sun & seasons

SUN & SEASONS

Seasons mythology

Reasons for Seasons

Zeus HadesPersephone

Persephone was the Greek goddess of the Underworld and the wife of Hades. Hades fell in love with her after seeing her picking flowers in a plain in Sicily. He decided at once to abduct her and carry her off to the Underworld. Demeter, sister of Zeus, was the mother of Persephone. After Persephone's abduction, Demeter wandered the world in search of her. Finally she learned of her daughter's fate, and pleaded with Zeus, to obtain the release of Persephone from the dark kingdom of the Underworld. He consented, providing that she had not eaten anything during her stay in the lower world. Unfortunately, Persephone had eaten some seeds of a pomegranate which Hades had offered to her. After much crying and sadness, Zeus allowed a compromise, whereby Persephone was allowed to spend half of each year in the light of day, on Earth with her mother, and the other half in the underworld, where she reigned as Queen of the Underworld alongside her husband the god Pluto. During the half year with her mother, spring and summer cover the Earth in warmth, flowers bloom, fruit is on the trees, and the birds raise their young. During autumn and winter, the Earth is in the grip of icy cold. Flowers die, the trees are barren, and birds disappear from their nests. This legend, therefore, relates the mythological creation of the seasons.

Demeter

UFO

Size of Stuff in the Sky

Earth

* Eye/brain gauges angular size

soccer ball

alone doesn’t giveyou true size!

Moon & Sun

Earth

= 0.5o

Ack![Pinky test.]

EQUINOXES &SOLSTICES

VernalEquinox

AutumnalEquinox

Winter &SummerSolstices

• Vernal Equinox: March 21

• Autumnal Equinox: September 23

• Summer Solstice: June 21

• Winter Solstice: Dec 21

DAILY SOLAR MOTIONCHANGES WITH SEASONS

• Motion N/S of Celestial Equator

> Rising/setting points vary> Noon altitude varies> Duration of daylight varies

• Mar 21 – Sep 23: sun north of celestial equator

sun above horizon > 12 hrs

• Sep 23 – Mar 21: sun south of celestial equator

sun above horizon < 12 hrs

• Sep 23 & Mar 21: sun on celestial equator sun above/below horizon 12 hrs

41o

Mar 21Sep 23

41o

Mar 21Sep 23

90o – 41o

23.5o

[State College]

• Annual variation in motion of sun in sky results from . . .

change in orientation of Earth relative to sun:

SummerSolstice

WinterSolstice

Northern Winter Solstice

Northern Summer Solstice [Demo, #3]

REASONSFOR THESEASONS

• Temperature varies from season-to-season – Why?

- Sunlight more direct in summer (than in winter)

- More daylight hours in summer (and fewer in winter)

Northern Winter Solstice

Angled rays

Northern Summer Solstice

Summer Sun

Winter Sun

• No significant temperature change due to change in Earth-sun distance, angle has more to do with it

- e.g., N. hemisphere not much closer to sun than S. hemisphere in summer

- Earth actually closest to sun in January!

JanuaryJuly

Earth’s Orbit – Exaggerated

Earth only ~ 3% closer in January than July