NASA - National Aeronautics and Space Administration

a | b | c | d | e | f | g | h | i | j | k | l | m | n | o | p | q | r | s | t | u | v | w | x | y | z

A

abiotic - Abiotic describes conditions and factors that are the nonliving elements of an ecosystem. Examples of abiotic factors include climate, air currents, temperature, moisture, light, and soil type. top

abort motor - The abort motor generates 1,800,000 Newtons (400,000 pounds) of thrust in a fraction of a second to rapidly move the crew to safety during a launch pad or in-flight emergency. top

absorb - Absorb means to take in. Light energy that is absorbed is not given off, it is taken in by the object that absorbs the light. As a result, the object may become warmer. top

absorption spectrum - An absorption spectrum is a spectrum, broken by a specific pattern of dark lines or bands, observed when light passes through a gas. The absorption pattern is unique and can be used to identify the gas. top

acceleration - Acceleration is any change in speed or velocity (when an object speeds up, slows down, or changes direction). Acceleration can be described as positive or negative (e.g., speeding up is positive acceleration, slowing down is negative acceleration). top

aerodynamic heating - Aerodynamic heating is the heating of a solid body produced as air or other fluid passes over the body. top

aerodynamics - Aerodynamics is the study of how efficiently air flows around an object. top

airfoil - An airfoil is a surface, such as a wing or propeller, designed to aid in lifting and controlling an aircraft by means of air currents. top

amplitude - Amplitude is a measure of the height of a sound wave which determines the sound's volume. top

anisotropic - Anisotropic materials have a crystalline structure where the arrangement of atoms along one axis is different than that of another axis. Optically anisotropic materials rotate polarized light as it passes through them. top

anthrosphere - The anthrosphere is the part of the environment that is created or modified by humans for use in human activities and human habitats. top

arteries - Arteries are blood vessels that carry blood away from the heart. top

artificial satellite - An artificial satellite is a manufactured object that continuously orbits Earth or some other body in space. top

astronaut - An astronaut is a person who is trained to travel into space. top

astronomers - An astronomer is a person who studies objects in space. top

atmosphere - The atmosphere is the envelope of gases surrounding Earth. top

atom - Atoms are the smallest part of an element that maintains the chemical properties of that element. top

attitude control motor - The attitude control motor helps to stabilize and reorient the Orion crew module before the crew module is released from the abort system to begin its controlled descent. top

attitude - Attitude describes the position of a spacecraft relative to the direction of motion. top

B

ballast - Material inside a vehicle that give it additional mass for stability or other purposes. This material gives the vehicle more weight, a force pulling down toward the center of the Earth. Ballast is sometimes designed to be disposable. top

Bernoulli's Principle - Bernoulli's principle states that as the velocity of a fluid (such as air) increases, the pressure exerted by that fluid decreases. top

biome - A biome is a major biotic community characterized by distinct climate and dominant forms of flora and fauna. top

biosphere - The biosphere is the region of the Earth's surface and atmosphere where living organisms exist. top

Biosphere 2 - Biosphere 2 is a model of Earth's biosphere located north of Tucson, AZ. top

birefringence - Birefringence is a process where light of different polarizations travels at different speeds in different directions through a transparent medium. Birefringence is also called double refraction. top

black hole - A black hole is a region of space with gravitational force so strong that nothing can escape from it. top

blood vessels - Blood vessels are tubes that carry blood. They include arteries, veins, and the capillaries that connect them. top

buoyancy - Buoyancy is an upward force on an object in a fluid, e.g., when you float in a pool or the ocean or a balloon floats in air top

C

camber - Camber is the difference between the top and bottom curves of an airfoil. Airplane wings tend to have a longer curve on the upper than the lower wing surfaces (although the opposite is true of supersonic jets). top

capillaries - Capillaries are the thinnest blood vessels. Nutrients and gases can pass through capillary walls. Capillaries connect veins and arteries. top

carbon dioxide - Carbon dioxide is a colorless, odorless, non-poisonous gas that is a normal part of Earth's atmosphere. Carbon dioxide is a product of fossil fuel combustion. top

chlorophyll - Chlorophyll is a green chemical in plant cells that allows plants to use light energy to make food. top

clay - Clay is soil with very small particles. top

climate - Climate is the long-term weather pattern of an area, including temperature, precipitation, and wind. top

cloud - A cloud is a large collection of very tiny droplets of water or ice crystals in the atmosphere. top

Clouds and the Earth's Radiant Energy System, or CERES - CERES is a sensor flown on satellites to collect data about Earth's systems. top

coma - A coma is the cloud that forms around a comet's nucleus. This cloud is made when a comet travels near the sun. top

comet - A comet is a small object found in the solar system. It is made mostly of ice and dust. top

composite materials - Composite materials are two or more different materials that are combined together. The combined materials do not lose their individual properties. The properties of the product are a combination of the properties of each material. top

compression - Compression is the process of molecules being pressed closer together. top

compression wave - A compression wave is a wave that is propagated by the compression of molecules in a substance. top

condensation - Condensation is the process of a gas changing to a liquid. top

conduction - Conduction is the transfer of heat between two solid objects that are touching. top

conductors - Conductors are materials that easily transfer heat or electricity. top

constellation - The definition of constellation you may be familiar with is a group of stars that can be connected together to form a pattern such as the “Big Dipper.” NASA’s mission which includes building a new vehicle, the Orion, capable of going to the Moon for lunar exploration and research, is called the Constellation Program. top

constraint - Any limit or restriction given for the design process is called a constraint. top

contracts - When the heart contracts, or gets smaller, the heart muscle is squeezing a larger space within the heart into a smaller space. top

controlled descent - A controlled descent is a landing where the speed and direction of the fall is modified. top

convection - Convection is the transfer of heat between flowing gases or liquids. top

coordinate system - A coordinate system is a grid placed on a map to help quickly locate specific locations. top

cosmologist - A cosmologist is a scientist or astronomer who studies large scale structures and dynamics of the universe, including the origins of the universe. top

covalent bond - A covalent bond is a chemical bond formed between two atoms by sharing electrons between the atoms. top

Crew Exploration Vehicle (CEV) – The Crew Exploration Vehicle (CEV) is America’s new spacecraft for human space travel. The CEV will carry four crew members to the Moon. It can carry six crew members on missions to the International Space Station or to low-Earth orbit to transfer to a Mars-bound spacecraft. top

criteria - Criteria are rules guiding the design process, such as size, type of material, or dollar limit to build the model. top

cross-polarizers - Cross-polarizers are created when two pieces of polarizing film are placed at 90 angles to each other. top

cryosphere - The cryosphere is the part of Earth's system that includes water in its frozen state. Earth's cryosphere includes snow, sea ice, lake ice, glaciers, permafrost, ice caps, and ice sheets. top

crystal lattice - A crystal lattice is the structure of an ionic solid in which orderly top

D

dark matter - Dark matter is the name given to the amount of mass whose existence is deduced from the analysis of galaxy rotation curves but which until now has escaped all detection. There are many theories about dark matter, but the subject is still a mystery. top

decibel - The decibel (dB) is a unit of sound intensity top

decompose - To decompose is to break down. The process of decomposing is the breaking down of dead plants and animals into tiny pieces. When these pieces mix with dirt they form soil. top

density - The density (d) of a material or object is a measure of how tightly the matter within it is packed together, and is given by the ratio of its mass (m) to its volume (V), or d = m/V. It is typically expressed in kilograms per cubic meter (kg/m³) or grams per cubic centimeter (g/cm³) or grams per milliliter (g/mL). top

deposit - To deposit is to drop off. Wind and water often carry sand and mud particles from one place and later deposit them somewhere else. What they drop off is called a deposit (so deposit is both a verb and a noun). top

design process - The design process is a series of steps in designing and refining/improving something. Steps of the Design Process 1. Identify the problem 2. Identify criteria and constraints 3. Brainstorm possible solutions 4. Generate ideas 5. Explore possibilities 6. Select a design 7. Build a model or prototype 8. Refine the design, repeating steps 1-8 top

diffraction grating - A diffraction grating is a surface with many closely spaced parallel grooves or splits in it which splits and diffracts light to produce the light's spectrum. top

dirt - Dirt is made of small particles formed from the breakdown of rocks. top

drag - Drag is the resistance on an object to movement through a fluid. It is a force that slows an object down. For example, swimmers and submarines experience drag as they move through water and birds and aircraft experience drag as they move through air. top

drop test - An experiment that measures speed, velocity or acceleration of a falling object, or the results of a fall or the impact of the fall, is called a drop test. top

E

Earth Orbiting System - The Earth Orbiting System, or EOS, is a series of satellites that orbit Earth and collect various types of data. top

Earth system - The Earth system is a unified system comprised of six spheres: the anthrosphere, atmosphere, biosphere, cryosphere, geosphere, and hydrosphere. top

electromagnetic radiation - Electromagnetic radiation is energy radiated in the form of waves. It consists of electric and magnetic fields traveling at the speed of light. top

electromagnetic spectrum - The electromagnetic spectrum is the entire range of visible and invisible energy waves organized according to wavelengths. Visible light is a small part of the electromagnetic spectrum, which includes radio waves, ultraviolet waves, infrared waves, and microwaves. The shorter wavelengths have the highest energy. top

emission spectrum - An emission spectrum is a spectrum of bright lines or bands of light of specific wavelength which are emitted when a gaseous element is exposed to high energy. Each element has its own unique pattern of bands. top

emit - To emit is to give off. LEDs give off, or emit, light. Colored LEDs emit very specific wavelengths of light. top

energy - (see also thermal energy) Energy is the ability to do work, and there are several different forms of energy (e.g., kinetic, potential, thermal, sound, light, chemical, etc.). While energy may be transformed from one form to another, the total energy remains the same within a closed system. top

engineers - Engineers use math and science to design new tools and devices to solve practical problems. top

evaporation - Evaporation is the process of changing from a liquid to gas. top

expands - When the heart expands, or gets larger, the heart muscles stretch and the spaces within the heart spread out. top

extinct - An extinct animal or plant is one that has died out. top

F

Fermi Gamma-ray Space Telescope - Fermi is a space telescope that consists of two parts: the Large Area Telescope, or LAT, and the Fermi Burst Monitor. The LAT has a wide field of view and can detect gamma rays. The Fermi Burst Monitor observes gamma ray bursts which are sudden, brief flashes of gamma radiation that occur about once a day. top

filament - A filament is a small thin wire inside an incandescent light bulb that is heated until it glows. top

fluid shift - While in space, fluids in the body move from the lower part of the body toward the head. This movement is fluid shift. top

fluid - A fluid is a substance that will flow. When a substance flows, the particles in the fluid can move past one another. Both liquids and gases are fluids. top

fluorescent light - A fluorescent light uses an electric current to heat gas particles inside a specially coated glass tube. When the particles hit the sides of the tube, a glowing light is produced. top

force - A force is whatever can cause an object with mass to accelerate (change its direction or speed). Force may be expressed with both magnitude (speed or velocity) and direction making it a vector quantity. top

forced convection - Forced convection occurs when a pump or other mechanism moves a heated fluid. top

fossil fuel - Fossil fuel is a general term for crude oil, coal, natural gas, or heavy oils. These fuels are created by exposure to heat and pressure in the earth's crust over hundreds of millions of years. top

freezing point - The freezing point of a liquid is the temperature at which the liquid changes state from a liquid to a solid. top

frequency (v) - Frequency is the number of waves that pass a fixed point in a given period of time. The frequency of electromagnetic radiation is measured in hertz (Hz) which is defined as the number of waves per second. top

G

g - The force of Earth’s gravity. top

gantry - NASA’s gantry is a large apparatus in Hampton, Virginia that was built to test Apollo space capsules. Now it helps researchers test the Orion space capsule (see Figure 3). top

geosphere - The geosphere is the solid portion of Earth and the processes that shape Earth's surface. top

geosynchronous orbit - A geosynchronous orbit is a satellite orbit at approximately 35,800 kilometers above the Equator in which objects travel at the same speed as Earth. Objects in this orbit remain stationary in reference to Earth. top

glacial advance - Glacial advance is an increase in the thickness and area of a glacier. This term also describes the time period it takes for the increase in glacial thickness to occur. top

glacial retreat - Glacial retreat occurs when backward melting at the front of a glacier takes place at a rate exceeding forward motion. top

global climate change - Global climate change is the long-term fluctuations in temperature, precipitation, wind, and all other aspects of Earth's climate. top

gravity - Gravity is a force between objects based on their masses and the distance between the objects. The force of gravity on the moon is less than the force of gravity on Earth because the moon has only 1/6 the mass of Earth. Earth's gravity is described as 1g. top

greenhouse gases - Greenhouse gases are gases that contribute to the warming of the Earth's atmosphere by reflecting solar radiation from Earth's surface. Carbon dioxide, ozone, and water vapor are examples of greenhouse gases. top

ground truth - Ground truthing is a validation process where a person on the ground (or sometimes in an airplane) makes a measurement of the same phenomenon a satellite is measuring, at the same time the satellite is measuring it. The two answers are compared to evaluate how well the satellite instrument is performing. The actual measurements taken on Earth are called "ground truth." top

H

heat - Heat is the amount of thermal energy absorbed, released, or transferred by a material. This is typically expressed as q, and is measured in joules (J). top

HIAD - (Hypersonic Inflatable Aerodynamic Decelerators) HIADs are inflatable heat shield structures made up of incredibly strong, yet flexible fabric designed to maintain shape and withstand head during atmospheric reentry. top

highlands - Highlands are mountainous regions of land. top

hill - A hill is raised above the surrounding land, but is smaller than a mountain. top

Hubble Space Telescope, HST - The Hubble Space Telescope is a large telescope that orbits Earth. It is named after astronomer Edwin P. Hubble (1889-1953). top

humus - Humus is part of the soil that is made up of decayed organic materials. top

hydrosphere - The hydrosphere is the part of Earth that is composed of water. top

I

ice age - An ice age is a cycle cold period marked by periods of glacial advance with episodes of glacial retreat. top

ice core - Ice cores are cylinders of ice obtained by drilling into a glacier. top

ice sheet - An ice sheet is the layer of ice covering a large land mass, notably Antarctica and Greenland. Ice sheets form from the compression of snow as new snow builds on top of it. top

incandescent light - An incandescent light produces light when a metal wire inside a glass bulb is heated and gets hot enough to glow. The glass bulb contains an inert gas that does not react with the filament top

inclination - Inclination is the angle between a reference plane and another plane or axis of direction. For an artificial satellite, the reference plane is the Equator. The inclination of a satellite's orbit is the angle that the orbit crosses the Equator. If a satellite has a 0° inclination then it would be orbiting over the Equator. If a satellite has a 90° inclination, then its orbit is perpendicular to the Equator and it would pass over the poles. top

inertia - Inertia is the tendency of an object to continue doing what it is doing, either moving or resting, unless acted on by an outside force. The inertia of an object is related to its mass (the greater the mass, the greater the inertia). top

infrared - Infrared wavelengths are longer than visible light and give off heat. top

infrared thermometer - An infrared thermometer is a tool that measures the heat being given off by an object. top

insulator - An insulator is a material or substance that does not conduct heat, sound, or electricity easily. top

intensity - Sound intensity is the amount of energy transferred by a sound wave per unit time. top

ionic - Ionic compounds are compounds in which the atoms are held together by ionic bonds. An ionic bond is a chemical bond in which one atom loses one or more electrons to form a positive ion and another atom gains one or more electrons to form a negative ion. The force of attraction between the positive and negative ions forms the bond. top

isotropic - Isotropic materials have a crystalline structure where atoms are arranged in the same way along each axis. top

J

joule (J) - The joule is a unit of energy. One joule is the energy expended when 1 Newton of force is applied to move an object a distance of 1 meter. top

K

Kuiper Belt - The Kuiper Belt is the region beyond the orbit of planet Neptune, similar to the asteroid belt, consisting of the remnants from our Solar System's formation. top

L

latent heat - Latent heat is heat energy that is released or absorbed by a substance when it changes from one phase to another. top

latitude - Latitude is the number of degrees north or south of the Equator. The Equator is 0°N or S, and the North and South Poles are 90° N and 90° S respectively. To visualize this think of Earth as a circle divided into 360°. top

launch abort system, or LAS - The launch abort system offers a safe, reliable method of moving the entire crew out of danger in the event of an emergency on the launch pad or during the climb to Earth orbit. top

lift - Lift is an upward force resulting from pressure differences (e.g. different pressures on the top and bottom of a bird's or an aircraft's wing moving through a fluid) due to the air above the wing traveling faster than the air below the wing, because the upper surface is longer than the lower surface. top

light bank - A light bank is a group of lights that are connected. A Solid State Lighting Module, or SSLM, is a light bank made up of rows of light-emitting diodes. top

loam - Loam is soil made up of a mixture of sand, silt, and clay. top

longitude - Longitude is the number of degrees east or west of the Prime Meridian, the 0° E or W line going through Greenwich, England and the North and South Poles. The Prime Meridian divides the globe into eastern and western hemispheres. It runs between the Poles through the Pacific Ocean on the side of the globe opposite England. This line is called the International Date Line. Degrees longitude are 0° E or W at the Prime Meridian and 180° E or W at the International Date Line. top

longitudinal wave - A longitudinal wave is a wave whose particles vibrate parallel to the direction the wave is traveling. top

low-Earth orbit – Low-Earth orbit (LEO) is the path in which a spacecraft or satellite moves around the Earth. This path may be between 320 and 800 kilometers (200-500 miles) above the Earth’s surface. top

lowlands - The lowlands are sections of ground lower than the surrounding area. A valley is an example of lowlands. top

Luna - Luna is the official name of Earth's moon. top

luster - Luster is a way a mineral reflects light from its surface. Words like shiny and dull describe the luster of a mineral. top

M

mass - The amount of matter in an object is the object’s mass. Objects are made up of atoms containing varying numbers of protons, neutrons, and electrons which determine their mass. Mass is also described as how hard it is to change the motion of an object. top

magnitude - Magnitude is the size (or amount or quantity) of a measurement or object. top

matter - Matter is often defined as anything that has mass and takes up space (has volume), and it is the generic term for the substance of which all physical objects are composed. Matter can be in several different states, including solids, liquids or gases. top

melting point - The melting point of a solid is the temperature at which the solid changes state from a solid to a liquid. top

microgravity - The condition of microgravity (a small amount of gravity) exists when objects are in free fall, like the space shuttle and other objects orbiting the Earth. The objects would actually fall to the Earth if they weren't moving very quickly in a different direction. top

mixture - A mixture is a physical combination of two or more substances. Each substance in a mixture retains its own physical and chemical properties. top

model - A model represents something else. A model might be a drawing or a 3-D object. Models are smaller than the original object or made out of less expensive materials than the actual object. Many iterations (repetitions or versions) of model are often needed before the actual object (for instance, the Orion spacecraft) can be built. The first version is often a drawing scaled down to fit on a piece of paper. The next may be a series of structures made out of paper, cardboard, plastic, or other readily available materials. top

molecule - A molecule is a group of two or more atoms held together by a covalent bond. top

monomer - A monomer is a small molecule that is linked with large numbers of other small molecules to form a chain or a network (polymer). top

mountain - A mountain is any place on Earth that rises sharply and is well above its surroundings. top

N

net force - The net force is the total of all of the forces acting on an object. These forces are vectors, which means they have direction as well as magnitude. top

neutron star - A neutron star is the type of star formed when a massive star explodes as a supernova, leaving behind an ultra dense core. top

Newtonian fluid - A Newtonian fluid is a fluid that reacts the same way no matter how much stress, or force, is applied to it. top

non-Newtonian fluid - A non-Newtonian fluid is a fluid that changes behavior depending on the amount of stress, or force, applied to it. top

nucleus - The nucleus of the comet is the solid, rocky part of the comet. top

nutrients - Nutrients are substances that an organism (plant or animal) needs in order to survive and grow. top

O

orbit - An orbit is the path of a celestial body or an artificial satellite as it revolves around another body. top

orbital decay - Orbital decay is the reduction in altitude of a satellite's orbit caused by gravity and drag from the atmosphere. top

orbital period - Orbital period is the time it takes a satellite to complete one orbit. top

Orion - NASA's Orion crew exploration vehicle will replace the space shuttle after it is retired. Orion is the flagship of NASA's programs for space exploration beyond low Earth orbit and a key element of NASA's Constellation Program to explore the Moon, Mars and beyond. top

oxygen - Oxygen is a gas found in air that cells need to live (represented by O2). top

P

pH - pH is a measure of the concentration of hydrogen ion (H+) in a substance which determines if a solution is acidic or basic. top

parts per million by volume (ppmv) - Parts per million by volume is the measure of the concentration of a gas within the atmosphere. In this case, it measures the concentration of carbon dioxide in the air. top

permafrost - Permafrost is any soil or rock that is frozen throughout the year. top

phase change - A phase change occurs when matter changes from one state to another. This is any combination of changing from a solid to a liquid to a gas. top

phase - Phase describes the physical state of matter. The four common phases of matter are solid, liquid, gas, and plasma. top

photon - A photon is a quantum, or discrete amount, of light energy. Photons have no mass and behave like both a particle and a wave. top

physical map - A physical map shows the location of major landforms such as mountains, plains, and deserts. It also shows country borders and major cities. top

plains - Plains are large, flat, level ground. Plains are often covered with low grasses and have very few or no trees. top

Planck's constant (h) - Planck's constant is a physical constant relating the energy of a photon to its frequency. The value of this constant is approximately 6.626 x 10-34 joule·second. top

polar orbit - A polar orbit is an orbit in which the satellite passes over the North and South Poles on each orbit, and eventually passes over all points on Earth. top

polarized light - Polarized light waves are vibrating in one direction as they pass through or are reflected by certain media. top

political map - A political map shows the location of cities and the borders of countries and states. top

polymer - A polymer is long or large molecule consisting of a chain or network formed by chemically bonding many repeating units, or monomers, together. top

precipitation - Precipitation is water in the atmosphere that falls to Earth as rain, snow, hail, sleet, or freezing rain. top

pressure - Pressure is the force per unit area. Even though you can't feel it, air has pressure. Air molecules move continuously. The more times they bump into each other or a surface, the greater the pressure. Air pressure is increased by: 1. increasing the number of molecules in the same amount of space (volume); 2. increasing the temperature (it makes the air molecules move faster); or 3. decreasing the volume. top

projectile - A projectile is any object that is thrown or otherwise launched. It is affected by Earth's gravity. A projectile may start at a given height and move toward the ground in an arc. Regardless of its path, a projectile will follow these rules: • Projectiles maintain a constant horizontal velocity (in the absence of air resistance). • On Earth, projectiles experience a constant vertical acceleration of 9.8 m/s2 (32 ft/s 2) downward (in the absence of air resistance). top

prototype - A prototype is an original or model on which something is based. top

pulsar - A pulsar is a rotating neutron star which generates regular pulses of radiation. top

pulse rate - A pulse rate is how many times a heart beats in one minute. top

Q

qualitative data - Qualitative data are sets of information that describe attributes. top

quantitative data - Quantitative data are values that can be counted or measured. top

R

R-value - The R-value measures a material's insulating properties. top

radiation - Radiation is the transfer of heat through space. top

rarefaction - Rarefaction is the process of molecules becoming more spread out (as opposed to compression). top

recycled - Used materials that are made into new products are called recycled materials. Recycling reduces the waste of useful materials, and it reduces the need for new materials. Recycling sometimes reduces energy, costs, and pollution. top

reduced gravity - Reduced gravity is less gravity than normally experienced on Earth, or less than 1g. top

reflect - Reflected light is light that hits a surface and bounces off. top

refract - When light is refracted it is bent. Light refracts when it passes from one material to another. top

regolith - A fine dust called regolith covers the moon. Regolith is created when micrometeoroids bombard the moon's surface, breaking up moon rocks. (The vowels are pronounced like those in "LEGO" and "miss.") top

rehydrate - To rehydrate is to put water back into the body that is removed during spaceflight or after exercise on Earth. top

reusable - Objects or materials that can be used again are called reusable. The objects may be used for the same purpose or different purposes. top

relief map - A relief map shows the variation in land heights. The different heights are shown as lines or different colors. top

S

sand - Sand is rock material that has been eroded into small grains. top

saturated solution - A saturated solution contains the maximum amount of solute that can be dissolved in a given amount of solvent at a specified temperature. top

scale factor - Scale factor is the ratio of any two corresponding lengths in two similar geometric figures. top

scale - Scale is the ratio of the length in a drawing, or model, to the length of the real object. If you scale an object, you size or measure it proportionately. top

scientists - Scientists use systematic methods to study the world around them. They use an organized approach to observe and study the world. They ask questions, look for patterns, and try to find general rules for the natural world. top

sediments - Sediments are particles that have been deposited by some natural process, such as blowing wind or moving water. top

self-healing material - Self-healing materials are able to repair damage by closing the gap around a penetrating object. top

silt - Silt is made of particles smaller than sand. top

similar - Geometric shapes are similar if their corresponding sides are proportional and corresponding angles are equal. top

simulation - A simulation is something that substitutes for the real thing. For instance, flight simulators are mockups for pilots to practice so they do not crash real aircraft under different weather and equipment emergencies. A simulation can have many qualities of the authentic experience without all the expenses and dangers. A model simulates - or is a simulation of - a real object or event. top

soil - Soil is a mixture of minerals, weathered rocks, and decayed plant and animal material. top

solar flares - Solar flares are violent eruptions of gas on the sun's surface. top

solar radiation - Solar radiation refers to energy that travels in rays or waves and originates from the sun. top

solar system - The solar system includes the sun, the planets, and other bodies that revolve around the sun including comets. top

solid rocket boosters - Solid rocket boosters use a propellant/fuel in solid form. Two solid rocket boosters enable the shuttle to reach Earth orbit. top

solute - The solute is the dissolved component of a solution. The solute is usually, but not always, present in a smaller amount than the solvent. top

solution - A solution is a mixture in which the components are evenly mixed so that every part of the mixture is the same as any other. top

solvent - The solvent is the component of a solution that dissolves one or more solutes. top

sound - Sound is a form of energy produced and transmitted by vibrating objects. top

sound wave - A sound wave is a series of compressions and rarefactions traveling through a substance. top

specific heat - Different materials require different amounts of heat to produce similar changes in their temperatures. In other words, materials have different specific heat capacities, often called, specific heat. The specific heat capacity of a material is the amount of energy it takes to raise the temperature of 1 gram of the material 1 degree Celsius. Specific heat capacity can be measured in joules per gram per degree Celsius (J/g ˚C). top

spectrometer - A spectrometer is a tool that helps scientists study comets. Spectrometers can be found on satellites, rockets, airplanes, and telescopes. A spectrometer works like our eyes, but it breaks light into colors like a rainbow. top

spectroscope - A spectroscope is an instrument used to produce and observe spectra. top

spectroscopy - spectroscopy refers to the science and practice of using spectrometers and spectroscopes and of analyzing spectra. top

speed of light (c) - The speed of light is the speed of electromagnetic radiation in a perfect vacuum. The speed of light is the same for all frequencies of electromagnetic radiation, 3.0x10 8 m/s. top

speed - Speed is the time it takes an object to travel a certain distance. Speed equals distance divided by time or s = d / t. top

states of matter - States of matter are the distinct forms of matter. Three common states of matter are solid, liquid, and gas. top

sun-synchronous polar orbit - A sun-synchronous polar orbit is a special kind of polar orbit. When traveling in this orbit, a satellite not only travels over the North and South Poles, but it passes over the same part of Earth at roughly the same time each day. Tracking and Data Relay Satellite or TDRS - TDRS is a system of nine geosynchronous communications satellites. They are used to communicate from Earth to orbiting satellites, the space shuttle, and the International Space Station. top

symmetrical - When an object is balanced, or equal on both sides, it has symmetry and is called symmetrical. top

T

tail - The comet's tail forms when the comet travels near the sun. The tail always points away from the sun. top

telescopes - Telescopes are tools that help you see objects that are far away. top

temperature - Temperature is a measure of the average heat or thermal energy of the particles in a substance. top

Terra - Terra is the official name of Earth. top

texture - Texture is the way something feels. For instance, sand feels rough (has a grainy texture) while smaller mud particles have a smoother or slimy texture. top

thermal energy - Thermal energy is the energy of movement of the molecules within a substance. The higher the temperature, the faster the molecules move, thus temperature can be used as a measure of thermal energy. top

thermal protection system - A thermal protection system is a combination of materials used to insulate and reduce the amount of heat transferred to a spacecraft as it enters an atmosphere. top

thrust - Thrust is a force that propels an object. Thrust must be greater than drag for an object to move forward. top

trajectory - Trajectory is the path that an object takes moving through space. top

trend - A trend is a general direction of movement. On a graph, the trend is the overall direction (either increase or decrease) of the values graphed. top

U

ultraviolet - Ultraviolet wavelengths are shorter than visible light. Shorter waves have more energy. Ultraviolet radiation can burn and cause skin cancer. top

V

valley - A valley is a place that is naturally lower than the surrounding land. Valleys are often located between mountains or hills. top

variable - A letter that represents a group of numbers is called a variable. Variables are italicized. That’s how you can tell them apart from units such as grams (g). An example of some variables used in this activity: s = speed, d = distance, t = time or s = d / t . Two variables you use all the time to plot points on a graph are the x and y coordinates [e.g., Plot point (x, y)]. top

vector - A vector is a variable (something that can change/vary) that is composed of both an amount and a direction. An example of a vector is velocity. What makes velocity different than speed is the direction of travel. Wind velocity is a way vectors are used in everyday life. When the weather report states the wind is 40 kilometers per hour (25 miles per hour) out of the west, the wind's velocity, not speed, is what is being reported. top

vector quantity - A vector quantity is any force that has both size and direction. For example, speed becomes a vector once you give it a direction. top

veins - Veins are blood vessels that carry blood back to the heart. top

velocity - The speed and the direction of travel of an object is the object’s velocity. Velocity is similar to speed, but whereas an example of speed would be, “the wind was blowing at 40 miles per hour,” velocity would be expressed as “40 miles per hour from the SE.” Direction becomes important when dealing with navigation of boats, aircraft, wind and water currents, etc. top

visible light - Visible light is the part of the electromagnetic wave that can be seen by the human eye. top

volume - The volume of an object is how much space it occupies, and it is typically expressed in milliliters (mL), cubic centimeters (cm or cc), liters (L) or cubic meters (m3). top

W

water cycle - The water cycle is one part of the Earth system. It involves the movement of water from Earth's surface to the atmosphere and back through the processes of evaporation, condensation, and precipitation. top

wavelength - Wavelength is the distance between two crests or two troughs on a wave. Light is classified by its wavelength. Wavelength is usually measured in meters. top

weather - Weather is the current state of the atmosphere, measured in terms of temperature, pressure, humidity, wind speed and direction, cloudiness and precipitation. top

weathering - Weathering is a process through which rocks or other materials are broken down. Wind, moving water (rivers and waves) and glaciers all cause weathering. top

weight - Weight is the force of gravity on an object. Here on Earth, it means how hard the Earth pulls down on objects. Because the moon is smaller than the Earth, the moon wouldn't pull down on an object as hard and it would weigh a lot less there. However, since the object would still be made up of the same number and type of particles, its mass and density would be the same on the Earth and on the moon. top