. ex. dwarf planets, asteroids, comets, etc.

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molecular cloud

answer

an interstellar cloud of molecular hydrogen containing trace amounts of other molecules like carbon monoxide or ammonia.

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nadir

answer

a term used to describe a point directly underneath an object or body.

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nebula

answer

a cloud of dust and gas in space, usually illuminated by one or more stars. they represent the raw material the stars are made of.

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neutrino

answer

a fundamental particle produced by the nuclear reactions in stars. neutrinos are very hard to detect because the vast majority of them pass completely through the earth without interacting.

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neutron star

answer

a compressed core of an exploded star made up almost entirely of neutrons. they have a strong gravitational field and some, called pulsars, emit pules of energy along their axis.

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newton's first law of motion

answer

a body continues in its state of constant velocity unless it is acted on by an external force.

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nova

answer

a star that flares up to several times its original brightness for some time before returning to its original state.

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nuclear fusion

answer

the nuclear process whereby several small nuclei are combined to make a larger one whose mass is slightly smaller than the sum of the small ones. it is the reaction that fuels the sun, where hydrogen nuclei are fused to form helium.

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obliquity

answer

the angle between a body's equatorial plane and orbital plane.

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oblateness

answer

a measure of flattening at the poles of a planet or other celestial body.

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occultation

answer

an event that occurs when one celestial body conceals or obscures another.

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oort cloud

answer

a theoretical shell of comets that is believed to exist at the outermost regions of our solar system.

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open cluster

answer

a collection of young stars that formed together.

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opposition

answer

the position of a planet when it is exactly opposite the sun in the sky as seen from earth. a planet at _____ is at its closest approach to the earth and is best suitable for viewing.

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orbit

answer

the path of a celestial body as it moves through space.

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parallax

answer

the apparent change in position of two objects viewed from different locations.

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parsec

answer

equal to 3.26 light years.

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patera

answer

a shallow crater with a complex, scalloped edge.

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penumbra

answer

the area of partial illumination surrounding the darkest part of a shadow caused by an eclipse.

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perigree

answer

the point in the orbit of the moon or other satellite at which it is closest to the earth.

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perihelion

answer

the point in the orbit of a planet or other body where it is closest to the sun.

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perturb

answer

to cause a planet or satellite to deviate from a theoretically regular orbital motion.

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phase

answer

the apparent change in shape of the moon and inferior planets as seen from earth as they move in their orbits.

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photon

answer

a particle of light composed of a minute quantity of electromagnetic energy.

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photosphere

answer

the bright visible surface of the sun.

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planemo

answer

a large planet or planetary body that does not orbit a star. it is believed that most once orbited their mother star but were ejected from the star system by gravitational interaction with another massive object.

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planet

answer

a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighboring region of planetesimals.

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planetary nebula

answer

a shell of gas surrounding a small, white star. the gas is usually illuminated by the star, producing a variety of colors and shapes.

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planetesimal

answer

a solid object that is believed to exist in protoplanetary disks and debris disks. they are formed form small dust grains that collide and stick together and are the building blocks that eventually form planets in new planetary systems.

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planitia

answer

a low plain.

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planum

answer

a high plain or plateau.

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plasma

answer

a form of ionized gas in which the temperature is too high for atoms to exist in their natural state. it is composed of free electrons and free atomic nuclei.

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precession

answer

the apparent shift of the celestial poles caused by a gradual wobble of the earth's axis.

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prominence

answer

an explosion of hot gas that erupts from the sun's surface.

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prograde orbit

answer

planets have a _______ if the direction of its orbit is the same as that of the majority of other planets in the system.

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proper motion

answer

the apparent angular motion across the sky of an object relative to the solar system.

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protoplanetary disk

answer

a rotating circumstellar disk of dense gas surrounding a young newly formed star. it is thought that planets are eventually formed out of it.

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protostar

answer

dense regions of molecular clouds where stars are forming.

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pulsar

answer

a spinning neutron star that emits energy along its gravitational axis. this energy is received as pulses as the star rotates.

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quadrature

answer

a point in the orbit of a superior planet where it appears at right angles to the sun as seen from earth.

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quasar

answer

an unusually bright object found in the remote areas of the universe. they release incredible amounts of energy and are among the oldest and farthest objects in the known universe.

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quasi-stellar object

answer

a star-like object with a large redshift that gives off a strong source of radio waves. highly luminous and presumed to be extragalactic.

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radial velocity

answer

the movement of an object either towards or away from a stationary observer.

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radiant

answer

a point in the sky from which meteors in a meteor shower seem to originate.

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radiation

answer

energy radiated from an object in the form of waves or particles.

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radiation belt

answer

regions of charged particles in a magnetosphere.

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radio galaxy

answer

a galaxy that gives off large amounts of energy in the form of radio waves.

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red giant

answer

a stage in the evolution of a star where the fuel begins to exhaust and the star expands to about 50 times its normal size. the temperature cools, which gives the star a reddish appearance.

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red shift

answer

indicates that an object is moving away from the observer. the larger the _____, the faster the object is moving.

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regular satellite

answer

a satellite that orbits close to a planet in a nearly circular, equatorial orbit. believed to have been formed at the same time as the planet.

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resonance

answer

a state in which an orbiting object is subject to periodic gravitational perturbations by another.

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retrograde motion

answer

the phenomenon where a celestial body appears to slow down, stop, then move in the opposite direction. cause when the earth overtakes the body in its orbit.

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retrograde orbit

answer

the orbit of a satellite where the satellite travels in a direction opposite to the direction of the planet's rotation.

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right ascension

answer

the amount of time that passes between the rising of aries and another celestial object. right ascension is one unit of measure for locating an object in the sky.

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ring galaxy

answer

a galaxy with a ring-like appearance. the ring usually contains luminous blue stars. they are believed to have been formed by collisions with other galaxies.

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roche limit

answer

the smallest distance from a planet or other body at which purely gravitational forces can hold together a satellite or secondary body of the same mean density as the primart.

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rotation

answer

the spin of a body about its axis.

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satellite

answer

a natural or artificial body in orbit around a planet.

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seyfert galaxy

answer

a main-sequence star that rotates rapidly, causing a loss of matter to an ever-expanding shell.

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shell star

answer

a type of star which is believed to be surrounded by a thin envelope of gas, which is often indicated by bright emission lines in its spectrum.

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shepherd satellite

answer

a satellite that constrains the extent of a planetary ring through gravitational forces. also known as a shepherd moon.

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sidereal

answer

of, relating to, or concerned with the stars.

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sidereal month

answer

the average period of revolution of the moon around the earth in reference to a fixed star, equal to about 27 days.

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sidereal period

answer

the period of revolution of a planet around the sun or a satellite around its primary.

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singularity

answer

the center of a black hole, where the curvature of space time is maximal. at the singularity, the gravitational tides diverge. theoretically, no solid object can survive hitting the ______.

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small solar system body

answer

objects in the solar system that are neither planets nor dwarf planets (asteroids, comets, etc.)

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solar cycle

answer

the approximately 11-year variation in frequency or number of solar active events.

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solar eclipse

answer

a phenomenon that occurs when the earth passes into the shadow of the moon.

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solar flare

answer

a bright eruption of hot gas in the sun's photosphere.

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solar nebula

answer

the cloud of dust and gas out of which the solar system was believed to have formed about 5 billion years ago.

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solar wind

answer

a flow of charged particles that travels from the sun out into the solar system.

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solstice

answer

the time of year when the sun appears furthest north or south of the celestial equator.

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spectrometer

answer

the instrument connected to a telescope that separates the light signals into different frequencies, producing a spectrum.

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spectroscopy

answer

the technique of observing the spectra of visible light from an object to determine its composition, temperature, density, and speed.

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spectrum

answer

the range of colors that make up visible white light. it is produced when visible light passes through a prism.

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spicules

answer

grass-like patterns of gas seen in the atmosphere of the sun.

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spiral galaxy

answer

a galaxy that contains a prominent central bulge and luminous arms of gas, dust, and young stars that wind out from the central nucleus in a spiral formation.

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star

answer

a giant ball of hot gas that creates and emits its own radiation through nuclear fusion.

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star cluster

answer

a large grouping of stars, from a few dozen to a few hundred thousand, that are bound together by their mutual gravitational attraction.

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steady state theory

answer

the theory that suggests the universe is expanding but exists in a constant, unchanging state in the large scale. abandoned by most astronomers in favor of the big bang theory.

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stellar wind

answer

the ejection of gas from the surface of a star. aka solar wind. it is strongest near the end of a star's life.

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stone meteorite

answer

a meteorite that resembles a terrestrial rock and is composed of similar materials.

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stony iron

answer

a meteorite that contains regions resembling both a stone meteorite and an iron meteorite.

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sunspot

answer

areas of the sun's surface that are cooler than surrounding areas.

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supergiant

answer

the stage in a star's evolution where the core contracts and the star swells to about 500 times its original size.

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superior conjunction

answer

a conjunction that occurs when a superior planet passes behind the sun and is on the opposite side of the sun from the earth.

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superior planet

answer

a planet that exists outside the orbit of the earth.

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supernova

answer

a cataclysmic explosion caused when a star exhausts its fuel and ends its life. these are the most powerful forces in the universe. all of the heavy elements were created in these.

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supernova remnant

answer

an expanding shell of gas ejected at high speeds by a supernova explosion.

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synchronous rotation

answer

a period of rotation of a satellite about its axis that is the same as the period of its orbit around its primary, causing the satellite to always keep the same face to the primary. our moon is in _______ with the earth.

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synodic period

answer

the interval between points of opposition of a superior planet.

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tektite

answer

a small, glassy material formed by the impact of a large body, usually a meteor or asteroid.

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telescope

answer

an instrument that uses lenses and sometimes mirrors to collect large amounts of light from distant objects and enable direct observation and photography.

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terminator

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the boundary between the light side and dark side of a planet or other body.

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terrestrial

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anything originating on Earth.

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terrestrial planet

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a planet composed mainly of rock and iron, similar to that of earth.

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tidal force

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the differential gravitational pull exerted on any extend a force that occurs when the gravity pulling on one side of an object is larger than that on the other side, causing the object to stretch.

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tidal heating

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Frictional heating of a satellite's interior due to flexure caused by the gravitational pull of its parent planet and/or other neighboring satellites.

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transit

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the passage of a celestial body across an observer's meridian; also the passage of a celestial body across the disk of a larger one.

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trans-neptunian object (tno)

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any one of a number of celestial objects that orbit the sun at a distance beyond the orbit of the planet neptune.

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trojan

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an object orbiting in the lagrange points of another larger object.

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ultraviolet

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electromagnetic radiation at wavelengths shorter than the violet end of visible light. it can be deadly but earth's atmosphere effectively blocks most of it.

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umbra

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the area of total darkness in the shadow caused by an eclipse.

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universal time (ut)

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also known as greenwich mean time, this is the local time on the greenwich meridian. it is used by astronomers as a standard measure of time.

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van allen belts

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radiation zones of charged particles that surround the earth. the shape of them is determined by the earth's magnetic field.

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variable star

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a star that fluctuates in brightness

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visible light

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wavelengths of electromagnetic radiation that are visible to the human eye.

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virgo cluster

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a giant cluster of over 2000 galaxies that is located mainly within the constellation of virgo. it is located about 60 million light-years from earth.

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visual magnitude

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a scale used by astronomers to measure the visible brightness of a star or other celestial object.

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wavelength

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the distance between consecutive crests of a wave. serves as a unit of measure of electromagnetic radiation.

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white dwarf

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a very small, white star formed when an average sized star uses up its fuel supply and collapses. often produces a planetary nebula with the ______ at its center.

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x-ray

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electromagnetic radiation of a very short wavelength and very high energy. they have shorter wavelength than ultraviolet light.

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x-ray astronomy

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the field of astronomy that studies celestial objects by the x-rays they emit.

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x-ray star

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a bright celestial object that gives off x-rays as a major portion of its radiation.

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yellow dwarf

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an ordinary star such as the sun at a stable point in its evolution.

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zenith

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a point directly overhead from an observer.

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zodiac

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an imaginary belt across the sky in which the sun, moon, and all of the planets can always be found.

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zodiacal light

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a faint cone of light that can sometimes be seen above the horizon after sunset or before sunrise. it is caused by sunlight reflecting off small particles of material in the plane of the solar system.

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