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.