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the study of the moon, stars, and other objects in space


an imaginary line that passes through Earth's center and the north and south poles, about which Earth rotates


the movement of an object around another object


the path of an object as it revolves around another object in space


a measurement of distance from the equator, expressed in degrees north or south


The two days of the year on which the noon sun is directly overhead at either 23.5 degrees South or 23.5 degrees North


the two days of the year on which neither hemisphere is tilted toward or away from the sun

vernal equinox

the day of the year that marks the beginning of spring in the northern hemisphere

autumnal equinox

The day of the year that marks the beginning of fall in the Northern hemisphere


one of the different shapes of the moon as seen from Earth

solar eclipse

the blocking of sunlight to earth that occurs when the moon is directly between the sun and earth


the darkest part of a shadow


the part of a shadow surrounding the darkest part

lunar eclipse

the blocking of sunlight to the moon that occurs when Earth is directly between the sun and the moon


The rise and fall of the level of water in the ocean


attractive force between two objects that depends on the masses of the objects and the distance between them

spring tide

a tide with the greatest difference between low and high tides

neap tide

a tide with the least difference between low and high tides

nuclear fusion

the process by which hydrogen atoms join together to form helium, releasing energy


The central part of the sun, where nuclear fusion takes place


the inner layer of the suns atmosphere


The middle layer of the sun's atmosphere


outer layer of the sun's atmosphere

solar wind

a stream of electrically charged particles produced by the sun's corona


areas of gas on the sun's surface that are cooler than the gases around them


A loop of gas that protrudes from the sun's surface, linking parts of sunspot regions

solar flares

an explosion of hydrogen gas from the sun's surface that occurs when the loops in sunspot regions suddenly connects

continental drift

the hypothesis that the continents slowly move across Earth's surface


a trace of an ancient organism that has been preserved in rock

mid-ocean ridge

an undersea mountain chain where new ocean floor is produced; a divergent plate boundary


a device that determines the distance of an object under water by recording echoes of sound waves

deep-ocean trench

a deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle


the process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary

sea-floor spreading

the process by which molten material adds new oceanic crust to the ocean floor


The point beneath Earth's surface where rock breaks under stress and causes an earthquake


the point on Earth's surface directly above an earthquake's focus


a device that records ground movements caused by seismic waves as they move through Earth


The measurement of an Earthquake's strength based on seismic waves and movement along faults

Mercalli scale

A scale that rates earthquakes according to their intensity and how much damage they cause

Richter Scale

a scale that rates seismic waves as measured by a particular type of mechanical seismograph

moment magnitude scale

a scale that rates earthquakes by estimating the total energy released by an earthquake

seismic waves

vibrations that travel through Earth carrying the energy released during an earthquake

P waves

A type of seismic wave that compresses and expands the ground

S waves

A type of seismic wave that moves the ground up and down or side to side

surface waves

a type of seismic wave that forms when P waves and S waves reach Earth's surface


the spinning motion of a planet on its axis


the partial or total blocking of one object in space by another


the name of the single landmass that broke apart 200 million years ago and gave rise to today's continents

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