Chapter 4 Flashcards
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.
Extrasolar planets
Planet orbiting a star other than the Sun.
Nebula
General term used for any “fuzzy” patch on the sky, either light or dark.
Solar nebula
The swirling gas surrounding the early Sun during the epoch of solar system formation, also referred to as the primitive solar system.
Nebular theory
One of the earliest models of solar system formation, dating back to Descartes, in which a large cloud of gas began to collapse under its ken gravity to form the Sun and planets.
Condensation theory
Currently favored model of solar system formation that combines features of the old nebula theory with new information about interstellar dust grains, which acted as condensation nuclei.
Condensation nuclei
Dust grains in the interstellar medium that act as seeds around which other materials can cluster. The presence of duct was very important in causing matter to clump up during the formation of the solar system.
Accretion
Gradual growth of bodies such as planers, by the accumulation of other, smaller bodies.
Planetesimals
Term given to objects in the early solar system that had reached the size of small moons, at which point their gravitational fields were strong enough to begin influencing their neighbors.
Protoplanets
Clumps of material, formed in the early stages of solar system formation, that was the forerunner of the planets we see today.
Fragmentation
The breaking up of a large object into many smaller pieces (for example, as the result of high-speed collisions between planetesimals and protoplanets in the early solar system.)
Protosun
The central accusation of material in the early stages of solar system formation, the forerunner of the present-day Sun
Planetary transits
One of eight major bodies that orbit the Sun, visible to use by reflected sunlight.
Super-earths
An extrasolar planet with a mass between 2 and 10 times that of Earth
Hot Jupiters
A massive, gaseous planet orbiting very close to its parent star
Selection effect
Observation bias in which a measured property of a collection of objects is due to the way in which the measurement was made rather than being intrinsic to the objects themselves.
Habitable zone
Three-dimensional zone of comfortable temperature (corresponding to liquid eater) that surrounds every star.
