DEAN: WELCOME TO STAR GAZERS!
I'M DEAN REGAS, ASTRONOMER FROM THE CINCINATTI OBSERVATORY.
JAMES: AND I'M JAMES ALBURY, DIRECTOR OF THE KIKA SILVA PLA PLANETARIUM IN GAINESVILLE,
FLORIDA.
LAST SUMMER, VENUS AND JUPITER LINED UP IN SUCH A WAY THAT THEY PERFORMED A SUPER-SCOOTCHIE
IN THE EVENING SKY, AS VIEWED FROM EARTH.
DEAN: THE OFFICIAL ASTRONOMICAL TERM FOR A PLANETARY SCOOTCHIE IS A CONJUNCTION AND IF
YOU HAPPEN TO BE A FAN OF PLANETARY CONJUNCTIONS LIKE JAMES, YOU'RE GOING TO BE REALLY HAPPY
ON AUGUST 27TH.
JAMES: THAT'S RIGHT DEAN!
VENUS IS BACK IN THE EVENING SKY AND IT WILL HAVE ANOTHER SUPER-DUPER CLOSE RENDEZVOUS
WITH JUPITER.
THIS PAIRING WILL BE SO CLOSE THAT JUPITER AND VENUS WILL BE LESS THAN A FULL MOON WIDTH
APART RIGHT AFTER SUNSET.
DEAN: WHAT ARE WE TALKING ABOUT?, AND HOW DOES IT ALL WORK?
LET'S SHOW YOU!
JAMES: AS MANY OF YOU KNOW, THE PLANETS ORBIT THE SUN IN NESTED ELLIPSES.
WHEN WE VIEW THE SOLAR SYSTEM FROM ABOVE, THE PLANETS LOOK LIKE RUNNERS ON A RACE TRACK,
WITH EACH PLANET IN A DIFFERENT LANE.
MERCURY BEING THE CLOSEST PLANET TO THE SUN; THEN VENUS, THEN EARTH AND THEN MARS AND SO
ON.
DEAN: AS WE TRAVEL AROUND THE SUN, WE'RE ALL TRAVELING AT DIFFERENT SPEEDS.
THE ASTRONOMER JOHANNES KEPLER NOTICED THAT PLANETS CLOSER TO THE SUN TRAVEL FASTER THAN
THOSE FARTHER AWAY.
FOR EXAMPLE, IT TAKES MERCURY ONLY 88 EARTH DAYS TO ORBIT THE SUN, MOVING AT A BRISK 106,000
MILES PER HOUR.
VENUS, BY COMPARISON TAKES 225 DAYS TO ORBIT THE SUN, MOVING AT A SLOWER 78,000 MILES PER
HOUR.
JAMES: EARTH TAKES ROUGHLY 365 DAYS TO ORBIT THE SUN, TRAVELING APPROXIMATELY 66,000 MILES
PER HOUR, MEANWHILE MARS TAKES ALMOST TWO YEARS TO ORBIT THE SUN.
ON AVERAGE, MARS IS MOVING AT ABOUT 54,000 MILES PER HOUR, DRAGGING ITS TWO MOONS PHOBOS
AND DEIMOS ALONG WITH IT.
DEAN: AS WE GET FURTHER FROM THE SUN, KEPLER'S OBSERVATIONS OF PLANETARY MOTION STILL HOLD
TRUE.
JAMES: JUPITER TAKES ALMOST 12 YEARS TO ORBIT THE SUN, TRAVELING AT A POKEY 29,000 MILES
PER HOUR.
JUPITER WAS AT ITS CLOSEST APPROACH TO EARTH THIS YEAR, BACK IN EARLY FEBRUARY.
SINCE THAT TIME, EARTH HAS TRAVELED OVER 237 MILLION MILES, LEAVING JUPITER BEHIND.
DEAN: VENUS, WHICH IS TRAVELING FASTER THAN THE EARTH, HAS ROUNDED THE SUN AND IS NOW
EMERGING FROM BEHIND THE SUN.
AS IT TRAVELS, IT WILL APPEAR ALONG OUR LINE OF SIGHT WITH RESPECT TO JUPITER.
JAMES: AND THIS IS WHAT CAUSES A CONJUNCTION.
NOW, YOU'RE PROBABLY ASKING YOURSELF, WHY DON'T VENUS AND JUPITER GET SUPER CLOSE EVERY
YEAR?
LET'S SHOW YOU!
DEAN: NOT ONLY ARE THE ORBITS OF PLANETS NESTED ELLIPSES, THEY'RE ALSO INCLINED TO EACH OTHER.
IN OTHER WORDS, THE ORBITS, ALTHOUGH THEY APPEAR FLAT, ALL VARY IN THEIR TILT, SLIGHTLY.
JAMES: WE CALL THE TILT OF A PLANET'S ORBIT, ITS ORBITAL INCLINATION.
IT'S THE VARIATION IN EACH PLANET'S ORBITAL INCLINATION AND THE TIMING OF PLANETARY PASSAGES,
THAT MAKES SOME CONJUNCTIONS CLOSER THAN OTHERS.
DEAN: VENUS AND JUPITER USUALLY HAVE A CONJUNCTION EVERY YEAR, AND THEY CAN PUT ON QUITE A SHOW.
DEAN: FOR EXAMPLE, IN JULY 2012, VENUS AND JUPITER HAD A CLOSE CONJUNCTION IN THE CONSTELLATION
TAURUS THE BULL, JUST BEFORE SUNRISE ON JULY 15TH.
JAMES: THEN, IN MAY 2013, VENUS AND JUPITER HAD AN EVEN CLOSER CONJUNCTION AND WERE JOINED
BY MERCURY ON THE EVENING OF MAY 28TH.
DEAN: THEN, IN AUGUST 2014, VENUS AND JUPITER HAD AN IMPRESSIVELY CLOSE CONJUNCTION IN THE
PRE-DAWN SKY ON AUGUST 18TH.
JAMES: IF YOU NOTICE, THERE IS A PATTERN HERE.
EACH YEAR, WE ALTERNATE BETWEEN MORNING CONJUNCTIONS AND EVENING CONJUNCTIONS.
THAT'S BECAUSE EVERY 9 MONTHS, VENUS ALTERNATES BETWEEN BEING ON THE EASTERN SIDE OF THE SUN,
WHERE IT'S VISIBLE JUST AFTER SUNSET AND WE CALL IT THE EVENING STAR.
DEAN: AND THEN VENUS PASSES THE EARTH, IS CAUGHT IN THE GLARE OF THE SUN FOR ABOUT A
WEEK, AND THEN REAPPEARS ON THE WESTERN SIDE OF THE SUN, WHERE IT'S VISIBLE BEFORE THE
SUN RISES.
IN THIS POSITION, WE CALL VENUS, THE MORNING STAR.
JAMES: SO, AS YOU PROBABLY GUESSED, VENUS IS CURRENTLY IN ITS EVENING STAR POSITION,
AND AFTER SUNSET ON AUGUST 27TH, WE'LL EXPERIENCE ONE OF THE CLOSEST VENUS-JUPITER CONJUNCTIONS
HUMANS HAVE SEEN IN A LONG TIME.
SO MARK YOUR CALENDARS…
DEAN: AND IF YOU HAVE CLEAR SKIES YOU CAN SEE IT FOR YOURSELF.
BOTH: KEEP LOOKING UP!