astronomy II finals review

apparent motions

the way in which celestial objects appear to move across the sky

celestial sphere

the visible portion of the sky that celestial objects appear to travel on

zenith

highest point on the celestial sphere which is directly over the observer

horizon

the edge of the visible portion of the celestial sphere

direction of celestial objects across the sky

All objects [except Polaris] appear to move across the celestial sphere

from east to west at 15 º/hour or 360º/24 hours

altitude

angular distance above the horizon [0º to 90º]

azimuth

angular distance along the horizon measured from due north [0º to 360º]

heliocentric model

current model of the solar system where the Sun is at the center. Also called the Copernican Model

rotation

why we experience day and night. earth rotates west to east, counterclockkwise

earth’s tilt

23.5 degrees, causes seasons. changes the angle and intensity of sunlight.

parallelism of earth’s axis

Earth’s tilted axis of 23.5º is always pointed to the same location in the sky giving us our different seasons

giant impact theory

a planetesimal [size of Mars] struck the earth, ejecting large volumes of matter that condensed to form the Moon in orbit around the Earth

moon phases

Half of the moon is always in sunlight. As the moon revolves around Earth the illuminated portion changes due to our viewing angle. As a result, the moon appears to change shape during the month creating the phases

waxing portion

to increase in size [lit portion] gradually

waning portion

to decrease in size [lit portion] gradually

moon cycle

The lunar phase cycle is 29.5 days. The Moon spends the extra 2.2 days "catching up" due to Earth traveling an additional 45 million miles in its revolution around the Sun

umbra

the fully shaded inner region of a shadow

penumbra

the partially shaded region of a shadow

solar eclipse

when the Sun is obscured by the moon. Occurs only during a new moon. The moon’s umbra has a width of about 269 km. Duration is up to 7 minutes as it passes over

lunar eclipse

when the moon appears darkened as it passes into the earth's shadow. Occurs during a full moon phase. The moon remains visible as a red-orange color due to some sunlight being refracted through Earth’s atmosphere into the umbra. Duration may last for up to 1.8 hours

why we only see one side of moon

One orbit is 27.3 days. The Moon rotates once every 27.3 days. Revolution = Rotation. Only one side of the moon is visible to Earth

tides

the cyclic rise and fall of sea levels caused by the Moon’s gravity, Sun’s gravity and Earth’s rotation. One tidal cycle is 12 hrs and 25 mins

spring tides

occur when the Sun and Moon are aligned [full and new moon] causing higher high tides

neap tide

occur when the Sun and Moon are acting on the earth in opposing direction