Earth in Space
What causes day and night?
• ROTATION: Earth
spinning on its axis is
called its rotation and it
causes day and night.
• It takes 24 hours or 1 day
for Earth to rotate once
on its axis.
Day and Night
• The Earth continuously
rotates to the east
which is why the sun
appears to set in the
west.
• It is nighttime on the
side where the Earth is
not facing the Sun;
daytime where the Earth
is facing the Sun.
What causes years?
• REVOLUTION: Earth traveling around
(orbiting) the Sun is called revolution.
• It takes 365.25 days for Earth to revolve
once around the Sun.
What causes
Seasons?
• Two things cause Earth to have
seasons
1. Revolution of Earth around the Sun
2. The TILT of Earth’s axis as it
revolves around the Sun.
 Earth is tilted 23.5° on its axis.
What causes
Seasons?
• When the North Pole is tilted TOWARDS
the Sun the Northern Hemisphere is
experiencing Summer.
• When the North Pole is tilted AWAY from
the Sun the Northern Hemisphere is
experiencing Winter.
Solstices
• Summer Solstice – June 21 or 22
▫ 1st Day of Summer
▫ Longest “Day” of the year
 The most hours of daytime
 The sun is directly over the Tropic of Cancer.
• Winter Solstice – December 21 or 22
▫ 1st Day of Winter
▫ Longest “Night” of the year
 The most hours of nighttime
 The sun is directly over the Tropic of Capricorn.
Equinox
• Spring Equinox – March 20 or 21
▫ 1st Day of Spring
▫ EQUAL amount of daytime and nighttime
 The sun is directly over the Equator.
• Fall Equinox – September 22 or 23
▫ 1st Day of Fall
▫ EQUAL amount of daytime and nighttime
 The sun is directly over the Equator.