| A | B |
|---|
| Summer solstice | time of year when the Norhtern Hemisphere has its longest day and the Southern Hemisphere has its shortest day; beginning of summer in the Northern Hemisphere |
| Winter solstice | time of year when the Norhtern Hemisphere has its shortest day and the Southern Hemisphere has its longest day; beginning of winter in the Northern Hemisphere |
| Vernal equinox | time of year when day and night are of equal length; beginning of spring in the Norhtern Hemisphere |
| Autumnal equinox | time of year when day and night are of equal length; beginning of autumn in the Northern Hemisphere |
| Magnetosphere | magnetic field around planet |
| Van Allen radiation belts | two doughnut-shaped regions of charged particles formed when the Earht's magnetosphere traps some of the particles in the solar wind |
| Aurora | bands or curtains of colored lights produced when particles trapped by the Van Allen radiation belts collide with particles in the upper atmosphere |
| Highlands | mountain ranges on the moon |
| Maria | smooth, lowland plains on the moon |
| Rille | valley on the moon |
| Perigee | Point of a satellite's orbit closest to Earth |
| Apogee | Point of a satellite's orbit farthest from Earth |
| Solar eclipse | Blocking of the sun that occurs when the new moon comes directly between the sun and the Earth |
| Umbra | Inner part of a shadow |
| Penumbra | Outer part of a shadow |
| Lunar eclipse | blocking of the moon that takes place when the Earth comes directly between the sun and the full moon |
| Tide | rise and fall of the oceans caused by the moon's gravitational pull on the Earth |
| Spring tide | Higher than usual high tide that occurs during the full moon and new moon phases |
| Neap tide | lower than usual high tides that occurs during the first and last quarter phases |
| Geosynchronous orbit | orbit in which a satellite's rate of revolution exactly matches the Earth's rate of rotation |
| Salinity | term used to describe the amount of dissolved salts in ocean water |
| Continental margin | area where the underwater edge of a continent meets the ocean floor |
| Continental shelf | relatively flat part of a continental margin that is covered by shallow ocean water |
| Continental slope | part of the continental margin at the edge of a continental shelf where the ocean floor plunges steeply 4 to 5 kilometers |
| Continental rise | part of a continental margin that separates a continental slope from the ocean floor |
| Turbidity current | flow of ocean water that carries large amounts of sediments |
| Thermocline | zone in which the temperature of ocean water drops rapidly |
| Crest | highest point of a wave |
| Trough | lowest point of a wave |
| Wavelength | horizontal distance between two consecutive crests or two consecutive troughs |
| Tsunami | ocean wave caused by an earthquake |
| Surface current | ocean current caused mainly by wind patterns |
| Deep current | ocean current caused mainly by differences in the density of water deep in the ocean |
| Upwelling | rising of deep, cold currents to the ocean surface |
| Guyot | flat-topped seamount |
| Coral reef | large mass of limestone rocks surrounding a volcanic island in tropical waters near a continental shelf |
| Fringing reef | coral reef that touches the shoreline of a volcanic island |
| Barrier reef | Coral reef separated from the shore of an island by an area of shallow water called a lagoon |
| Atoll | ring of coral reefs surrounding an island that has been worn away and has sunk beneath the surface of the ocean |
| Seamounts | underwater volcanic mountain on the ocean floor |
