Chapter 2 Key Terms
- accelerate
- to change velocity; to speed up, slow down, or change direction.
- apparent magnitude
- a measure of how bright a star looks in the sky; the larger the number, the dimmer the star appears to us
- astrology
- the pseudoscience that deals with the supposed influences on human destiny of the configurations and locations in the sky of the Sun, Moon, and planets
- celestial equator
- a great circle on the celestial sphere 90° from the celestial poles; where the celestial sphere intersects the plane of Earth’s equator
- celestial poles
- points about which the celestial sphere appears to rotate; intersections of the celestial sphere with Earth’s polar axis
- celestial sphere
- the apparent sphere of the sky; a sphere of large radius centered on the observer; directions of objects in the sky can be denoted by their position on the celestial sphere
- circumpolar zone
- those portions of the celestial sphere near the celestial poles that are either always above or always below the horizon
- cosmology
- the study of the organization and evolution of the universe
- ecliptic
- the apparent annual path of the Sun on the celestial sphere
- epicycle
- the circular orbit of a body in the Ptolemaic system, the center of which revolves about another circle (the deferent)
- geocentric
- centered on Earth
- heliocentric
- centered on the Sun
- horizon (astronomical)
- a great circle on the celestial sphere 90° from the zenith; more popularly, the circle around us where the dome of the sky meets Earth
- horoscope
- a chart used by astrologers that shows the positions along the zodiac and in the sky of the Sun, Moon, and planets at some given instant and as seen from a particular place on Earth—usually corresponding to the time and place of a person’s birth
- parallax
- the apparent displacement of a nearby star that results from the motion of Earth around the Sun
- planet
- today, any of the larger objects revolving about the Sun or any similar objects that orbit other stars; in ancient times, any object that moved regularly among the fixed stars
- precession (of Earth)
- the slow, conical motion of Earth’s axis of rotation caused principally by the gravitational pull of the Moon and Sun on Earth’s equatorial bulge
- retrograde motion
- the apparent westward motion of a planet on the celestial sphere or with respect to the stars
- year
- the period of revolution of Earth around the Sun
- zenith
- the point on the celestial sphere opposite the direction of gravity; point directly above the observer
- zodiac
- a belt around the sky about 18° wide centered on the ecliptic
This book was adapted from the following: Fraknoi, A., Morrison, D., & Wolff, S. C. (2016). Key Terms. In Astronomy. OpenStax. https://openstax.org/books/astronomy/pages/2-key-terms under a Creative Commons Attribution License 4.0
Access the entire book for free at https://openstax.org/books/astronomy/pages/1-introduction
