Transcript Seasons On Earth Notes

Warm-up: What causes our seasons?
• Finish Sun Video
• Seasons Notes
• Seasons Lab
• No Homework
Seasons On Earth Notes
Lesson 4
Earth’s Revolution and the Formation
of Seasons
• The movement of the Earth around the Sun is called
its revolution.
• The Earth’s tilted axis is fixed on Polaris, our North
Star.
• The Earth precesses, or wobbles, like a
spinning top wobbles. It takes the Earth
26,000 years to do a complete precession so it
points to different pole stars over the
centuries.
• During winter in the Northern Hemisphere (we are
tilted away from the sun) shadows point north at
solar noon.
• During summer in the Northern Hemisphere
shadows are shortest at solar noon.
• The long shadows in winter occur due to the
hemisphere being tilted away from the Sun.
The short shadows in summer occur due to
the hemisphere being tilted toward the Sun.
Sunrise and Sunset Times
• For 1,000’s of years astronomers have noticed
the Sun gradually changes its apparent
position in the sky over the course of the year.
It seems to move about 1 degree each day.
• That means the Sun rises about 1 minute later
or earlier each day.
Plane of the Ecliptic
• The plane along which Earth and most of the
planets orbit the sun is called the plane of the
ecliptic.
• The Sun’s apparent path in the sky is referred to as
the ecliptic.
• The ecliptic is tilted at about 23.5 degrees.
This tilt varies by 1 degree every 50,000 years.
• The change in the angle at which solar rays
reach the Earth at any time gives us the
Seasons.
• In the summer in Alaska, the sun barely sets. In the
winter the Sun barely rises. Near the equator, the
length of day hardly changes.
• There are two equinoxes (March 21 and September
21)
• The seasons on Earth are NOT related to the
distance the Earth is from the Sun.
• The North Star is NOT the brightest in the sky,
Sirius is the brightest after the sun.