Astronomy – Space Definitions – Flashcards
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angle of insolation
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The angle between Earth's surface and incoming rays of sunlight; angle of the sun above the horizon
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Antarctic Circle
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The latitude (66.5°S) south of which the sun does not rise on the Southern Hemisphere's winter solstice; the latitude (66.5°S) south of which the sun is in the sky for 24 hours on the Southern Hemisphere's the summer solstice
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Arctic Circle
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The latitude (66.5°N) north of which the sun does not rise on the Northern Hemisphere's winter solstice; The latitude (66.5°N) north of which the sun is in the sky for 24 hours on the Northern Hemisphere's summer solstice
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asteroid
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An irregularly shaped rocky mass that is smaller than a planet and occupies an orbit around the sun; most are found between the orbits of Mars and Jupiter
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astronomy
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The study of Earth's motions and the objects beyond Earth, such as planets and stars
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axis
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An imaginary line that passes through Earth's North and South Poles
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azimuth
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The compass direction specified as an angle. Azimuth starts at 0° at due North and progresses through East (90°), South (180°), West (270°), and back to North (360°, or 0°).
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big bang
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The theory that the universe formed as a concentration of matter expanded explosively
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calorie
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The energy absorbed when the temperature of 1 gram of water increases 1 Celsius degree
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celestial object
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Things seen in the sky that are outside Earth's atmosphere
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comet
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An object made of ice and rock fragments that revolves around the sun usually in a highly eccentric orbit; it may be visible periodically in the night sky as a small spot of light with a long tail
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conduction
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The movement of heat that occurs as heated molecules pass their vibrational energy to nearby molecules.
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convection
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A form of heat flow that moves matter and energy as density currents under the influence of gravity
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convection cell
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The pattern of circulation that involves vertical and horizontal flow
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Coriolis Effect
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The apparent curvature of the path of winds and ocean currents as they travel long distances over Earth's surface; caused by Earth's rotation
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cosmic background radiation
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Weak electromagnetic radiation (radio waves) left over from the formation of the universe (big bang)
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crater
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A bowl-shaped depression at the top of a volcano caused by an explosive eruption or the impact of an object from space.
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Doppler Effect
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The apparent change in frequency and wavelength of energy radiated by a source as a result of the motion of the source or the observer
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duration of insolation
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The amount of time the sun is visible in the sky, or the number of hours between sunrise and sunset
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eccentricity
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A measure of the elongation of an ellipse
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eclipse
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The partial or complete hiding of one celestial object by another. (An eclipse of the moon occurs when the moon orbits into Earth's shadow. An eclipse of the sun occurs when the moon's orbit takes it directly between Earth and the sun.)
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elements
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The basic substances that are the building blocks of matter
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ellipse
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A closed curve formed around two fixed points such that the total distance from any point on the curve to both fixed points is constant
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equator
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An imaginary line that circles Earth halfway between the North and South Poles
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equilibrium
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A state of balance
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equinox
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One of the two days on which the sun rises due east and sets due west, on which the length of day and night are equal, on which the sun's vertical rays are at the equator; the first day of spring or fall
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frequency
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A measure of how many waves pass a given point in a given period of time
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galaxy
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A huge group of stars held together by gravity
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gravity
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The force of attraction between objects
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Greenwich Mean Time
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The basis of standard time throughout the world; based on measurements of the position of the sun in Greenwich, England
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hazard
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An event that places people in danger of injury, loss of life, or property damage
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inertia
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The tendency of an object at rest to remain at rest or an object in motion to move at a constant speed in a straight line unless acted on by an unbalanced force
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insolation
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Solar energy that reaches Earth (incoming solar radiation)
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Jovian planet
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A planet whose composition is similar to Jupiter's; also know as a gas giant
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latitude
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The angular distance north or south of the equator
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light-year
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The distance electromagnetic energy can travel in one year, approximately 6 trillion miles (10 trillion km)
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longitude
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The angular distance east or west of the prime meridian
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luminosity
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The total energy output of a star; absolute brightness
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major axis
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The distance across an ellipse measured at it widest point
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meteor
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A streak of light produced as a meteoroid burns due to friction with Earth's atmosphere
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Milky Way Galaxy
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The group of billions of stars that includes the sun and our solar system, it is visible as a faint band of light across the night sky
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neap tides
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The smallest tidal range, which occurs when the sun and moon are at right angles to Earth
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nuclear fusion
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The process by which the nuclei of light elements, such as hydrogen, under intense heat and pressure form the nuclei of heavier elements, such as helium
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oblate
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Slightly flattened at the poles
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phase
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The observed shape of the lighted portion of a celestial object, for example, the moon or Venus
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phases of matter
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The states of matter— solid, liquid, and gas
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prime meridian
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The north-south line through Greenwich, England, from which longitude is measured
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radiation
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The transfer of energy in the form of electromagnetic waves
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redshift
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A displacement of the spectral lines of very distant stars and galaxies, an increase in the wavelength of starlight caused by rapid relative motion of the star away from the observer. (See Doppler effect)
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reflection
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The process by which light bounces off a surface or material
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refraction
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The bending of light and other energy waves as they enter a substance of different density
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satellite
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An object in space that revolves around another object as a result of gravity
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scattering
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The reflection of light in many different directions
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solar time
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Time based on observations of when the sun reach its highest point and crosses a north-south line through the sky
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spring tides
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The largest tidal range, which occurs when Earth, the sun, and the moon are in a line with one another (not related to Earth's seasons)
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summer solstice
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The name generally applied to the day of the year with the longest period of sunlight. (For observers in the Northern Hemisphere, this occurs near June 21. The Northern Hemisphere summer solstice occurs when the vertical rays of the sun are at the Tropic of Cancer. In the Southern Hemisphere, the summer solstice occurs in December when the vertical rays of the sun are at the Tropic of Capricorn.)
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terrestrial planet
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A planets whose composition is similar to Earth's
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tidal range
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The difference between the lowest water level and the highest water level
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tides
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The twice- (or once-) daily cycle of change in sea level caused by the gravitational influence of the moon and sun on Earth's oceans
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Tropic of Cancer
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The greatest latitude north of the equator reached by the sun's vertical ray; 23.5°N
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Tropic of Capricorn
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The greatest latitude south of the equator reached by the sun's vertical ray; 23.5°S
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velocity
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Speed; change in distance divided by change in time; sometimes velocity is used to include both speed and direction.
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vertical rays
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Sunlight that strikes Earth's surface at an angle of 90°
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winter solstice
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The name generally applied to the day of the year with the shortest period of sunlight. (For observers in the Northern Hemisphere, this occurs near December 22. The Northern Hemisphere winter solstice occurs when the vertical rays of the sun are at the Tropic of Capricorn. In the Southern Hemisphere, the winter solstice occurs in June when the vertical rays of the sun are at the Tropic of Cancer.)
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zenith
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The point in the sky directly over an observer's head
