Earth, Moon, and Sun
Text Notes (pg. 11-12) – “What Causes Seasons?”
 Earth’s weather patterns change in a regular, predictable cycle.
o 4 main divisions of the year
 Spring
 Summer
 Autumn
 Winter
 Seasons are not caused by elliptical orbit
 Earth’s axis is tilted 23.5 degrees
o Axial tilt stays the same, but as earth travels around the sun, it makes North and
South Poles point toward or away from the sun at different times of year.
Spring
Summer
Winter
North Pole
pointed toward
the sun
North Pole
pointed away
from sun
Between
summer and
winter
Between
winter and
summer
June 20th or
21st to
September
22nd or 23rd
December 21st
or 22nd to
March 20th or
21st
Daylight hours
decrease
Daylight hours
increase
Weather gets
colder
Weather gets
warmer
Warmer
weather b/c...
Colder
weather b/c...
- Sun's light
strikes directly
which creates
more solar
energy which is
concentrated in
smaller areas
- Sun's light is
spread out
over a larger
area due to
angle of
hemisphere
which is tilted
away from
sun.
- Receives more
hours of
daylight
-Receives
fewer hours of
daylight
Autumn
Solstices
 Equator is at zero degrees latitude
 Because Earth is tilted on its axis, the Sun’s position relative to the equator is always
changing.
 Twice a year a solstice occurs
o Summer Solstice
 June 20th or 21st
 Northern hemisphere is tilted toward the Sun.
 Sun appears overhead at 23.5 degrees north of the equator (Tropic of
Cancer)
 1st day of summer in Northern Hemisphere
 Longest period of daylight
 Southern Hemisphere is tilted away from Sun and its their 1st day of winter.
o Winter Solstice
 December 21st or 22nd
 Northern Hemisphere is tilted away from the Sun
 Sun appears overhead at 23.5 degrees south of the equator (Tropic of
Capricorn)
 1st day of winter in Northern Hemisphere
 Shortest period of daylight
 Southern Hemisphere has their longest period of daylight and its their 1st
day of summer.
Equinoxes
 Sun’s rays strike the equator directly
 Day (12 hours) and night (12 hours) are of equal length in both hemispheres
 From the Latin word for “equal night”
o Vernal Equinox
 March 20th or 21st
 Beginning of spring in Northern Hemisphere
o Autumnal Equinox
 September 22nd or 23rd
 Beginning of autumn in Northern Hemisphere