Rotation
• The spin of the Earth on its axis
– (rate of 15 /hr)
/hr)
• Earth is tilted at an angle of 23.5 degrees from
perpendicular
di l
• The Earth’s axis is always tilted in the same
direction throughout its orbit (parallelism
(parallelism))
Solar Time
• The
Th measurementt off time
ti based
b d on the
th apparentt
movement of the sun through the sky
• Solar Noon is the time of day when the sun is at its
highest altitude above the horizon
• Problem - solar noon does not occur at the same
y
((solar noon differs byy approx.
pp
1
time for everyone
minute for every 12 miles east/west of a specific
location))
• To make upp for this “problem”,
p
, time zones were
established (each 15 longitude wide – 1 hour of
rotation)
• Time zones begin at the Prime Meridian
• Every 15 degrees EAST is +1 hour, every 15
degrees
g
WEST is –1 hour
• Clock time is the average solar time
Revolution
• movement of the Earth around the sun in its elliptical
p
orbit
• One complete revolution is 365.25 days (1 year)
• In conjunction with AXIAL TILT, this causes a change
in the seasons
– no tilt of the axis = no seasonal changes
– Evidence of movement: Change in visible constellations
throughout the year
Solstices and Equinoxes
q
• SOLSTICE - extremes from the sun
– WINTER (perihelion) – 8 hours day/16 hr night
– SUMMER (aphelion) – 16 hours day/8 hr night
• EQUINOX – equal distances from the sun (equal
days/nights)
– Autumn (Vernal), Spring – 12 hours day/night
Nighttime
g
on the Artic Circle duringg the Summer. The sun never sets! It’s
always on the horizon.
Causes of Seasons
1.
2.
3.
4.
Earth’s revolution
Tilt of the Earth on its axis
Parallelism
More sunshine = more energy = warmer time
of year
y
5. Less sunshine = less energy = cooler time of
year