Science vocabulary answers
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- science: process used to investigate the world an provide some
possible answers to scientific problems.
- scientific method: approaches taken to try and solve a problem;
recognize a problem, form a hypothesis, test hypothesis, analyze data, draw
- hypothesis: prediction about a problem that can be tested; based on
observations, new information, and personal experience, and often written as
an if-and-the statement.
- theory: explanation backed by results received from repeated tests
- law: well-tested description of how something in nature works.
- control: standard used for comparison in an experiment.
- independent variable: factor that is changed in a controlled
- dependent variable: factor being measured or observed in a
- constant: variable that stays the same in an experiment.
- graph: diagram that shows the relationship of one variable to
another and that makes it easier to interpret and analyze data.
- technology: application of what has been learned through science.
- sequence: arrangement of things or events in a certain order.
- inference: attempt at an explanation based on observation.
- element: substance that cannot be broken down into simpler
substances and whose atoms are exactly alike.
- electron: tiny, negatively charged particle that is present in all
atoms and that has almost no mass.
- proton: positively charged, heavy particle contained in the nucleus
of all atoms.
- neutron: electrically neutral particle that is present in the nucleus
of all atoms; same mass as proton.
- electron cloud: region surrounding the nucleus of an atom, where
electrons are more likely to be found.
- atomic number: number of protons in the nucleus of an atom of a
- isotope: atoms of the same element that have different numbers of
neutrons in their nuclei.
- mass number: number of neutrons plus the number of protons in the
nucleus of an atom.
- radioactive decay: release of nuclear particles and energy from
unstable atomic nuclei.
- half-life: time needed for one-half the mass of a sample of a
radioactive isotope to decay; can vary from fractions of a second to
billions of years.
- period: horizontal row of elements in the periodic table whose
properties change gradually and predictably.
- group: family of elements with similar physical or chemical
properties that occupies the same column in the periodic table.
- metal: element that is a good conductor of electricity and heat, is
usually a solid at room temperature and is shiny, ductile, and malleable.
- nonmetal: element that is a poor conductor of heat and electricity
and may be a gas or a brittle solid at room temperature.
- metalloid: element that shares some properties with metals and some
- alloy: mixture made of 2 or more elements, one of which is a metal.
- semiconductor: element that doesn't conduct electricity as well as
a metal but does conduct electricity better than a nonmetal.
- electron dot diagram: shows the chemical symbol for an element
surrounded by as many dots as there are electrons in its outer energy level.
- chemical bond: force that hold 2 atoms together.
- ion: atom that is no longer neutral because it has gained or last
- ionic bond: chemical bond that is created when one atom loses one
or more electrons and another atom gains one or more electrons.
- compound: pure substance that contains 2 or more elements.
- covalent bond: chemical bond that forms between atoms when they
- molecule: neutral particle that is formed when atoms share
- formula: combination of chemical symbols that tells what elements
are in molecules and how many atoms of each element are present.
- chemical reaction: energy-requiring process in which chemical
changes occur; formation of new substances that have different properties
than the original substances.
- reactant: substance that exists before a chemical reaction begins;
in a chemical equation, the reactant is listed on the left side of the
- product: substance that is formed by a chemical reaction; in a
chemical equation, the product is placed on the right side of the arrow.
- endothermic reaction: chemical reaction in which energy is
absorbed, such as the reaction that breaks water down into hydrogen and
- exothermic reaction: chemical reaction that releases energy, such
as occurs when propane is burned in a gas grill.
- rate of reaction: measure of how quickly a chemical reaction
occurs, which can be influenced by temperature, particle size, the amount of
activation energy that starts the reaction.
- inhibitor: substance, such as butyl hydroxy toluene (BHT), that
doesn't totally stop a chemical reaction but slows it down.
- catalyst: substance, such as an enzyme, that speeds up a chemical
reaction but is not used up or permanently changed.
- speed: rate of change of an object's position.
- displacement: measures the change in position of an object, using
the starting point and ending point and noting the direction.
- velocity: rate of change of displacement; both speed and direction.
- acceleration: rate of change of velocity; act in the direction of
motion, at an angle, or opposite to the direction of motion.
- mass: quantity of matter in an object and a measure of the object's
inertia; unit is the kilogram.
- inertia: measures an object's tendency to remain at rest or to stay
in constant motion.
- momentum: product of mass and velocity; quantity of motion for an
- law of conservation of momentum: if not outside forces act on a
group of objects, the momentum of the group will not change.
- energy: ability to cause change; cannot be destroyed or created,
only transferred from one form to another.
- kinetic energy: energy an object has due to its motion; depends on
the object's mass and velocity.
- law of conservation of energy: energy cannot be destroyed or
created but it is only transformed from one form to another.
- gravitational potential energy: energy an object could potentially
gain if it falls, depending on its mass and the height it can fall.
- force: push or a pull exerted on an object.
- net force: sum of the forces acting on an object.
- balanced forces: 2 or more forces acting on an object that cancel
each other out and do not cause a change in the object's motion.
- unbalanced forces: 2 or more unequal forces acting on an object that
cause the object to accelerate.
- Newton's first law of motion: an object at rest or moving at a
constant speed in a straight path continues to do so until a net force acts
- friction: rubbing force that acts against motion between 2 touching
- Newton's second law of motion: an object acted upon by a net force
will accelerate in the direction of this force according to the following
equation a-fnet/m where a is the acceleration, fnet is
the net force, and m is the mass.
- normal force: outward force a surface supplies to support an
- Newton's third law of motion: forces always act in equal but
- fault: surface along which rocks break and move.
- earthquake: vibrations caused by breaking rocks along faults; most
result form plates moving over, under, and past each other.
- normal fault: break in rock due to tension forces, where rock above
the fault surface moves downward in relation to rock below the fault
- reverse fault: break in rock due to compression forces, where rocks
above the fault surface move upward and over the rocks below the fault
- strike-slip fault: break in rock due to shearing forces, where
rocks on either side of the fault surface move past each other with little
upward or downward movement.
- seismic wave: energy waves that are produced at and travel outward
from the earthquake focus.
- focus: in an earthquake, the point beneath Earth's surface where
energy release occurs.
- primary wave: wave that travels outward from an earthquake's focus
and cause particles in rocks to move back and forth in the same direction
the wave is moving.
- secondary wave: wave that travels outward from an earthquake's
focus and move through Earth by causing particles in rocks to vibrate at
right angles to the direction of the wave.
- epicenter: point on Earth's surface directly above an earthquake's
- surface waves: waves of energy that reach Earth's surface during an
earthquake, travel outward from the epicenter, and move rock particles up
and down and side to side.
- inner core: very dense, solid center of Earth that is made mostly
of iron with smaller amounts of oxygen, silicon, sulfur, or nickel.
- outer core: liquid core that surrounds Earth's solid inner core and
that is made mostly of iron.
- mantle: largest layer inside Earth, lying directly above the outer
core and that is made mostly of silicon, oxygen, magnesium, and iron.
- crust: Earth's outermost layer, which varies in thickness from
about 5 km to 60 km and is separated from the mantle by the Moho
- seismologist: scientist who studies earthquakes and seismic waves.
- seismograph: device used by seismologists to record primary,
secondary, and surface waves from earthquakes.
- magnitude: measure of the energy released by an earthquake.
- tsunami: powerful seismic sea wave that can travel thousands of kilometers
in all directions and that begins over an earthquake focus.
- volcano: opening in Earth's surface that often forms a mountain
when layers of lava and volcanic ash erupt an build up; occurs where Earth's
plates are moving apart or together and at hot spots.
- vent: opening on Earth's surface where magma is forced up and flows
out as lava.
- crater: steep-walled depression around a volcano's vent.
- hot spot: location in the mantle that is hotter than other areas
and that melts rock, which is forced up toward the crust as magma.
- shield volcano: broad volcano with gently sloping sides formed when
hot, fluid lava flows from one or more vents.
- tephra: bits of rock or solidified lava dropped from the air during
an explosive volcanic eruption.
- cinder cone: steep-sided volcano made of loosely packed tephra.
- composite volcano: volcano formed by alternating layers of
tephra and lava and that is found mostly where Earth's plates come
- batholiths: largest intrusive igneous rock bodies that form when
magma cools underground before reaching Earth's surface.
- dike: intrusive igneous rock body formed when magma is squeezed
into a vertical crack that cuts across rock layers and hardens.
- sill: intrusive igneous rock body that forms when magma is squeezed
into a horizontal crack between rock layers and hardens.
- volcanic neck: solid, igneous core of a volcano left behind when a
volcano stops erupting and the softer cone erodes away.
- calderas: large openings formed when the top of a volcano
- continental drift: hypothesis proposed by Alfred Wegener that
states that continents have moved slowly to their current location on Earth.
- Pangaea: single large land-mass made up of all the continents connected
together that broke apart about 200 million years ago.
- seafloor spreading: magma from below Earth's crust is force upward
toward the surface at a midocean ridge, flows from the cracks as the
seafloor spreads apart and becomes solid as it cools, forming new seafloor.
- plate tectonics: Earth's crust and upper mantle are broken into
sections that move around on a plasticlike layer of the mantle.
- plate: section of Earth's lithosphere that is composed of oceanic
crust, continental crust, and rigid upper mantle and that moves around on a
plasticlike layer of the mantle.
- lithosphere: rigid, outer-most layer of Earth that is about 100 km
thick, and is composed of the crust and part of the upper mantle.
- asthenosphere: plasticlike layer below the lithosphere.
- convection current: cycle of heating, rising, cooling, and sinking
that is thought to be the force behind plate tectonics.
- fossil: remains or traces of once-living organism preserved in
- petrified remains: fossils that form when some or all of the
original materials that made up the organisms are replaced with minerals.
- carbonaceous film: fossil formed when the remains of a once-living
organism are subjected to heat and pressure, leaving only a thin film of
- mold: fossil formed when an organism is buried, decays and leaves
behind a hollow place in the rock.
- cast: fossil formed when sediments fill a mold and harden into
- index fossil: fossils of species that existed on Earth for only a
short time, were abundant, and were widespread geographically; used by
scientists to determine the age of rock layers.
- principle of superposition: undisturbed layers of rocks, older
rocks lie underneath younger and younger rocks.
- relative dating: method to determine the order of events and
relative age of the rocks by examining the position of rocks in a sequence.
- unconformity: gap in the rock layers due to erosion, nondeposition,
- absolute dating: process that uses the properties of atoms in rocks
and other objects to determine their exact ages, in years.
- radioactive decay: release of nuclear particles and energy from
unstable atomic nuclei.
- half-life: time needed for one-half the mass of a sample of a radioactive
isotope to decay; varies from fractions of a second to billions of years.
- radiometric dating: process to determine the absolute ages of rocks
by measuring the amounts of parent and daughter materials in a rock and by
knowing the half-life of the parent.
- uniformitarianism: Earth processes happening today are similar to
those that happened in the past.
- species: group of similar organisms that can successfully reproduce
among themselves in their natural environment.
- evolution: changes in the inherited features of a species over
time; can occur slowly (gradualism) or rapidly (punctuated equilibrium).
- natural selection: Darwin's theory of evolution that
organisms with traits best suited to their environments are more likely to
survive and reproduce.
- variation: an inherited trait that makes an individual different
from other members of the same species; can be beneficial, harmful, or
neutral in a population.
- gradualism: model of evolution that shows a slow change of some
species to another, new species through continued mutations and variations
- punctuated equilibrium: model of evolution that shows the rapid
change of a species caused by the mutation of just a few genes, resulting in
the appearance of a new species.
- sedimentary rock: rock formed by compaction and cementation of
sediments or when minerals precipitate out of solutions or are left behind
when a solution evaporates; rock type formed from particles of preexisting
rocks contains the most fossils.
- radioactive element: element that gives off radiation due to an unstable
- homologous: body structures that are similar in origin and show
that 2 or more species may share common ancestors.
- vestigial structure: body structure with no obvious use, which may
once have functioned in an ancestor.
- embryology: study of development in organisms.
- primates: group of mammals that includes monkeys, apes, and humans,
and that shares several characteristics, such as opposable thumbs and
- hominids: humanlike primates that walked upright on 2 feet and ate
both meat and vegetables.
- Homo sapiens: human species thought to have evolved
about 400,000 years ago.
- geologic time scale: record of events in Earth's history based on
major evolutionary changes and geologic events; major subdivisions are eras,
periods, and epochs.
- era: major subdivision of the geologic time scale based on
differences n life-forms.
- period: next-smaller division of the geologic time scale after the
- epoch: division of geologic time smaller than a period.
- trilobite: organism that lived hundreds of millions of years ago
and is considered an index fossil of the Paleozoic era.
- Precambrian time: longest geologic time unit in Earth's history;
poor fossil record.
- cyanobacteria: one of the earliest life-forms on Earth; evolved
during Precambrian time.
- Paleozoic era: geologic era marked by the first appearance of
life-forms with hard parts.
- amphibian: animals that live on land and breathe air but return to
water to reproduce.
- reptile: egg-laying, scaly-skinned animals that do not need to
return to water to reproduce and probably evolved from the same ancestor as
- Mesozoic era: geologic era in which Pangaea broke up, the
present-day continents were formed, and whose dominant land life-forms were
reptiles and gymnosperms.
- gastrolith: stones swallowed by dinosaurs and by modern birds to
help with digestion.
- Cenozoic era: geologic era in which we live; began with the
extinction of dinosaurs and many other life-forms.
- organic compound: compound that contains carbon.
- hydrocarbon: compound that contains only carbon and hydrogen
atoms--for example methane, CH4, and ethane, C2H6.
- saturated hydrocarbon: hydrocarbon with only single bonds--for
example propane, C3H8, and butane, C4H10.
- unsaturated hydrocarbon: hydrocarbon that has one or more double or
triple bonds--for example ethylene, C2H4, and propylene, C3H6
- isomer: compound with the same chemical formula but different
structures and different chemical and physical properties.
- hydroxyl group: consists of one oxygen atom and one hydrogen atom
joined together by a covalent bond; formula is -OH; when substituted for
hydrogen in a hydrocarbon, forms an alcohol.
- carboxyl group: consists of one carbon atom, 2 oxygen atoms, and
one hydrogen atom; formula is -COOH; when substituted for hydrogen in a
hydrocarbon, forms a carboxylic acid.
- amino group: consists of a nitrogen atom joined by covalent bonds
to 2 hydrogen atoms; formula is -NH2; when substituted for hydrogen in a
hydrocarbon, forms an amine.
- amino acid: building block of proteins; contains both an amino
group and a carboxyl group substituted on the same carbon atom.
- polymer: large natural or synthetic molecule made of many small
organic molecules that link together to form a long chain.
- protein: polymer made of individual amino acids linked together in
a chain; catalyzes many cell reactions and provides the structural material
for many parts of the body.
- carbohydrate: energy-supplying organic compounds that are broken
down into simple sugars in the body; contain only carbon, hydrogen, and
- lipid: energy-supplying and energy-storing organic compounds composed
of 3 long-chain carboxylic acids bonded to glycerol; commonly called
fats and oils and can be saturated or unsaturated.
- stomata: openings on leaf surfaces o leaflike structures through
which gases like carbon dioxide and water vapor may enter and leave a plant.
- transpiration: loss of water vapor through the stomata of a leaf.
- photosynthesis: food-making process that takes place in the chloroplasts
of plant cells, where carbon dioxide from the air, water in the soil, and
light energy react to form glucose and oxygen.
- respiration: series of chemical reactions by which all living cells
break down food to release energy.
- tropism: response of a plant to an outside stimulus such as gravity
- auxin: type of plant hormone that can cause plants to show positive
- photoperiodism: response of a plant to the number of hours of
daylight and darkness it receives each day.
- long-day plant: plant that needs less than 10-12 hours of darkness
to begin the flowering process.
- short-day plant: plant that needs 12 or more hours of darkness to
begin the flowering process.
- day-neutral plant: plant that does not have a specific photoperiod
and whose flowering process can begin over a wide range of hours of
- gametophytes stage: plant life cycle stage in which all plant
structures are made of cells with a haploid number (n) of
- sporophyte stage: plant life cycle stage in which all plant
structures are made of cells with a diploid number (2n) of
- alternation of generations: occurs when a plant's life cycle
alternates between a sex-cell-producing stage and a spore-producing stage.
- frond: leaf of a fern that grows from a rhizome.
- rhizome: underground stem of a fern, from which fronds and roots
- sori: spore-producing structures on the undersides of fern fronds.
- prothallus: fern gametophyte, which can make its own food, absorb water
and nutrients, and has both male and female reproductive structures.
- ovule: in a seed plant, the structure that contains an egg cell,
food0storage tissue, and a sticky fluid.
- pollen grain: produced by the male reproductive organs of seed
plants; 2 sperm develop in each pollen grain.
- stamen: male reproductive organ inside the flower of an angiosperm;
consists of a filament and an anther.
- pistil: female reproductive organ inside the flower of an
angiosperm; consists of a stick stigma, a style, and an ovary.
- ovary: in angiosperms, the swollen base of the pistil where ovules
- pollination: transfer of pollen grains from the stamen to the
- biosphere: part of Earth that supports organisms, is the highest
level of biological organization, and is made up of all Earth's ecosystem.
- ecology: study of the interactions that take place among organisms
and between organisms and the physical features of the environment.
- abiotic factor: all the nonliving, physical features of the
environment, including light, soil, water, and temperature, that help
determine which species can survive in an area.
- biotic factor: living or once-living organisms in the environment.
- population: all the individuals of one species that live in the
same area at the same time and compete with each other for food, water,
mates, and space.
- community: consists of groups of populations that interact with
each other in a given area and depend on each other for food, shelter, and
for other needs.
- ecosystem: consists of a biotic community and the abiotic factors
that affect it.
- population density: size of a population that occupies an area of
- limiting factor: any biotic or abiotic factor that restricts the
number of individuals in a population.
- carrying capacity: largest number of individuals an environment can
support and maintain over a long period of time.
- symbiosis: any close relationship between 2 or more different
- habitat: physical location where an organism lives.
- niche: role of an organism in the ecosystem, including what it
eats, how it interacts with other organisms, and hot it gets food.
- food chain: model that describes the feeding relationships in a
community, usually has 3 or 4 links, and shows how energy in the form of
food passes from one organism to another.
- food web: model used to describe a series of overlapping food
chains and that shows the many organisms that feed on more than one level in
- ecological pyramid: model used to describe the transfer of energy
from the producers of an ecosystem through successive levels of organisms in
the food chain.
- water cycle: constant journey of water molecules on Earth as they
rise into the atmosphere, fall to land or the ocean as rain, or snow, and
flow into rivers and oceans through the processes of evaporation,
condensation, and precipitation.
- nitrogen cycle: transfer of nitrogen from the atmosphere to plants
and back to the atmosphere or directly into plants again.
- ecological succession: process of gradual change from one community
of organisms to another.
- primary succession: ecological succession that begins in a place
that does not have soil.
- pioneer community: first community of organisms to move into a new environment.
- secondary succession: ecological succession that begins in a place
that already has soil and was once the home of living organisms.
- climax community: community that has reached the final stage of
- biome: large geographic areas with similar climates and ecosystems;
6 most common are tundra, taiga, temperate forest, tropical rain forest,
grassland, and desert.
- tundra: cold, dry ,treeless biome located at latitudes surrounding the
north pole and that has winters 6 to 9 months long.
- taiga: cold region of cone-bearing evergreen trees that lies just
below the tundra and is the world's largest terrestrial biome.
- temperate deciduous forest: biome that lies at latitudes below
about 50 degrees in both the northern and southern hemispheres, usually has
4 distinct seasons, and supports a wide variety of plants and animals.
- tropical rain forest: hot, wet, equatorial biome that contains the
largest number of species.
- grassland: temperate and tropical regions that receive between 25
cm and 75 cm of precipitation each year ad are dominated by climax
communities of grasses.
- desert: driest biome on Earth; receives less than 25 cm of rain
each year and supports little plant life.
- plankton: microscopic algae, plants and other organisms that float
in warm, sunlit waters near the surface of freshwater lakes and ponds.
- estuary: area where a river meets the ocean that contains a mixture
of freshwater and salt water and serves as nursery for many species of ocean
- intertidal zone: portion of the shoreline that is covered with
water at high tide and exposed to the air at low tide.
- natural resource: material found in nature that is useful or
necessary for living organisms.
- renewable resource: natural resource, such as water, that is
recycled or replaced by ongoing natural processes.
- nonrenewable resource: natural resource, such as petroleum,
that is available in limited amounts and cannot be replace or is only
- fossil fuel: nonrenewable energy source, such as natural gas, that
formed from the bodies of organisms that died hundreds of millions of years
- photovoltaic (PV) cell: device made of silicon that turns sunlight
directly into electric current.
- hydroelectric power: electricity produced by the energy of flowing
- geothermal energy: heat energy from below the surface of Earth.
- nuclear energy: energy produced when the nuclei of uranium atoms
split apart in a nuclear fission reaction.
- soil depletion: removal of soil nutrients from land used for
agriculture due to the replacement of native plants with crops that do not
decay and replenish the soil.
- erosion: wearing away of soil by wind and water.
- soil management: use of plowing methods to prevent or reduce soil
depletion and erosion.
- extinction: dying out of an entire species either naturally or
through the actions of humans.
- endangered species: species that is in danger of becoming extinct
unless action is taken to protect it.
- recycling: process that reduces the use of natural resources
by reusing an item after it has been changed or reprocessed.
- pollutant: any substance that contaminates the environment and
- smog: air pollution that forms when sunlight reacts with pollutant
chemicals produced by burning fossil fuels.
- acid rain: rain or snow with a pH below 5.6; results from the
mixture of water vapor and air pollutants in the atmosphere.
- ozone depletion: thinning of Earth's protective ozone layer,
primarily from chlorofluorocarbons reacting with and destroying ozone
- greenhouse effect: warming of Earth due to a blanket of gases in
the atmosphere that prevents heat from radiating back into space.
- global warming: increase in the average yearly temperature of
- hazardous waste: waste materials, such as pesticides and nuclear
waste, that are harmful to human health or poisonous to living organisms and
that must be properly disposed of.
- groundwater: water contained in the soil or trapped in underground
pockets formed by nonporous rock; comes from rainfall and runoff that soaks
through the soil.
- electromagnetic spectrum: arrangement of electromagnetic radiation
according to wavelength.
- refracting telescope: optical telescope that uses a double convex
lens to focus light and form an image at the focal point.
- reflecting telescope: optical telescope that uses a mirror to focus
light an produce an image at the focal point.
- observatory: specially designed building, often with a dome-shaped
roof that opens up to admit light; used to house optical telescopes.
- radio telescope: type of telescope that uses a large, curved dish
to collect and record radio waves traveling through space and that can be
used during the day or at night and during bad weather.
- satellite: any object that revolves around another object; can be
natural (Earth's moon) or artificial.
- orbit: curved path of a satellite as it revolves around an abject
- space probe: instrument that travels out into the solar system to
gather information and sends the data back to Earth.
- Project Mercury: 1st step in the US effort to reach the moon, in
which a piloted spacecraft successfully orbited around Earth and returned
- Project Gemini: 2nd stage in the US program to reach the moon, in
which a team of astronauts met and connected with another spacecraft while
- Project Apollo: final stage in the US effort to reach the moon--on
July 20, 1969, Neil Armstrong was the 1st human to set foot on the lunar
- space shuttle: reusable spacecraft that carries astronauts,
satellites, and other materials to and from space.
- space station: large artificial satellite that provides support
systems, living quarters, and equipment so that humans can live and work in
space and conduct research not possible on Earth.
- sphere: round, 3-dimensional object whose surface at all points is
the same distance from its center.
- axis: imaginary line around which Earth spins.
- rotation: spinning of Earth on its axis, which causes day and night
- revolution: yearly orbit of Earth around the sun.
- ellipse: elongated, closed curve that describes Earth's orbit.
- equinox: twice-yearly time when the sun is directly above Earth's
equator and the number of nighttime hours equals the number of daylight
- solstice: point at which the sun reaches its greatest distance
north or south of the equator.
- moon phase: changing appearance of the moon as seen from earth,
which depends on the relative positions of the moon, Earth, and sun.
- new moon: moon phase that occurs when the lighted half of the moon
faces the sun and the dark side faces Earth.
- waxing: occurs shortly after a new moon, when more and more of the
moon's lighted side becomes visible.
- first quarter: moon phase in which one-quarter of the moon's surface
that faces Earth is lit up; occurs about a week after a new moon.
- full moon: moon phase in which all of the moon's surface that faces
Earth is lit up.
- waning: occurs after a full moon, when the amount of the moon's
lighted side that can be seen becomes smaller.
- third quarter: moon phase in which only half of the lighted side of
the moon is visible.
- solar eclipse: eclipse that occurs when the moon moves directly
between the sun and Earth and casts a shadow on part of Earth.
- lunar eclipse: eclipse that occurs when Earth's shadow falls on the
- maria: dark-colored, relatively flat areas of the moon that were
formed when ancient lava filled basins on the moon's surface.
- mascon: concentration of mass on the moon located beneath an impact
- solar system: system of 9 planets that orbit the sun; objects that
orbit the sun.
- inner planet: 4 solid, rocky planets that are closest to the
sun--Mercury, Venus, Earth, and Mars.
- outer planet: 5 planets that are the farthest away from the
sun--Jupiter, Saturn, Uranus, Neptune, and Pluto.
- Mercury: planet closest to the sun; has many craters, low
gravitational pull, and is the 2nd smallest planet in our solar system.
- Venus: 2nd planet from the sun; has a dense atmosphere of carbon
dioxide and sulfuric acid.
- Earth: 3rd planet from the sun; surface temperatures allow water to
exist as a solid, liquid, and gas and atmosphere protects life from the sun's
- Mars: 4th planet from the sun; appears red due to the iron oxide
content in its weathered rocks.
- astronomical unit: average distance from Earth to the sun (150
million km), which is used to measure distances to objects in the solar
- Jupiter: largest planet and 5th planet from the sun; composed
mostly of hydrogen and helium; has continuous storms of high-pressure gas.
- Uranus: large, gaseous planet and 7th planet from the sun; has a
magnetic pole tilted 60 degrees and rotates on an axis nearly parallel to
the plane of its orbit.
- Neptune: large, gaseous planet similar to Uranus; usually the 8th
planet form the sun.
- Pluto: smallest planet and considered the 9th planet from the sun;
has a thin, changing atmosphere and icy-rock
- Saturn: 6th planet from the sun; has a complex ring system made of
hundreds of ringlets.
- Great Red Spot: high-pressure storm generated by huge thunderstorms
in Jupiter's atmosphere.
- comet: mass of dust and rock particles mixed in with frozen water,
ammonia, and methane; consists of a nucleus, a coma, and a tail.
- Oort Cloud: cloud of comets that completely surrounds the solar
system and that is located beyond the orbit of Pluto.
- meteor: meteoroid that burns up in Earth's atmosphere.
- meteorite: meteoroid that does not completely burn up in Earth's
atmosphere and strikes Earth.
- asteroid: piece of rock usually found in the asteroid belt between
the orbits of Mars and Jupiter.
- constellation: group of stars that forms a pattern that looks like
a familiar object, animal, or character.
- absolute magnitude: measure of the amount of light a star actually
- apparent magnitude: measure of the amount of light that is
received on Earth from a star.
- parallax: apparent shift in position of an object when it is viewed
from 2 different positions.
- light-year: distance that light travels in one year (9.5 trillion
km), which is used to measure distances in space.
- photosphere: lowest layer of the sun's atmosphere and the layer
that gives off light.
- chromospheres: layer of the sun's atmosphere above the photosphere
and below the corona.
- corona: largest layer of the sun's atmosphere that extends millions
of miles into space.
- sunspot: dark, relatively cool areas on the surface of the sun.
- binary system: system in which 2 stars orbit each other.
- main sequence: in an H-R diagram, the diagonal band of stars that
runs from hot, bright stars in the upper-left corner of the diagram to cool,
faint stars in the lower-right corner.
- nebula: large cloud of gas and dust that can fragment into smaller
pieces, each of which will collapse and form stars.
- giant: stage in a star's life cycle where hydrogen in the cores is
used up, the core contracts, and temperatures inside the star increase,
causing the outer layers of the star to expand.
- white dwarf: late stage in a star's life cycle where its core uses
up its supply of helium, it contracts, and its outer layers escape into
space, leaving behind the hot dense core.
- supergiant: late stage in the life cycle of a massive star where
the core reaches very high temperatures, heavy elements form by fusion, and
the star expands.
- neutron star: collapsed core of a supernova that shrinks to about
10km to 15 km in diameter and has only neutrons in the dense core.
- black hole: remnant of a star that is so dense that nothing can
escape its gravity.
- galaxy: large group of stars, gas, and dust held together by
- big bang theory: approximately 15 billion years ago, the universe
began expanding out of an enormous explosion.