4.7: Key Terms
- Page ID
- 121550
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- Apoapsis: The farthest point an orbiting object can be from the object it is orbiting; its opposite is periapsis. See apogee, aphelion.
- Asteroids: Metallic, rocky objects without atmospheres that orbit the Sun, but are too small to be called planets. Small objects in the Solar System, such as asteroids, are sometimes called minor planets or small bodies.
- Asteroid Belt: The region of the orbital plane of the Solar System located between the orbits of Mars and Jupiter which is occupied by numerous minor planets (asteroids) and the dwarf planet Ceres.
- Astronomical Unit (au or AU): A unit of length approximating the distance from Earth to the Sun, defined as 149,597,870.7 km (92,955,807.3 miles).
- Comets: A small body, of mostly ice and dust, in orbit around the Sun or passing through the solar system in large orbits. While passing near the Sun, the comet's vaporized ice becomes its two tails, a bright white one composed of dust, and a blue one made up of ionized gas.
- Cosmic dust: Irregularly shaped grains of carbon and/or silicates measuring a fraction of a micron across. Dust is most evident by its absorption, causing large dark patches in regions of our Milky Way galaxy and dark bands across other galaxies.
- Density: The mass per unit volume of a substance or object.
- Diameter: Any straight line between two points on the circumference of a circle that passes through the center of the circle. Used in astronomy to measure the size of a spherical object.
- Mass: The quantity of matter in a substance or object; measured in kilograms.
- Matter: Material substance that constitutes the observable universe and, together with energy, forms the basis of all objective phenomena.
- Meteor: Any of the small particles of matter in the Solar System that are directly observable only by their incandescence from frictional heating on entry into the atmosphere. Also known as a shooting star.
- Meteorite: A meteor that reaches the surface of the earth without being completely vaporized.
- Moon: A large body orbiting a planet. The general term is moon, while Earth's moon is called the Moon.
- Oort Cloud: A spherical shell of cometary bodies believed to surround the sun far beyond the orbit of Pluto and from which some are dislodged when perturbed (as by a passing star) to fall toward the sun.
- Orbit: The regularly repeated elliptical course of a celestial object or spacecraft about a star, planet, or moon. Also, a complete circuit round an orbited body.
- Orbital Period: The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In equations orbital period is often represented by P for period.
- Planet: A planet in the Solar System is a celestial body that: is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and has cleared the neighborhood around its orbit.
- Planetary Differentiation: The separation of different constituents of planetary materials resulting in the formation of distinct compositional layers. Denser material tends to sink into the center and less dense material rises toward the surface.
- Planetary Ring: A disk or ring orbiting an astronomical object that is composed of solid material such as dust and moonlets. Rings are a common component of satellite systems around the outer planets of the Solar System. A planet with a ring may be called a ringed planet or part of a ring system.
- Planetary System: A group of smaller bodies (such as planets or asteroids) that orbit one or more stars.
- Radius: Half of the diameter, or the distance from the center of a spherical object to its surface.
- Star: A large ball of gas that creates and emits its own radiation.
- Sun: The star in the center of the Solar System. Our star is called the Sun. A star in a different planetary system is sometimes called a sun.
- Volume: A three-dimensional measure of space that comprises a length, a width and a height. It is measured in units of cubic centimeters (cm3) in metric. When measuring an object, volume represents the amount of space that object occupies.