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Astronomy Chapter 2


constellation a region of the sky with well defined borders
celestial sphere the illusion of a sphere that encompasses the earth
North celestial pole point which lies directly over the North Pole
South celestial pole point which lies directly over the South Pole
celestial equator projection of Earth's equator into space
ecliptic path the sun follows
number of constellations 88
galactic plane our galaxy's disk of stars
local sky the sky as seen from where you are standing
horizon boundary between Earth and sky
zenith point directly overhead
meridian imaginary half-circle stretching from the horizon from N to S
azimuth direction of object along the horizon - measured in degrees
altitude position of object from between earth and sky
angular size angle that an object appears to span
angular distance angle that appears to separate two objects
arcminutes one degree divided by 60
arcseconds one arcminute divided by 60
circumpolar stars that never rise but make daily counterclockwise circles
latitude measures N to S
longitude measures E to W
prime meridian line of longitude at 0 degrees - runs through Greenwich, England
sky visibility sky varies with latitude
zodiac constellations along the ecliptic
Earth's orbit summer solstice, winter solstice, spring equinox, fall equinox
precession a gradual wobble that changes the orientation of Earth's axis
lunar phases new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter, waning crescent
synchronous rotation moon must rotate once as it makes a single orbit around the Earth
lunar eclipse earth's shadow falls on moon
solar eclipse moon's shadow falls on earth
nodes two points at which the moon crosses the surface of the earth
umbra sunlight is completely blocked
penumbra sunlight is partially blocked
total lunar eclipse moon passes through earth's umbra - moon turns red
partial lunar eclipse part of moon passes through earth's umbra
penumbral lunar eclipse moon passes thought earth's penumbra
total solar eclipse moon comes between sun and earth - moon looks black
partial solar eclipse moon appears red in a crescent form
annual eclipse a ring of sunlight surrounds the disk of the moon
eclipse seasons two periods where the nodes of the moon's orbit are aligned with the sun
saros cycle changing dates of eclipse seasons
Created by: sgw005