2: Celestial Sphere, Moon Phases

Celestial Sphere

imaginary giant sphere surrounding earth to help map all the objects in the sky (stars, planets, etc)

meridian

imaginary line (N-S), passes through zenith, marks when objects are at their highest point in the sky

zodiac

a band of constellations along the ecliptic, the path the son, moon, planets appear to follow across sky

circumpolar

stars that never set below the horizon at a specific location (ex: Polaris in Colorado)

altitude

how high an object appears in the sky, measured in degrees above horizon from 0 to 90

azimuth

the compass direction of an object in the sky, measured in degrees (0° = N, 90° = E, 180° = S, 270° = W).

declination (Dec)

latitude for celestial sphere, degrees away from celestial equator

Right ascension (RA)

longitude on celestial sphere, how far east an object is from “zero point” (near pisces), measured in hours, minutes, seconds

full moon

the phase when the entire face of the moon facing earth is lit by the sun

new moon

the phase where the moon is between the sun and earth so none of the face facing earth is lit

waxing

when the moon’s lit portion is growing

waning

when the moon’s lit portion is shrinking

polaris

the north star, appears fixed above north pole, used for navigation

aphelion

when earth is farthest from sun (early July)

perihelion

when earth is closest to sun (early January)

precession

slow wobble of earth’s axis (spinning top), takes 26,000 years to cycle, slowly shifts north star position

axial tilt

the tilt of earth’s axis relative to orbit around sun, about 23.5 degrees, causes seasons

eccentricity

how stretched out an orbit is (earth’s is near circular→small eccentricity)

order of moon phases

new→waxing→full→waning→new