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sunwatching
• How does the Sun’s path across the sky change from season to season?– When is the day longest?– When is the day shortest?
• Does the Sun always rise and set in the same place on the horizon?
• Does it always rise to the same height in the sky?
Morning on Earth
• The Sun rises on the eastern horizon.
• In the summer, the Sun rises to the north of east.
• In the winter, the Sun rises to the south of east.
Noon
• Noon is when the Sun reaches its highest point in the sky.
• In summer, this is higher in the sky than in winter.
• In Ithaca, is the Sun ever directly overhead in summertime?
Sunset
• Sunset is symmetrical with sunrise.
• If the Sun rises 10˚ north of east, it will set 10˚ north of west.
• Can we create a simple picture that shows how the Sun moves through the sky at different times of the year?
CelestialSphere
Geocentric View from the Ground
Horizon
North South
East
West
CelestialNorth Pole
CelestialEquator
The Ecliptic Plane
• In the heliocentric picture, the ecliptic is the plane of the Earth’s orbit.
• What is the ecliptic in the geocentric picture?
TheEcliptic on the Celestial Sphere
• As the celestial sphere whirls once per day, the Sun creeps along the ecliptic.
• How will this affect the Sun’s path through the sky?