WEBVTT

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ANDROMEDAS FATHER!

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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 NIGHT SKY.

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

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JAMES:
AND MORE EXCITINGLY, ONE OF IT'S 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 WERE TALKING ABOUT?

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LETS 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 TO

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CAPH AND KEEP ON GOING, YOU'LL RUN
SMACK DAB INTO A CONSTELLATION THAT LOOKS

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LIKE AN
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 ALDERAMIN

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AND ITS 49 LIGHT YEARS AWAY FROM US.

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IT'S BAYER DESIGNATION IS ALPHA CEPHEII, SO
NAMED BY GERMAN ASTRONOMER JOHANN BAYER, WHO

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NAMED THE STARS WITH A GREEK LETTER (BASED
ON THEIR BRIGHTNESS) AND THE LATINIZED NAME

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OF THE CONSTELLATION.

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BEING THE BRIGHTEST STAR IN CEPHEUS, IT WAS
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, EARTHS ROTATIONAL
AXIS PASSES THROUGH SEVERAL CONSTELLATIONS,

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TRACING A GIANT CIRCLE IN 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:
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 A BINARY

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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 MORE.

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IN 5200 AD IT WILL HAVE
TO RELINQUISH THE TITLE TO BOTH ALFIRK AND

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THE NEXT STAR IN CEPHEUS, IOTA CEPHEII.

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JAMES:
IN 6000 AD, THE EARTHS AXIS WILL POINT SMACK

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DAB IN THE MIDDLE - BETWEEN ALFIRK AND IOTA
CEPHEII; AND FOR ALMOST 2000 YEARS,

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THEY WILL SEEM TO PERFORM A NIGHTLY WALTZ
AROUND OUR NORTH 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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ITS OVER TWICE THE MASS AND OVER 57 TIMES
AS BRIGHT 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 ITS VERY
LIKELY, FROM WHAT WE KNOW ABOUT THE PROCESSES

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THAT HAPPEN WITHIN A STAR, THAT ZETA CEPHEII
HAS A ENOUGH MASS TO ULTIMATELY

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GO SUPERNOVA, PRODUCING A VERY DENSE WHITE
DWARF

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AS A RESULT.

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DEAN:
THE LAST STAR WE'LL TALK ABOUT IS ONE OF

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MY FAVORITES.

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

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THIS STAR IS SPECIAL BECAUSE ITS THE PROTOTYPE
FOR A CLASS OF STARS THAT ASTRONOMERS CALL

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CEPHEID VARIABLES,
AND ITS BECAUSE OF THIS STAR THAT WE KNOW

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THE DISTANCES TO NEARBY GALAXIES.

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JAMES:
IN 1784 A YOUNG ENGLISH ASTRONOMER NAMED JOHN

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GOODRICKE BEGAN OBSERVING DELTA CEPHEII AND
NOTICED THAT IT VARIED IN BRIGHTNESS AT REGULAR

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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 MANY STARS WERE

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FOUND TO HAVE THIS SAME RELATIONSHIP.

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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 STARS

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DISTANCE, BY COMPARING THE STARS KNOWN LUMINOSITY
TO ITS OBSERVED BRIGHTNESS.

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DEAN:
THIS RELATIONSHIP WAS SO STRONG THAT IT ALLOWED

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ASTRONOMERS TO ESTABLISH THE SIZE AND SHAPE
OF OUR GALAXY.

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JAMES:
ISNT ASTRONOMY WONDERFUL?

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AND ITS ALL WAITING FOR YOU WHEN YOU

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BOTH: KEEP LOOKING UP!