L3 patterns in the sky

light travel speeds to different places

Moon one second, Sun eight minutes, Sirius eight years, Andromeda Galaxy 2.5 million years

constellation

region of the sky, 88 fill the sky

ecliptic

Sun’s apparent path through the celestial sphere

north celestial pole

directly above Earth’s

celestial equator

a projection of Earth’s onto the sky, going from due west to east

location in local sky specified by

altitude (above horizon) and direction (along horizon)

zenith

straight up (90º altitude)

meridian

line along the sky from due north to south

angular measurements

full circle = 360 degrees, each degree divided into 60 arcminutes and 3600 arcseconds

angular size in degrees =

(physical size / distance) * 360º/2pi radians

sidereal day

one rotation of earth with respect to itself

solar day

one rotation of earth with respect to the Sun i.e. sunrise to sunrise

constellations we see depend on

latitude and time of year because Earth’s orbit changes Sun’s apparent location

stars near the north celestial pole are

circumpolar - never set

stars near the south celestial pole

are never seen

latitude

position north or south of equator

longitude

position east or west of prime meridian

if north star is 50º above your horizon, where are you

latitude 50º N

over course of year, the Sun appears to move _ along the ecliptic

eastward

at midnight, the stars on our meridian are

opposite the Sun in the sky

seasons caused by

Earth’s axial tilt affecting the directness of sunlight

recognition of solstices and equinoxes

summer solstice: highest path, rise and set at most extreme north of due east

winter solstice: lowest path, rise and set at most extreme south of due east

equinoxes: sun rises precisely due east and sets due west

why does earth’s axial orientation change over time and how long

precesses like a spinning top, over about 26,000 years

what causes lunar phases

Moon’s orbit around Earth

what is always true about the moon regardless of phase

one half is always illuminated and half is dark

we always see the near side

as moon orbits

we see a changing view of the bright and dark faces, only seeing the illuminated half during a full moon

waxing moons visible in

afternoon/evening, rising later and getting fuller each day

waning moons visible in

late night/morning, setting later and getting less full each day

moon’s synchronous rotation

rotates exactly once with each orbit aka tidal locking

lunar eclipse

earth’s shadow falls on Moon

solar eclipse

moon’s shadow falls on Earth

when can lunar eclipses occur and what are types

only at full moon; penumbral, partial, total

when can solar eclipses occur

only at new moon; partial, total, annular

why don’t we have eclipses at every new and full moon

moon’s orbit is tilted 5 degrees to ecliptic plane, reulting in two eclipse seasons each year

conditions for eclipses

it must be full or new moon AND the moon must be at or near one of the two points in its orbit where it crosses the ecliptic plane