summer solstice june 21, 2011 - tanglewood...
TRANSCRIPT
Tanglewood Astronomy Club
SUMMER SOLSTICE
June 21, 2011
Solstices and the Sun
• From the latin word solstitium, meaning
sun stands still.
• During the summer and winter solstices the
path of the sun above us does not change
much day to day.
The Solstices – Earth and our Sun
sunrise sunset hours
SUMMER SOLSTICE June 21 5:31 8:47 ~15
Fall Equinox Sept 23 6:55 7:03 ~12
WINTER SOLSTICE Dec 22 7:33 4:39 ~ 9
Spring Equinox Mar 20 7:10 7:20 ~12
• Summer Solstice – in Anchorage Alaska there is
functional daylight all 24 hours.
Gosek (Germany) Sun circle
Concentric ditches and
(reconstructed) wooden fence
with openings that mark the
sunrise and sunset on the
Winter Solstice
Pottery at site indicates circle may
have been built as far back as
7000 years ago. Wikipedia
indicates that this site is the
earliest known solar observatory.
Stonehenge• On summer
solstice sun rises beside the heel stone and would have hit the alter stone.
• Version seen today built ~ 3500 years ago
AP photo
Lefteris
Pitarakkis
Chaco Canyon (Pueblo) Sun Dagger
Unfortunately visitors traffic at the site led
to increased water erosion and the stone
monoliths slipped out of alignment in
1989.
Besides tracking the sun cycle it
appears it also tracked an 18.5 year
lunar cycle.
Built over 700 years ago.
Modern Sun Wheel – UMASS Amherst
Earth’s Orbit about the Sun
~ 91 million miles ~ 95 million milesWinter
Solstice
Dec 22
Summer
Solstice
today
• Earth orbits the Sun in an ellipse
• Earth is actually closer to the Sun during our winter
• But, since the orbit is very close to a circle, not much difference
• About 7% difference in sunlight density from summer to winter
Earth is tilted as it orbits the Sun
• Earth is tilted ~ 24 degrees see globe
• This tilt is the MAIN cause of the summer and winter seasons
• During our summer, the sun is roughly over Palm Beach, Florida
• During our winter, the sun is roughly over Rio de Janeiro, Brazil
• The density of the sunlight is spread over a much larger area around us during the winter, lowering the amount of sun power.
Solstices and sunlight
• Neglecting absorption of sunlight in air, a
piece of notebook paper in Elmira gets:
• 27 Watts of sunlight on the summer solstice
• Only 9 watts of sunlight at the winter solstice
So we get only 1/3 of the sunlight on Dec 21
compared to June 21.
What is above us right now ? (If the sun disappeared)
SUN
ORION
Winter
Constellation
Saturn
Jupiter
Mars
Venus
Mercury
FACING SOUTH TONIGHT, ~ 10:30PM
Antares is a Red
SuperGiant Star,
about 15th
brightest in the
sky to eye