TheSolstice Bash
Reasons for the Seasons
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?
The Heliocentric View
The Geocentri
c View:
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?
Changing Seasons
North South
East
West
WinterSolstice
SummerSolstice
Fall EquinoxSpring Equinox
Insolation
• Why is it colder in Winter?• Not just because the days are shorter!• When the Sun is low in the sky, its flux
is more spread out.