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Chapter 28
Term | Definition |
---|---|
planetesimal | objects hundreds of kilometers in diameter |
retrograde motion | the apparent backward movement of a planet |
ellipse | an oval shape that is centered on two points instead of a single point, as in a circle |
astronomical unit | the average distance between the Sun and Earth |
eccentricity | the ratio of the distance between the foci to the length of the major axis |
terrestrial planet | the four inner planets |
scarp | Mercury's planetwide system of cliffs |
gas giant planet | large, gaseous planet that is very cold at its surface |
liquid metallic hydrogen | a form of hydrogen that has properties of both a liquid and a metal and can only exist under conditions of very high pressure |
belt | low, warm, dark-colored clouds that sink |
zone | high, cool, light-colored clouds that rise |
dwarf planet | an object that, due to its own gravity, is spherical in shape, orbits the sun, is not a satellite, and has not cleared the area of its orbit of smaller debris |
meteoriod | an asteriod fragment, or any other interplanetary material that enters Earth's atmosphere |
meteor | a metereoroid that passes through the atmosphere, and heated by friction and burns, producing a streak of light |
meterorite | a meteoroid that does not brurn up completely and part of it strikes the ground (it is the part that hits the ground) |
Kuiper belt | samll solar system bodies that are mostly rock and ice, lies outside the orbit of Neptune |
comet | small, icy bodies that have highly eccentric orbits around the Sun |
meteor shower | bright streaks of light caused from when Earth crosses the trail of a comet and particles left in the trail burn in Earth's upper atmosphere |