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36 Cards in this Set

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constellation
groups of stars (we have 88 official ones)
asterism
less formally defined grouping of stars (i.e.; Big Dipper)
magnitude scale
astronomers use this to measure the brightness of stars (First appeared in writings of Ptolemy, 140 A.D., but most attribute to Greek astronomer Hipparchus (160-127 BC)
apparent visual magnitude
numbers that describe how bright the stars look to human eyes observing from Earth (The smaller the number, the brighter the star)
scientific model
a carefully devised mental conception of how something works (Does not have to be true to be useful, i.e.; celestial sphere)
celestial sphere
an imaginary sphere of very large radius surrounding Earth and to which the planets, stars, sun, and moon seem to be attached
horizon
the line that marks the apparent intersection of Earth and sky
zenith
the point on the sky directly overhead
nadir
the point on the bottom of the sky directly under your feet
north celestial pole
the point on the celestial sphere directly above Earth's North Pole
south celestial pole
the point of the celestial sphere directly above Earth's South Pole
celestial equator
the imaginary line around the sky directly above Earth's equator
north point
the point on the horizon directly below the North celestial pole; exactly north
south point
the point on the horizon directly above the south celestial pole; exactly south
east point
the point on the eastern horizon exactly halfway between the noth point and the south point; exactly east
west point
the point on the western horizon exactly halfway between the north point and the south point; exactly west
angular distance
a measure of the separation between two objects in the sky; numerically equal to the angle in degrees between two lines extending from the observer's eye to the two objects
minute of arc
an angular measure; each degree is divided into 60 _
second of arc
an angular measure; each minute of arc is divided into _
angular diameter
a measure of the size of an object in the sky; numerically equal to the angle in degrees between two llines extending from the observer's eye to opposite edges of the objects
circumpolar constellation
any of the constellations so close to the celestial pole that they never set (or never rise) as seen from a given latitude
precession
the slow change in the direction of Earth's axis of rotation; one cycle takes nearly 26,000 years
rotation
the turning of a body about an axis through its center (Earth does this once a day, and it causes the day/night cycle)
periphelion
about January 4, Earth is at its closest point to the sun (only 1.7% closer than average)
revolution
the motion of a body around a point located outside the body (Earth does this around the sun once a year, and it causes the cycle of seasons)
ecliptic
the apparent path of the sun in its yearly motion around the sky (The projection of Earth's orbit on the sky)
vernal equinox
the place on the celestial sphere where the sun crosses the celestial equator moving northward; also the time of year when the sun crosses this point, about March 21, and spring begins in the Northern Hemisphere
summer solstice
the point on the celestial sphere where the sun is at its most northerly point; the time when the sun passes this point, about June 22, summer begins in the northern hemisphere
autumnal equinox
point on the celestial sphere where the sun crosses the celestial equator going southward; time when sun reaches this point and autumn begins in the Northern hemisphere; about September 22
winter solstice
the point on the celestial sphere where the sun is farthest south; also, the time of year when the sun passes this point, about December 22, and winter begins in the northern hemisphere
aphelion
About July 4- Earth is most distant from the sun, only 1.7% farther than average
evening star
any planet visible in the evening sky
morning star
any planet visible in the sky shortly before sunrise
zodiac
the band around the sky centered on the ecliptic within which the planets move
horoscope
chart showing the positions of the sun, moon, planets, and constellations at the time of a person's birth; used in astrology to attempt to read character or foretell the future
Milkankovitch hypothesis
hypothesis that small changes in Earth's orbital and rotational motions cause the ice ages