CEPHEUS!
JAMES:
WELCOME TO STAR GAZERS.
I'M JAMES ALBURY, DIRECTOR OF THE KIKA SILVA
PLA PLANETARIUM IN GAINESVILLE FLORIDA.
DEAN:
AND I'M DEAN REGAS, ASTRONOMER FROM THE CINCINNATI
OBSERVATORY.
WE RE HERE TO HELP YOU FIND YOUR WAY AROUND
THE SKY.
THIS WEEK, WE RE GOING TO TALK ABOUT A CONSTELLATION
THAT S PART OF AN ANCIENT CELESTIAL STORY.
JAMES:
AND MORE EXCITINGLY, ONE OF ITS STARS HELPED
ASTRONOMERS DETERMINE THE SIZE AND SHAPE OF
OUR OWN GALAXY AND THE DISTANCES TO NEARBY
GALAXIES.
WONDERING WHAT WE RE TALKING ABOUT?
LET S SHOW YOU!
JAMES:
OK, WE HAVE OUR SKIES SET FOR AN HOUR AFTER
SUNSET, ANY NIGHT THIS WEEK, FACING NORTH.
OFF TO THE NORTHEAST YOU LL SEE THE FAMILIAR
W-SHAPED PATTERN OF CASSIOPEIA THE QUEEN.
THE STARS THAT MARK THIS CONSTELLATION, STARTING
FROM THE TOP DOWN ARE CAPH, SHEDAR, TSIH,
RUCHBAH
AND SEGIN.
DEAN:
IF YOU DRAW A STRAIGHT LINE FROM SHEDAR
TO CAPH AND
KEEP ON GOING,
YOU LL RUN SMACK DAB INTO A CONSTELLATION
THAT LOOKS LIKE AN
UPSIDE-DOWN HOUSE.
THIS IS CEPHEUS THE KING.
CEPHEUS WAS THE HUSBAND OF CASSIOPEIA AND
FATHER OF ANDROMEDA.
JAMES:
THE BRIGHTEST STAR IN CEPHEUS IS TOWARD THE
UPPER LEFT AT THIS TIME OF NIGHT IN OCTOBER.
THAT STAR S NAME IS ALDERAMIN AND IT S
49 LIGHT YEARS
AWAY FROM US.
SINCE IT IS THE BRIGHTEST STAR
IN CEPHEUS,
IT IS NAMED ALPHA CEPHEII.
DEAN:
ALDERAMIN LIES VERY CLOSE TO A REGION OF THE
NORTHERN SKY CALLED THE
PRECESSION CIRCLE.
OVER A PERIOD OF
26,000 YEARS,
EARTH S ROTATIONAL AXIS PASSES THROUGH SEVERAL
CONSTELLATIONS, TRACING A GIANT CIRCLE IN
THE SKY.
RIGHT NOW, OUR ROTATIONAL AXIS IS POINTING
TOWARD POLARIS; OUR CURRENT NORTH STAR.
HOWEVER, IN 7500 AD, ALDERAMIN WILL BE OUR
NORTH STAR.
JAMES:
I'LL BE SURE TO MARK THAT ON MY CALENDAR.
JAMES:
TRAVELING COUNTER CLOCKWISE FROM ALDERAMIN,
WE HAVE ALFIRK, ALSO KNOWN AS BETA CEPHEII.
ALFIRK IS A MULTIPLE STAR SYSTEM APPROXIMATELY
690 LIGHT YEARS FROM EARTH.
ALFIRK WILL BE OUR NORTH STAR BETWEEN 5200
AD AND 7500 AD.
DEAN:
THE NEXT STAR IN CEPHEUS IS ERRAI;
ALSO KNOWN AS GAMMA CEPHEII.
ERRAI MARKS THE POINT ON THE ROOF OF THIS
HOUSE-SHAPED CONSTELLATION AND IS
A BINARY STAR SYSTEM APPROXIMATELY 45 LIGHT
YEARS AWAY.
ERRAI WILL BECOME OUR NORTH STAR IN LESS THAN
A THOUSAND YEARS,
AND IT WILL RETAIN THE TITLE OF NORTH STAR
FOR OVER 2000 YEARS.
JAMES:
WHEN ALFIRK BECOMES THE NORTH STAR,
IT WILL HAVE TO SHARE THAT TITLE WITH
IOTA CEPHEII.
FOR ALMOST 2000 YEARS, THEY WILL SEEM TO PERFORM
A NIGHTLY INTERSTELLAR WALTZ AROUND OUR NORTH
CELESTIAL POLE.
DEAN:
IOTA CEPHEII IS A SINGLE STAR, APPROXIMATELY
206 LIGHT YEARS
AWAY FROM US.
IT S OVER TWICE THE MASS, OVER 57 TIMES
AS BRIGHT AND OVER
11 TIMES AS WIDE AS
OUR SUN.
JAMES:
THE FIFTH STAR IN CEPHEUS IS ZETA CEPHEII;
AN ORANGE SUPERGIANT STAR OVER 830 LIGHT YEARS
AWAY AND OVER
8 TIMES THE MASS
OF OUR SUN.
THE MASS VALUE IS IMPORTANT,
BECAUSE IT"S VERY LIKELY
FROM WHAT WE KNOW ABOUT THE PROCESSES THAT
HAPPEN
WITHIN A STAR,
THAT ZETA CEPHEII HAS
A ENOUGH MASS TO ULTIMATELY GO SUPERNOVA.
DEAN:
THE LAST STAR WE LL TALK ABOUT IS
ONE OF MY FAVORITES.
IT S DELTA CEPHEII AND IT S JUST UP AND
TO THE RIGHT OF ZETA CEPHEII.
THIS STAR IS SPECIAL BECAUSE IT S THE PROTOTYPE
FOR A CLASS OF STAR ASTRONOMERS CALL CEPHEID
VARIABLES, AND IT S BECAUSE OF THIS STAR
THAT WE KNOW THE DISTANCES TO NEARBY GALAXIES
AND REALIZED THAT THE UNIVERSE
IS EXPANDING.
JAMES:
IN 1784
A YOUNG ENGLISH ASTRONOMER NAMED JOHN GOODRICKE
BEGAN OBSERVING DELTA CEPHEII AND NOTICED
OVER TIME THAT IT VARIED IN BRIGHTNESS AT
REGULAR INTERVALS.
THIS DISCOVERY LAID THE GROUND WORK FOR MEASURING
DISTANCES
IN THE UNIVERSE.
DEAN:
IN 1908, ASTRONOMER HENRIETTA LEVITT WAS STUDYING
THOUSANDS OF VARIABLE STARS IN THE MAGELLANIC
CLOUDS AND SHE NOTICED THAT NUMEROUS STARS
WERE FOUND TO HAVE THIS SAME RELATIONSHIP
BETWEEN THEIR LUMINOSITY AND THEIR PULSATION
PERIOD.
JAMES:
ONCE THE PULSATION PERIOD FOR A PARTICULAR
CEPHEID VARIABLE WAS DETERMINED, ASTRONOMERS
COULD GET AN ACCURATE MEASUREMENT OF THE STAR S
DISTANCE,
BY COMPARING THE STAR S LUMINOSITY (WHICH
WE ALREADY KNEW) TO IT S OBSERVED BRIGHTNESS.
DEAN:
THIS RELATIONSHIP WAS SO STRONG THAT IT ALLOWED
SUBSEQUENT ASTRONOMERS TO ESTABLISH THE SIZE
AND SHAPE OF OUR GALAXY AND TO DETERMINE THE
DISTANCES TO OTHER GALAXIES.
BOTH: KEEP LOOKING UP!
DEAN:
SO, THERE YOU HAVE IT.
A HOUSE-SHAPED CONSTELLATION THAT SURPRISINGLY
GAVE US INSIGHT INTO THE TRUE DISTANCES IN
OUR UNIVERSE.
JAMES:
ISN T ASTRONOMY WONDERFUL?
AND IT S ALL WAITING FOR YOU WHEN YOU
BOTH: KEEP LOOKING UP!