1.6: Key Terms
- Page ID
- 130851
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- accelerate: to change velocity, to speed up, slow down, or change direction
- astronomical unit (AU): the unit of length defined as the average distance between Earth and the Sun, about 1.5 × 108 kilometers
- control: a part of an experiment that does not change during the experiment
- deductive reasoning: a form of logical thinking that uses a general statement to forecast specific results
- eccentricity: in an ellipse, the ratio of the distance between the foci to the major axis
- ellipse: a closed curve for which the sum of the distances from any point on the ellipse to two points inside, called the foci, is always the same
- epicycle: the circular orbit of a body in the Ptolemaic system, the center of which revolves about another circle, the deferent
- falsifiable: able to be disproven by experimental results
- geocentric model: a model of the universe with Earth at its center and the Sun, Moon, and stars orbiting the Earth in perfect circles, geo means Earth and is of Greek origin
- gravity: the mutual attraction of material bodies or particles
- heliocentric model: the model of the Solar System with the Sun at the center and the planets, including Earth, orbiting around the Sun, Helios is the Greek proper name for the Sun
- hypothesis: a suggested explanation for an event, which can be tested
- inductive reasoning: a form of logical thinking that uses related observations to arrive at a general conclusion
- Kepler’s first law: each planet moves around the Sun in an orbit that is an ellipse, with the Sun at one focus of the ellipse
- Kepler’s second law: the straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time
- Kepler’s third law: the square of a planet’s orbital period is directly proportional to the cube of the semimajor axis of its orbit
- law: a description, often in the form of a mathematical formula, for the behavior of some aspect of nature under certain specific conditions
- major axis: the maximum diameter of an ellipse
- model: representation of something that is often too difficult or impossible to display directly
- natural science: a field of science that studies the physical world, its phenomena, and processes
- Newton’s first law: every object will continue to be in a state of rest or move at a constant speed in a straight line unless it is compelled to change by an outside force
- Newton’s second law: the change of motion of a body is proportional to and in the direction of the force acting on it
- Newton’s third law: for every action there is an equal and opposite reaction or: the mutual actions of two bodies upon each other are always equal and act in opposite directions
- parallax: the apparent displacement of a nearby star that results from the motion of Earth around the Sun
- peer-reviewed article: a scientific report that is reviewed by a scientist’s colleagues before publication
- physical science: a field of science, such as astronomy, physics, and chemistry, that studies nonliving matter
- retrograde motion: the apparent westward motion of a planet on the celestial sphere or with respect to the stars
- science: knowledge that covers general truths or the operation of general laws, especially when acquired and tested by the scientific method
- scientific method: a method of research with defined steps that include experiments and careful observation
- semimajor axis: half of the major axis of a conic section, such as an ellipse
- theory: a thoroughly tested and confirmed explanation for observations or phenomena
- variable: a part of an experiment that can vary or change