41 terms

Chapter 2 - Knowing the Heavens

From Chapter Two of Universe (9th Ed.)
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Antarctic Circle
A circle of latitude 23 1/2° north of Earth's south pole.
Apparent Solar Day
The interval between two successive transits of the Sun's center across the local meridian.
Apparent Solar Time
Time reckoned by the position of the sun in the sky.
Arctic Circle
A circle of latitude 23 1/2° south of Earth's north pole?
Autumnal Equinox
The intersection of the elliptic and the celestial equator where the Sun crosses the equator from north to south. Also used to refer to the date on which the Sun passes through this intersection.
Celestial Equator
A great circle on the celestial sphere 90° from the celestial poles.
Celestial Sphere
An imaginary sphere of very large radius centered on an observer; the apparent sphere of the sky.
Circumpolar
A term describing a star that neither rises nor sets but appears to rotate around one of the celestial poles.
Constellation
A configuration of stars in the same region of the sky.
Declination
Angular distance of a celestial object north or south of the celestial equator.
Diurnal Motion
Any apparent motion in the sky that repeats on a daily basis, such as the rising and setting of stars.
Ecliptic
The apparent annual path of the sun on the celestial sphere.
Ecliptic Plane
The plane of the Earth's orbit around the sun.
Epoch
The date used to define the coordinate system for objects on the day.
Equinox
One of the intersections of the ecliptic and the celestial equator. Also used to refer to the date on which the Sun passes through such an intersection.
Lower Meridian
The half of the meridian that lies below the horizon.
Mean Solar Day
The interval between successive meridian passages of the mean Sun; the average length of a solar day. (24 hours)
Mean Sun
A fictitious object that moves eastward at a constant speed along the celestial equator, completing one circuit of the sky with respect to the vernal equinox in one tropical year.
Meridian
The great circle on the celestial sphere that passes through an observer's zenith and the north and south celestial poles.
Meridian Transit
The crossing of the meridian by any astronomical object.
North Celestial Pole
The point directly above the earth's north pole where Earth's axis of rotation, , if extended, would intersect the celestial sphere.
Positional Astronomy
The study of the apparent positions of the planets and stars and how those positions change.
Precession
A slow, conical motion of the Earth's axis of rotation caused by the gravitational pull of the Moon and Sun on the Earth's equatorial bulge.
Precession of Equinoxes
The slow westward motion of the equinoxes along the ecliptic due to the procession of Earth.
Right Ascension
The coordinate for measuring the east-west positions of objects on the celestial plane.
Sidereal Clock
A clock that measures sidereal time.
Sidereal Day
The interval between successive meridian passages of the vernal equinox.
Sidereal Time
The time reckoned by the location of the vernal equinox.
Sidereal Year
The orbital period of Earth about the Sun with respect to the stars.
South Celestial Pole
The point directly above the earth's south pole where Earth's axis of rotation, if extended, would intersect the celestial sphere.
Summer Solstice
The point of the ecliptic where the Sun is farthest north of the celestial equator. Also used to refer to the date on which the Sun passes through this point.
Time Zone
A region of earth where, by agreement, all clocks have the same time.
Tropical Year
The period of revolution of Earth about the Sun with respect to the vernal equinox.
Tropic of Cancer
A circle of latitude 23 1/2°, north of the Earth's equator.
Tropic of Capricorn
A circle of latitude 23 1/2°, south of the Earth's equator.
Upper Meridian
The half of the meridian that lies above the horizon.
Vernal Equinox
The point on the ecliptic where the Sun crosses the celestial equator from south to north. Also used to refer to the date on which the Sun passes through this intersection.
Winter Solstice
The point on the ecliptic where the Sun reaches its greatest distance south of the Celestial equator. Also used to refer to the date on which the sun passes through this point.
Zenith
The point on the celestial sphere directly overhead an observer.
Zodiac
A band of 12 constellations around the sky centered on the elliptic.
Celestial Poles
The points about which the celestial sphere appears to rotate. (See also North/South Celestial Pole)