air The mixture of gases that forms the earth’s atmosphere.
air pressure The weight of air pressing on the earth; at sea level, about 14.7 pounds per square inch.
angle of repose The greatest angle at which rocks, sand, or other material can remain without sliding.
anvil bone The tiny bone in our middle ear, shaped like an anvil, that conducts sound waves to the stirrup bone.
auditory nerve The nerve leading from the inner ear to the brain that allows us to hear different sounds.
axis An imaginary line through the earth’s poles, around which it rotates; the earth’s axis is tilted 23.5° with respect to the sun.
base plate A rectangular plate on which the orienteering compass housing is mounted, that shows markings including the direction of travel arrow.
boulder A rock larger than 10 inches at its widest part.
capillary action The movement of water inside tiny spaces, even upwards against the force of gravity, caused by the attraction of water molecules to each other and to various other materials.
carbon dioxide A colorless, odorless gas found in the atmosphere and used by plants for photosynthesis.
cardinal direction One of the four main points of a compass – north, east, south, or west.
cirrus Wispy clouds, often in long curling strands, found above 20,000 feet, made of tiny ice crystals rather than water droplets.
cloud A mass of tiny water droplets or ice crystals suspended in the air, that looks white or gray and may produce rain or snow.
cobble A rock larger than 2.5 inches but less than 10 inches at its widest part.
cochlea A fluid-filled, snail-shaped structure of the inner ear, containing hairs connected to the nerve endings for hearing.
compass A scientific instrument for finding direction, with a magnetic needle that is attracted to the earth’s magnetic poles.
compass housing The fluid-filled disk mounted on the base plate of a compass that can be rotated manually, the rim marked with the degrees of a circle (0° to 360°) and with letters for the cardinal directions N, S, E, and W.
compass needle A thin, magnetized strip of metal suspended on a pivot inside the compass housing that swings freely and points toward the earth’s magnetic poles. The side that points north is red.
condensation Changing from a gas to a liquid, as when water vapor is cooled and sticks to tiny particles or surfaces, forming water droplets.
contract To get smaller.
crystals Solids that have a definite chemical makeup, and a regular and repeated arrangement of their atoms. With space to grow freely they form flat surfaces (facets) that meet at an angle.
cumulonimbus A towering, dark, heaped-up cumulus cloud that can grow up to 14 miles high, and can produce violent thunderstorms, high winds and hail.
cumulus A white cloud with puffy heaps and a flat base, found below 6500 feet above the ground, seen on sunny days.
deposition The settling out and piling up of loose sand, rocks or other materials transported by agents like wind, water or glaciers.
direction of travel arrow An arrow on the base plate of an orienteering compass, extending from the rim of the compass housing to the edge of the base plate.
ear The hearing organ, which can take different forms in different animals.
ear canal The tube leading from the outer ear to the eardrum and internal parts of the ear.
eardrum The thin membrane inside the ear canal that vibrates when a sound wave reaches it, transferring the vibration to the bones of the middle ear.
echo A sound repeated by being reflected from a wall, mountain or other large, hard surface.
energy Any source of useable power such as solar radiation, fossil fuel, or electricity.
equator An imaginary line around the middle of the earth, dividing it into northern and southern halves.
erosion The wearing away and carrying off of rock, soil, sand or other material by agents like wind, water, glaciers.
evaporation Changing from a liquid to a gas, such as when water that is heated becomes water vapor.
expand To get larger.
fossil A remnant or trace of an organism of a past geologic age, such as an imprint or a skeleton or shell turned to stone and preserved in rock.
gas A state of matter in which molecules are loosely bonded and can spread out to fill any available space.
glacier A large, long-lasting mass of compacted snow and ice.
gravity The pull of objects toward each other, like the pull of the Earth that causes things to fall downward, and keeps us on the ground.
groundwater Water that is in the soil, in rocks and underground.
hammer bone The tiny hammer-shaped bone in the middle ear that conducts sound waves to the anvil bone.
igneous Rocks formed from the cooling and hardening of molten magma.
inner ear The innermost part of the ear that contains the cochlea and the semicircular canals, which are important for balance.
liquid A state of matter in which molecules are loosely-bonded and can slide past each other; a fluid.
magma Molten rock found deep inside the earth.
magnetic field An area of force surrounding a magnet. The Earth has a magnetic field because of currents within its molten metallic core.
mental map A picture in our mind of where things are located in a place we know well.
metamorphic Rocks formed when igneous, sedimentary or metamorphic rock is changed by heat and pressure.
middle ear The space between the eardrum and the inner ear that contains the three tiny bones that conduct sound waves to the inner ear.
mineral A naturally-occurring solid with a crystal form, that has a definite chemical makeup and that did not come from a living creature. Examples are quartz, diamond, mica, gold, talc.
navigation Finding your way; knowing how to travel to a particular place.
orbit The pathway of one object around another as the Earth’s pathway around the sun.
orientation Knowing one’s position in relation to the surroundings; knowing where you are in relation to where you want to go.
orienting arrow Cross-hatching or parallel lines on the compass housing, adjacent to the letter ‘N,’ that is used in setting the compass; also called “bed” or “shed.”
oxygen Colorless, odorless gas that forms about 21 percent of Earth’s atmosphere and is essential for living things to breathe.
pebble A rock smaller than 2.5 inches at its widest part, but larger than a grain of sand.
pinna The outer ear.
pitch How high or low a tone sounds.
poles The north and south ends of Earth.
precipitation Water returning to the earth from the air as rain, snow, sleet, hail or a mixture.
respiration Breathing; the process of taking in oxygen to supply energy for bodily functioning, releasing carbon dioxide and water as waste products.
revolve Travel in a path around a central body, as the earth revolving around the sun; orbit.
rotate Turn on an axis, like a top.
roundness A measure of how much the edges and corners of rock fragments have been ground down and smoothed from being transported in streams or glaciers.
seasons Parts of the year characterized by different weather patterns.
sediment Particles of sand, gravel, shells or other materials, that are carried and deposited by water, wind or ice.
sedimentary Rocks formed from the pressing and cementing together of particles such as clay, sand, rock fragments, or things that were once part of living things like shells and animal skeletons; rocks where fossils can be found.
sense of direction An awareness of where we are and how to get to another place.
wind sorting Movement of loose sediments by wind, smaller particles carried farther than larger, heavier ones.
solid A state of matter in which the molecules are tightly bonded and cannot move around, but can only vibrate in place.
sound Noise; anything we, or other animals, can hear.
sound wave Vibration that travels through air, water or solids.
stirrup bone The tiny bone in our middle ear, shaped like a stirrup, that conducts sound waves to the inner ear.
stratus A low layer of clouds covering much of the sky on overcast days.
sunlight Light from the sun; radiation from the sun that we can see.
transpiration The process of water moving upwards through a plant and being released into the air as water vapor.
vibration A rapid, repeated, back and forth motion.
water cycle Continual movement of water from the earth to the atmosphere and back again.
water vapor The gaseous form of water.
wind Moving air, mostly in a direction parallel to the ground.
wind direction The main direction from which a wind is blowing (e.g. a north wind blows from north to south).
Nearby Nature 