Transcript SUN & SEASONS

SUN & SEASONS
Seasons mythology
Reasons for Seasons
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.
Persephone
Zeus
Demeter
Hades
Size of Stuff in the Sky
* Eye/brain gauges
angular size
UFO

Earth
soccer ball
 alone doesn’t give
you true size!
Moon & Sun

 = 0.5o
Earth
[Pinky test.]
Ack!
EQUINOXES &
SOLSTICES
Vernal
Equinox
Autumnal
Equinox
Winter &
Summer
Solstices
•
Vernal Equinox: March 21
• Autumnal Equinox: September 23
• Summer Solstice: June 21
• Winter Solstice: Dec 21
DAILY SOLAR MOTION
CHANGES 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 21
Sep 23
23.5o
90o – 41o
41o
Mar 21
Sep 23
[State College]
• Annual variation in motion of sun in sky results
from . . .
change in orientation of Earth
relative to sun:
Summer
Solstice
Winter
Solstice
Northern Winter Solstice
Northern Summer Solstice
[Demo, #3]
REASONS
FOR THE
SEASONS
• Temperature varies from season-to-season – Why?
- Sunlight more direct in summer (than in winter)
- More daylight hours in summer (and fewer in
winter)
Angled rays
Northern Winter Solstice
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!
Earth’s Orbit –
Exaggerated
July
January
Earth only ~ 3% closer in January than July