SEASONS
THE REASON FOR SEASONS
• THE EARTH REVOLVES AROUND THE SUN IN A PATH THAT REPEATS ITSELF EVERY YEAR OR 365
DAYS.
• THIS PATH IS CALLED AN ORBIT.
• IN THE PAST, SOME PEOPLE BELIEVES THE EARTH WAS THE CENTER OF OUR SOLAR SYSTEM
INSTEAD OF THE SUN. THE FACT THAT THE EARTH ORBITS OR REVOLVES AROUND THE SUN
WAS PROVEN BY GALILEO.
• THE EARTH’S ORBIT IS SLIGHTLY ELLIPTIC (MORE OVAL THAN CIRCULAR.)
• THE EARTH HAS AN IMAGINARY POLE RUNNING THROUGH ITS CENTER CALLED AN AXIS.
• THE EARTH'S AXIS IS NOT STRAIGHT UP AND DOWN. IT IS TILTED AT AN ANGLE OF 23.5
DEGREES.
• THIS TILT IS WHAT CAUSES THE SEASONS.
• IF THE EARTH WEREN’T TILTED, WE WOULD HAVE NO SEASONS, BUT THE TILT CREATES SPRING,
SUMMER, FALL, AND WINTER.
• MISCONCEPTION!!!!! SOME PEOPLE THINK THE REASONS WE HAVE SEASONS IS BECAUSE THE
EARTH IS CLOSER TO THE SUN. WRONG!!!!!!! IN FACT, THE EARTH IS CLOSEST TO THE SUN IN
THE WINTER.
• EXAMPLE:
• STAND 30 FT. AWAY FROM A FIREPLACE.
• TAKE ONE SMALL STEP CLOSER.
• WILL YOU FEEL ANY WARMER? NO
• WHY? THE DISTANCE BETWEEN THE EARTH AND SUN IS SO LARGE, A SMALL CHANGE DOES NOT
AFFECT OUR WARMTH. IT IS THE TILT!
• THE EARTH EXPERIENCES SEASONS BECAUSE OF TWO FACTS:
1. EARTH REVOLVES AROUND THE SUN EVERY YEAR.
2. EARTH IS TILTED.
3. LETS EXPLORE WHY THE TILT IS SO IMPORTANT…. IT CREATES TWO EFFECTS..
TWO EFFECTS
1.
AMOUNT OF DAYLIGHT (HOW LONG THE SUN STAYS IN THE SKY)
2.
DIRECT VS. INDIRECT LIGHT (ANGLE OF THE SUN ABOVE THE HORIZON)
AMOUNT OF DAYLIGHT
• THE LENGTH OF THE DAY CHANGES WITH EACH SEASON.
• THINK ABOUT IT….
• WHEN DO YOU WATCH FIREWORKS IN THE SUMMER?
• USUALLY AFTER 9 P.M. OR 10 P.M.
• WHEN DO YOU TURN ON CHRISTMAS LIGHTS IN WINTER?
• USUALLY AFTER 5 P.M.
• COMPLETE THE TABLE
• CHART THE SUN FOR EACH SEASON BELOW
• IN THE SUMMER, THE SUN IS HIGH OVERHEAD AND THE DAYS ARE LONGER. THIS GIVES THE
SUN PLENTY OF TIME TO HEAT THE EARTH.
• IN THE WINTER, THE SUN IS LOW OVERHEAD AND THE DAYS ARE SHORTER. THIS GIVES THE
SUN LITTLE TIME TO HEAT THE EARTH.
• WHEN THE NORTHERN HEMISPHERE IS TILTED TOWARD THE SUN IN JUNE, THE
SUN APPEARS HIGH IN THE SKY. THE ANGLE OF THE SUNLIGHT HITTING EARTH
IS HIGH. THIS MEANS THAT THE NORTHERN HEMISPHERE RECEIVES MORE
ENERGY AND MORE HEAT FROM THE SUN.
• WHEN THE NORTHERN HEMISPHERE IS TILTED AWAY FROM THE SUN IN
DECEMBER, THE SUN APPEARS LOW IN THE SKY. THE ANGLE OF THE SUNLIGHT
HITTING EARTH IS LOW. THIS MEANS THAT THE NORTHERN HEMISPHERE
RECEIVES LITTLEE ENERGY AND LITTLE HEAT FROM THE SUN.
• THIS CHART IS FOR UTAH AND OTHER LOCATIONS IN THE NORTHERN
HEMISPHERE. HOW WOULD I BE DIFFERENT FOR THE SOUTHERN HEMISPHERE?
THEY ARE OPPOSITE!
• AS THE EARTH REVOLVES AROUND THE SUN, FOUR IMPORTANT DATES OCCUR:
• SUMMER SOLSTICE= JUNE 21
• WINTER SOLSTICE= DECEMBER 21
• FALL OR AUTUMNAL EQUINOX= SEPTEMBER 21
• SPRING EQUINOX= MARCH 21
• SOLSTICE: SUN STANDING STILL
• EQUINOX: EQUAL NIGHT
DIRECT AND INDIRECT LIGHT
• SINCE THE EARTH IS ROUND, THE RAYS FROM THE SUN DO NOT STRIKE THE SURFACE THE SAME
WAY.
• CONSIDER THE FOLLOWING DIAGRAM, WHICH SURFACE DO YOU THINK WILL BE THE
HOTTEST? COOLEST? WHY?
• DRAW THE RAYS OF LIGHT COMING FROM EACH FLASHLIGHT TO SHOW THE RESULTS.
• A. DIRECT LIGHT ALL BEAMS SAME LENGTH. SHORT, DIRECT BEAMS. WARMEST TEMP.
• B. SOME RAYS ARE SHORT. SOME RAYS ARE LONG.
• C. INDIRECT LIGHT GREAT VARIETY OF LENGTH. COOLEST TEMP.
• APPLY THIS CONCEPT TO THE CURVES SURFACE OF THE EARTH. FILL IN THE RAYS OF LIGHT FROM
THE SUN. WHICH AREAS ARE THE WARMEST? COOLEST?
• THE MOST INDIRECT SUNLIGHT IS AT THE NORTH AND SOUTH POLES. THAT IS WHY THEY ARE
ALWAYS COLD.
• THE MOST DIRECT SUNLIGHT IS AT THE EQUATOR. THAT IS WHY IT IS ALWAYS HOT.
• IN THIS ILLUSTRATION, THE EARTH AXIS IS LEANING TOWARD THE SUN, SO THE MOST DIRECT RAYS
ARE STRIKING THE NORTHERN HEMISPHERE CAUSING IT TO EXPERIENCE SUMMER.
• THE MOST INDIRECT RAYS ARE STRIKING THE SOUTHERN HEMISPHERE CAUSING IT TO EXPERIENCE
WINTER.