DEAN:
HEY THERE STAR GAZERS.
I'M DEAN REGAS, ASTRONOMER FOR THE CINCINNATI
OBSERVATORY.
JAMES:
AND I'M JAMES ALBURY, DIRECTOR OF THE KIKA
SILVA PLA PLANETARIUM IN GAINESVILLE,
FLORIDA.
WE'RE HERE TO HELP YOU FIND YOUR WAY AROUND
THE SKY TONIGHT.
DEAN:
THE WINTER SOLSTICE IS THURSDAY DECEMBER 21ST
AND SUN WORSHIPPERS CAN FINALLY REJOICE!
THIS IS THE TIME WHEN THE NORTHERN HEMISPHERE
EXPERIENCES THE SHORTEST DAYS AND LONGEST
NIGHTS.
JAMES:
WAIT A SECOND, REJOICE?
ON THE SHORTEST DAY?
WHAT'S TO CELEBRATE?
SOUND LIKE LOTS OF DARKNESS.
DEAN:
WELL, EVERY DAY AFTER DECEMBER 21ST, THE SUN
WILL GET HIGHER IN THE SKY AND STAY UP LONGER
ABOVE THE HORIZON.
THE SUN WILL STOP ITS SOUTHWARD MIGRATION
AND START HEADING NORTH AGAIN.
JAMES:
I WISH IT WOULD HURRY UP ALREADY, IT'S FREEZING
OUT HERE!
DEAN:
LET'S SHOW YOU THE REASON FOR THE SEASONS
JAMES:
THE CHANGING SEASONS ARE CAUSED BY ONE THING
- THE 23 AND A HALF DEGREE TILT OF
THE EARTH.
AS OUR PLANET ROTATES DAILY ON ITS AXIS, WE
ALSO REVOLVE AROUND THE SUN.
BUT OUR ROTATIONAL AXIS IS TILTED COMPARED
TO OUR ORBIT AROUND THE SUN, AND WE ALWAYS
KEEP THIS SLANTED VIEW.
DEAN:
WHEN WE, IN THE NORTHERN HEMISPHERE, ARE TILTED
MOST DIRECTLY TOWARD THE SUN WE SOAK UP SOLAR
ENERGY TO THE MAX.
THAT DAY IS CALLED THE SUMMER SOLSTICE AND
IT OCCURRED ON JUNE 21ST THIS YEAR.
AT THIS POINT THE SUN'S RAYS SHINE MOST DIRECTLY
ON THE NORTHERN HEMISPHERE.
WE GET MORE ENERGY PER SQUARE INCH, AND THUS
IT'S HOTTER.
JAMES:
NOW THE OPPOSITE OCCURS WHEN THE EARTH SWINGS
AROUND TO THE OPPOSITE SIDE OF THE SUN.
HERE, WE, IN THE NORTHERN HEMISPHERE, ARE
TILTED AWAY FROM THE SUN.
THE SUN'S RAYS FEEBLY STRIKE US AT A LOW ANGLE
SPREADING OUT THE SAME ENERGY OVER
A LARGER AREA.
EACH SQUARE INCH GETS A LOT LESS ENERGY THAN
IN SUMMER.
WE CALL THIS THE WINTER SOLSTICE AND THAT
OCCURS ON DECEMBER 21ST THIS YEAR.
DEAN:
THE SUN'S OUTPUT IS THE SAME ALL YEAR-ROUND.
BUT THE DIFFERENCE IN OUR SEASONS IS HOW MUCH
OF THAT ENERGY WE SOAK UP.
IT HAS NOTHING TO DO WITH HOW CLOSE OR FAR
WE ARE FROM THE SUN.
WE'RE CLOSEST TO THE SUN EVERY YEAR IN JANUARY
AND FARTHEST FROM THE SUN IN JULY.
SO THE DISTANCE DOESN T CAUSE THE DIFFERENCE
IN THE SEASONS
HEY JAMES, ARE YOU STAYING COOL?
JAMES:
THE SUN
IS BLASTING OFF MY HAIR!
DEAN:
OH YOU'RE DOING GREAT.
NOW LET'S SEE HOW OUR TILT AFFECTS THE VIEW
FROM DOWN ON EARTH.
DEAN:
SORRY ABOUT YOUR HAIR.
JAMES:
IT'S OKAY.
IT'LL GROW BACK.
DEAN:
HA!
JAMES:
ANYWAY, WE HAVE OUR SKIES SET TO DECEMBER
21ST JUST BEFORE SUNRISE.
LET'S TRACE THE PATH THAT THE SUN TAKES ACROSS
THE SKY ON THIS, THE SHORTEST DAY OF THE YEAR.
THE SUN WILL RISE SOUTH OF EAST, AND REACH
ITS HIGHEST POINT IN THE SOUTHERN SKY
AROUND NOON.
THEN THE SUN WILL SET SOUTH OF WEST.
DEAN:
FOR MOST OF THE COUNTRY YOU'LL GET ABOUT 9-10
HOURS OF DAYLIGHT ON THIS DAY.
THAT ALSO MEANS YOU'LL GET 14-15 HOURS OF
DARKNESS!
JAMES:
LET'S COMPARE THIS TO THE SPRING EQUINOX - NEXT
YEAR IT WILL BE ON MARCH 20TH.
NOW LET'S TRACE THE PATHWAY THAT THE SUN TAKES
ON THIS DAY.
THE SUN WILL RISE DUE EAST
REACH ITS HIGHEST POINT ABOVE THE SOUTHERN
HORIZON
AND THEN SET DUE WEST.
DEAN:
NOTICE HOW THE SUN WENT HIGHER IN THE SKY
THAN IT DID IN DECEMBER.
THE HIGHER THE SUN,
THE MORE DIRECT ENERGY WE GET.
JAMES:
AND LOOK AT HOW MUCH LONGER THE SUN WAS IN
THE SKY!
12 HOURS OF DAYLIGHT, AND 12 HOURS OF DARKNESS.
EQUAL DAY, EQUAL NIGHT.
THATS WHY THEY CALL IT THE EQUINOX.
DEAN:
WHAT ABOUT THE SUMMER SOLSTICE?
NOW OUR SKY IS SET TO JUNE 21ST, AND WE CAN
WATCH THE SUN RISE NORTH OF EAST
GO VERY HIGH IN THE SOUTH
AND SET NORTH OF WEST.
JAMES:
THE SUN WENT HIGHER STILL IN THE SKY.
AND THE HOURS OF DAYLIGHT REACH A WHOPPING
14-15 HOURS FOR MOST OF THE U.S WITH ONLY
9-10 HOURS
OF DARKNESS.
DEAN:
AND ALL OF THIS IS CAUSED BY THE 23 AND
A HALF DEGREE TILT OF THE EARTH.
DEAN:
SO ON DECEMBER 21ST WATCH THIS EXTREME SOUTHERLY
SUNSET.
JAMES:
AND IN SIX MORE MONTHS IT WILL REACH THE OTHER
EXTREME: NORTHERNMOST SUNSET ON THE SUMMER
SOLSTICE ON JUNE 21ST.
DEAN:
SOAK UP THE SOLSTICE SUN - BECAUSE THE LONGER
DAYS ARE RETURNING AND SUMMER IS COMING SLOWLY
BOTH:
KEEP LOOKING UP!