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Transcript
Why do we have Days,
Seasons, and Years?
What on Earth is a day?
• “The time it takes for the Earth (or any planet/moon)
to make one complete rotation.”
• 24 hours
• Part of each 24-hour day is lighted (daytime), part is
dark (night).
• The length of daytime and nighttime varies
depending on how the Earth is tilted.
Earth Orbit (Revolution)
The Earth orbits (revolves) around the sun once every 365 days. This is
where our year comes from. In fact, for every planet a year is the time it
takes to orbit it’s star one time. Our orbit is not a perfect circle. It is an
ellipse. When do you think we are closer to the sun - in our summer our
our winter?
Summer: 152,000,000 Km Winter: 147,000,000 Km
Earth’s Tilt
Reason for
the
Seasons:
The earth’s axis
is always tilted
at 23.5. When
a hemi-sphere
tilts towards the
sun it gets more
direct sunlight so
it experiences
warmer
temperatures
(summer). The
opposite is true
when the tilt is
away from the
sun (winter).
http://www.windows.ucar.edu/earth/climate/images/seasons_lg.gif
Spring - March 21st
• Spring Equinox
• First day of Spring
• Equal length of daytime
& nighttime
• Sun directly over
equator
• Fall in southern
hemisphere
North
Summer - June 21st
• Summer Solstice
• First day of Summer
North
• Longest daytime in N
hemisphere
• Longest nighttime in S
hemisphere
• Sun over Tropic of Cancer
• Winter in southern hemisphere.
• 24 hours of daytime above the Artic
Circle & 24 hours of nighttime below the
Antarctic Circle.
Fall - September 22
• Fall/Autumnal Equinox
North
• First day of Fall
• Equal length of daytime and
nighttime
• Sun directly over equator
• Springtime in southern
hemisphere.
Winter - December 21
• Winter Solstice
North
• First day of Winter
• Longest nighttime in N
hemisphere
• Longest daytime in S
hemisphere
• Sun over Tropic of
Capricorn
• 24 hours of nighttime above the Artic
Circle & 24 hours of daytime below the •
Antarctic Circle.
Summer in southern
hemisphere