Download CH .19 Earth Moon Sun I. Astronomy – study of stars, planets, and

CH .19 Earth Moon Sun
I. Astronomy – study of stars, planets, and all other things in space
A. Days and Years
1. rotation – earth spinning on its axis
a. spins once each day or 24 hrs.
b. when you point toward sun it’s day, away from sun at night
2. revolution – going around the sun
a. Earth goes around sun once per year or 365.25 days
1) the 0.25 days causes the 29th day in February each leap
year
b. orbit – path an object takes around another object
1) Earth’s orbit is slightly oval shaped or elliptical
B. Seasons – caused by Earth’s tilted axis
1. tilt is 23.5o from vertical
2. where sun hits more directly (equator) it’s hotter
3. at poles, sun hits at an angle, so sun rays are less compact
4. (diagram)
5. Summer – happens when our part of the Earth tilts toward the sun
a. causes longer days
b. more direct sun is more concentrated, so heats more
1) also causes sun burn better
c. June 21 – longest day of year in northern hemisphere, shortest
in southern
6. Winter – happens when our part of the planet tilted away from sun
a. causes shorter days
b. sunlight is least direct – least intense
c. Dec. 21 – shortest day of the year in north, longest in south
hemisphere
7. Solstice – longest and shortest day of the year 6/21, and 12/21
8. Spring and Fall – sun at medium intensity and day length
a. equinox – sun directly above equator at noon, 12 hour day
b. vernal equinox – first day of spring – 3/21
c. autumnal equinox – first day of fall – 9/21
II. Phases, Eclipses, and Tides
A. The Moon – closest object to Earth in space
1. revolves around the Earth in 27.3 days
a. elliptical orbit
2, also rotates on its axis once every 27.3 days
a. keeps the same side always pointing at the Earth
B. Moon Phases – different moon shapes
1. determined by amount of sunlit moon surface pointing toward the Earth
2. new moon – dark side of moon pointing toward Earth
3. waxing crescent – sickle shaped and getting bigger
4. first quarter – half moon – waxing
5. waxing gibbous – between half and full and getting bigger
6. full moon – entire sunlit side of moon pointing toward Earth
7. waning gibbous – between full and quarter and getting smaller
8. 3rd quarter – half moon and waning
9. waning crescent – sickle shaped and getting smaller
10, entire cycle takes about 29.5 days
C. Eclipses – shadow of one object on another
1. solar eclipse – moon shadow on Earth – moon between Earth and Sun
a. total solar eclipse – completely dark part of moon shadow
(umbra) is on Earth
1) sky dark + can see stars – all sunlight blocked
b. partial solar eclipse – only part of the sun blocked by moon
1) penumbra – not fully darkened part of shadow
c. since shadow is cone shaped and sun is far away, only small
part of Earth sees solar eclipses
2. lunar eclipses – Earth blocks sunlight from full moon
a. all of Earth experiencing night can see lunar eclipse –
1) more common than solar eclipses
b. not perfect line-up creates partial lunar eclipse
D. Tides – rising and falling ocean levels
1. caused by moon gravity on part of Earth lined up with the moon
2. two high tides per day and 2 low tides per day
a. each high tide is about 12.5 hrs. apart
III. Earth’s Moon
A. Origin
1. Collision Theory – When solar system was forming, a planet a little
smaller than Earth collided with Earth
a. the 2 planets combined to make Earth larger.
b. a piece of early Earth broke off in collision and became the
moon
2. size of the moon – about ¼ Earth’s size
3. density – bout the same as Earth’s crust
a. the crust is the outer layer of land on Earth
B. Observing the Moon
1. 1609 – first telescope – Galileo
a. can see moon’s features – craters, Highlands, maria
2. craters – made by meteor impacts
3. maria – dark areas – once thought to be oceans, now known to be
made from lava flows
4. space craft have found ice near north pole of moon