Chapter 4 Flashcards
(40 cards)
Solar System
The Sun and all the bodies that orbit it–
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, their moons, the asteroids, the Kuiper belt, and the comets.
Density
Ratio of the universe’s actual density to the critical value corresponding to zero curvature.
Terrestrial planets
One of the four innermost planets of the solar system, resembling Earth in general physical and chemical properties.
Jovian planets
One of the four giant outer planets of the solar system, resembling Jupiter in physical and chemical composition.
Asteroids
One of thousands of very small members of the solar system orbiting the Sun between the orbits of Mars and Jupiter. Often referred to as “minor planets.”
Meteoroids
Chunk of interplanetary debris prior to encountering Earth’s atmo-sphere
Comets
A small body, composed mainly of ice and dust, in an elliptical orbit around the Sun. As it comes close to the Sun, some of its material is vaporized to form a gaseous head and extended tail.
Kuiper belt
A region in the plane of the solar system outside the orbit of Neptune where most short-period comets are thought to originate.
Dwarf planet
A body that orbits the Sun, is massive enough that its own gravity has caused its shape to be approximately spherical, but is insufficiently massive to have cleared other bodies from “the neighborhood” of its orbit.
Asteroid belt
Region of the solar system, between the orbits of Mars and Jupiter, in which most asteroids are found.
Trojan asteroids
One of two groups of asteroids that orbit at the same distance from the Sun as Jupiter, 60 degrees ahead of and behind the planet.
Earth-crossing asteroids
An asteroid whose orbit crosses that of Earth. Earth-crossing asteroids are called Apollo asteroids, after the first asteroid of this type discovered.
Tail
Component of a comet that consists of material streaming away from the main body, sometimes spanning hundreds of millions of kilometers. May be composed of gas or ionized gases.
Nucleus
Dense, central region of an atom containing both photons and neutrons and orbited by one or more electrons. The region of ice and dust that composes the central region of the head of a comet. The dense central core of a galaxy.
Coma
An effect occurring during the formation of an off-axis image in a telescope. Stars whose light enters the telescope at a large angle acquire comet-like tails on their images. The brightest part of a comet, often referred to as the “head.”
Hydrogen envelope
An invisible sheath of gas engulfing the coma of a comet, usually distorted by the solar wind and extending across millions of kilometers of space.
Iron tail
Thin stream of ionized gas that is pushed away from the head of a comet by the solar wind. It extends directly away from the Sun. Often referred to as a plasma tail.
Dust tail
The component of a comet’s tail that is composed of dust particles.
Solar wind
An outward flow of fast-moving charged particles from the Sun.
Oort cloud
Spherical halo of material surrounding the solar system out to a distance of about 50,000 AU; where most comets reside
Kuiper belt
A region in the plane of the solar system outside the orbit of Neptune where most short-period comets are thought to originate.
Meteorite
Any part of a meteoroid that survives passage through the atmosphere and lands on the surface of Earth.
Meteoroid swarm
Pebble-sized cometary fragments dislodged from the main body, moving in nearly the same orbit as the parent comet.
Micrometeoroids
Relatively small chunks of interplanetary debris ranging from dust-particle size to pebble-sized fragments.
