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CEPHEUS!

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JAMES: 
WELCOME TO STAR GAZERS.

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I'M JAMES ALBURY, DIRECTOR OF THE KIKA SILVA 
PLA PLANETARIUM IN GAINESVILLE FLORIDA.

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DEAN: 
AND I'M DEAN REGAS, ASTRONOMER FROM THE CINCINNATI

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OBSERVATORY.

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WE RE HERE TO HELP YOU FIND YOUR WAY AROUND 
THE SKY.

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THIS WEEK, WE RE GOING TO TALK ABOUT A CONSTELLATION 
THAT S PART OF AN ANCIENT CELESTIAL STORY.

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JAMES: 
AND MORE EXCITINGLY, ONE OF ITS STARS HELPED

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ASTRONOMERS DETERMINE THE SIZE AND SHAPE OF 
OUR OWN GALAXY AND THE DISTANCES TO NEARBY

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GALAXIES.

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WONDERING WHAT WE RE TALKING ABOUT?

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LET S SHOW YOU!

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JAMES: 
OK, WE HAVE OUR SKIES SET FOR AN HOUR AFTER

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SUNSET, ANY NIGHT THIS WEEK, FACING NORTH.

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OFF TO THE NORTHEAST YOU LL SEE THE FAMILIAR 
W-SHAPED PATTERN OF CASSIOPEIA THE QUEEN.

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THE STARS THAT MARK THIS CONSTELLATION, STARTING 
FROM THE TOP DOWN ARE CAPH, SHEDAR, TSIH,

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RUCHBAH 
AND SEGIN.

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DEAN: 
IF YOU DRAW A STRAIGHT LINE FROM SHEDAR

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TO CAPH AND 
KEEP ON GOING,

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YOU LL RUN SMACK DAB INTO A CONSTELLATION 
THAT LOOKS LIKE AN

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UPSIDE-DOWN HOUSE.

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THIS IS CEPHEUS THE KING.

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CEPHEUS WAS THE HUSBAND OF CASSIOPEIA AND 
FATHER OF ANDROMEDA.

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JAMES: 
THE BRIGHTEST STAR IN CEPHEUS IS TOWARD THE

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UPPER LEFT AT THIS TIME OF NIGHT IN OCTOBER.

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THAT STAR S NAME IS ALDERAMIN AND IT S 
49 LIGHT YEARS

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AWAY FROM US.

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SINCE IT IS THE BRIGHTEST STAR 
IN CEPHEUS,

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IT IS NAMED ALPHA CEPHEII.

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DEAN: 
ALDERAMIN LIES VERY CLOSE TO A REGION OF THE

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NORTHERN SKY CALLED THE 
PRECESSION CIRCLE.

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OVER A PERIOD OF 
26,000 YEARS,

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EARTH S ROTATIONAL AXIS PASSES THROUGH SEVERAL 
CONSTELLATIONS, TRACING A GIANT CIRCLE IN

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THE SKY.

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RIGHT NOW, OUR ROTATIONAL AXIS IS POINTING 
TOWARD POLARIS; OUR CURRENT NORTH STAR.

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HOWEVER, IN 7500 AD, ALDERAMIN WILL BE OUR 
NORTH STAR.

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JAMES: 
I'LL BE SURE TO MARK THAT ON MY CALENDAR.

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JAMES: 
TRAVELING COUNTER CLOCKWISE FROM ALDERAMIN,

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WE HAVE ALFIRK, ALSO KNOWN AS BETA CEPHEII.

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ALFIRK IS A MULTIPLE STAR SYSTEM APPROXIMATELY 
690 LIGHT YEARS FROM EARTH.

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ALFIRK WILL BE OUR NORTH STAR BETWEEN 5200 
AD AND 7500 AD.

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DEAN: 
THE NEXT STAR IN CEPHEUS IS ERRAI;

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ALSO KNOWN AS GAMMA CEPHEII.

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ERRAI MARKS THE POINT ON THE ROOF OF THIS 
HOUSE-SHAPED CONSTELLATION AND IS

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A BINARY STAR SYSTEM APPROXIMATELY 45 LIGHT 
YEARS AWAY.

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ERRAI WILL BECOME OUR NORTH STAR IN LESS THAN 
A THOUSAND YEARS,

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AND IT WILL RETAIN THE TITLE OF NORTH STAR 
FOR OVER 2000 YEARS.

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JAMES: 
WHEN ALFIRK BECOMES THE NORTH STAR,

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IT WILL HAVE TO SHARE THAT TITLE WITH 
IOTA CEPHEII.

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FOR ALMOST 2000 YEARS, THEY WILL SEEM TO PERFORM 
A NIGHTLY INTERSTELLAR WALTZ AROUND OUR NORTH

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CELESTIAL POLE.

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DEAN: 
IOTA CEPHEII IS A SINGLE STAR, APPROXIMATELY

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206 LIGHT YEARS 
AWAY FROM US.

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IT S OVER TWICE THE MASS, OVER 57 TIMES 
AS BRIGHT AND OVER

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11 TIMES AS WIDE AS 
OUR SUN.

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JAMES: 
THE FIFTH STAR IN CEPHEUS IS ZETA CEPHEII;

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AN ORANGE SUPERGIANT STAR OVER 830 LIGHT YEARS 
AWAY AND OVER

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8 TIMES THE MASS 
OF OUR SUN.

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THE MASS VALUE IS IMPORTANT, 
BECAUSE IT"S VERY LIKELY

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FROM WHAT WE KNOW ABOUT THE PROCESSES THAT 
HAPPEN

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WITHIN A STAR, 
THAT ZETA CEPHEII HAS

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A ENOUGH MASS TO ULTIMATELY GO SUPERNOVA.

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DEAN: 
THE LAST STAR WE LL TALK ABOUT IS

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ONE OF MY FAVORITES.

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IT S DELTA CEPHEII AND IT S JUST UP AND 
TO THE RIGHT OF ZETA CEPHEII.

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THIS STAR IS SPECIAL BECAUSE IT S THE PROTOTYPE 
FOR A CLASS OF STAR ASTRONOMERS CALL CEPHEID

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VARIABLES, AND IT S BECAUSE OF THIS STAR 
THAT WE KNOW THE DISTANCES TO NEARBY GALAXIES

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AND REALIZED THAT THE UNIVERSE 
IS EXPANDING.

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JAMES: 
IN 1784

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A YOUNG ENGLISH ASTRONOMER NAMED JOHN GOODRICKE 
BEGAN OBSERVING DELTA CEPHEII AND NOTICED

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OVER TIME THAT IT VARIED IN BRIGHTNESS AT 
REGULAR INTERVALS.

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THIS DISCOVERY LAID THE GROUND WORK FOR MEASURING 
DISTANCES

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IN THE UNIVERSE.

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DEAN: 
IN 1908, ASTRONOMER HENRIETTA LEVITT WAS STUDYING

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THOUSANDS OF VARIABLE STARS IN THE MAGELLANIC 
CLOUDS AND SHE NOTICED THAT NUMEROUS STARS

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WERE FOUND TO HAVE THIS SAME RELATIONSHIP 
BETWEEN THEIR LUMINOSITY AND THEIR PULSATION

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PERIOD.

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JAMES: 
ONCE THE PULSATION PERIOD FOR A PARTICULAR

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CEPHEID VARIABLE WAS DETERMINED, ASTRONOMERS 
COULD GET AN ACCURATE MEASUREMENT OF THE STAR S

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DISTANCE, 
BY COMPARING THE STAR S LUMINOSITY (WHICH

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WE ALREADY KNEW) TO IT S OBSERVED BRIGHTNESS.

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DEAN: 
THIS RELATIONSHIP WAS SO STRONG THAT IT ALLOWED

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SUBSEQUENT ASTRONOMERS TO ESTABLISH THE SIZE 
AND SHAPE OF OUR GALAXY AND TO DETERMINE THE

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DISTANCES TO OTHER GALAXIES.

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BOTH: KEEP LOOKING UP!

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DEAN: 
SO, THERE YOU HAVE IT.

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A HOUSE-SHAPED CONSTELLATION THAT SURPRISINGLY 
GAVE US INSIGHT INTO THE TRUE DISTANCES IN

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OUR UNIVERSE.

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JAMES: 
ISN T ASTRONOMY WONDERFUL?

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AND IT S ALL WAITING FOR YOU WHEN YOU

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BOTH: KEEP LOOKING UP!