| A | B |
|---|
| aphelion | point in the orbit of a planet at which the planet is farthest from the sun. |
| autumnal equinox | beginning of the fall saeson. |
| axis | imaginary staight line running through the earth from pole to pole |
| core | cener of a planetary body such as the earth. |
| moho | the mohorovicic discontinuity boundary between the earths cr |
| mantle | zone of rock beiow the earths crust. |
| crust | outermost layer of solid earth |
| gravity | force of attraction between all matter in the universe |
| International Date Line | line running from north to south through the Pacific Ocean where the date changes from one day to the next |
| law of gravitation | principle that the force of attraction between two objects depends on the masses and the distance between the objects |
| magnetosphere | a region of space that is affected by the earth's magnetic field |
| perihelion | point in the orbit |
| polar orbit | orbit that passes over the earth's North and South Poles |
| precession | slow circular motion of the earth's axis as it turns in space that traces a circle in every 26 thousand years |
| winter solstice | the beginning of winter |
| vernal eqinox | the beginning of spring |
| summer solstice | the beginning of summer |
| standard time zone | one of 24 regions of the earth in which noon is set at the time when the sun is highest over the center of the region |
| shadow zone | location on the earth's surface where no seismic waves or only P waves can be detected |
| seismic wave | vibration that travels through the earth |
| satellite | object in orbit around a body with a larger mass |
| rotation | spinning of a planet on its axis |
| revolution | movement of a planet around the sun |
| daylight saving time | system in which clocks are setone hour ahead of standard time from April to October |
| geosynchronous orbit | orbit directly above the esrth's equator and moving in the direction of the earth's rotation |
