STAR GAZERS
SG 1515 - 5 MINUTE
APRIL 13-19, 2015
"ALBEDO"
JAMES: GREETINGS FELLOW STARGAZERS! 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.
ALTHOUGH THE MOON, VENUS AND JUPITER ARE OFTEN THE BRIGHTEST OBJECTS IN OUR
NIGHT SKY, DID YOU KNOW THAT THE MOON ISN'T AS BRIGHT AS YOU THINK.
JAMES: PLUS, TWO OF THOSE BRIGHT OBJECTS ARE ON THEIR WAY TO A SUPER CLOSE
ENCOUNTER IN A FEW MONTHS. WHAT ARE WE TALKING ABOUT? LET'S SHOW YOU!
(STOP)
JAMES: ALRIGHTY! WE HAVE OUR SKIES SET UP FOR JUST AFTER SUNSET IN THE EARLY
PART OF NEXT WEEK, FACING WEST. ON TUESDAY, APRIL 21ST, YOU'LL SEE A SLENDER
WAXING CRESCENT MOON AMONG THE STARS OF TAURUS THE BULL. AS THE SKY GETS
DARKER, YOU MAY SEE A PHENOMENON THAT IS OFTEN REFERRED TO AS THE "OLD MOON IN
THE NEW MOON'S ARMS". IF YOU LOOK AT THE DARK PORTION OF THE MOON, YOU'LL BARELY
MAKE OUT THE PATTERN OF THE MAN IN THE MOON, HIDING IN THE DARKNESS. AND YOU CAN
SPOT THIS EVERY MONTH WITHIN A FEW DAYS AFTER NEW MOON.
DEAN: THAT'S RIGHT, JAMES. WHAT YOU'RE SEEING IS CALLED "EARTHSHINE". THIS
HAPPENS WHEN SUNLIGHT REFLECTED FROM THE EARTH ILLUMINATES THE NIGHTTIME SIDE
OF THE MOON. TYPICALLY, THIS RESULTS IN THE MOON'S NIGHTTIME SIDE BEING BATHED IN A
SOFT, FAINT LIGHT.
JAMES: WE ASTRONOMERS USE THE TERM ALBEDO TO DESCRIBE THE REFLECTIVITY OF A
PLANET OR MOON. WHEN THE MOON IS FULL, IT SEEMS LIKE THE BRIGHTEST THING AROUND.
IN ACTUALITY, THE MOON HAS ALMOST THE SAME REFLECTIVITY AS CHARCOAL. YOU MIGHT
BE SURPRISED TO KNOW THAT THE MOON'S ALBEDO IS A PITIFUL 0.136. THIS MEANS THAT
BARELY 14% OF THE SUNLIGHT STRIKING THE MOON'S SURFACE IS REFLECTED BACK INTO
SPACE.
(STOP)
DEAN: EARTH'S ALBEDO IS A LITTLE LARGER. SINCE WE HAVE FLUFFY WHITE CLOUDS AND
CONTINENTS THAT ARE OCCASIONALLY COVERED WITH SNOW, EARTH'S ALBEDO IS AT 39%
OR 0.39. VENUS HOWEVER WINS ON THE REFLECTIVITY SCALE. SINCE VENUS IS
PERPETUALLY COVERED IN A THICK LAYER OF CLOUDS, IT HAS AN ALBEDO OF ALMOST 70%
AT 0.69.
JAMES: IF THE MOON'S ALBEDO WERE THAT HIGH, WE PROBABLY WOULDN'T NEED STREET
LIGHTS.
DEAN: AND LOOKING AT THE STARS WOULD BE NEARLY IMPOSSIBLE DURING THE GIBBOUS
AND FULL PHASES OF THE MOON.
JAMES: HOORAY FOR CHARCOAL COLORED MOONS!
DEAN: NOW IF THAT WEREN'T EXCITING ENOUGH, DID YOU KNOW THAT THE BOUNDARY
BETWEEN THE DAYTIME AND NIGHTTIME SIDE OF THE MOON ACTUALLY HAS A NAME? WE
ASTRONOMERS CALL IT… "THE TERMINATOR".
JAMES (IN SCHWARZENEGGER VOICE): HASTA LA VISTA, BABY.
DEAN: NO, NOT THAT TERMINATOR.
JAMES: OH.
DEAN: BUT WE'LL BE BACK.
(STOP)
DEAN: ON APRIL 21ST, TAKE A LOOK TO THE RIGHT OF THE MOON AND YOU'LL SEE OUR
SISTER PLANET, VENUS; NAMED AFTER THE ROMAN GODDESS OF BEAUTY AND LOVE. WHEN
VENUS IS VISIBLE JUST AFTER SUNSET, WE EARLY EVENING STAR GAZERS LIKE TO CALL
VENUS, THE EVENING STAR.
JAMES: AND WHEN VENUS IS VISIBLE JUST BEFORE SUNRISE, WE EARLY MORNING STAR
GAZERS REFER TO VENUS AS THE MORNING STAR. AS THE WEEKS PASS, YOU'LL NOTICE
THAT VENUS IS SLOWLY MAKING A TREK ACROSS THE SKY TO A CLOSE ENCOUNTER ON JUNE
30TH WITH THE SECOND BRIGHTEST PLANET IN THE SOLAR SYSTEM, GIANT JUPITER.
DEAN: EVEN THOUGH JUPITER IS MANY TIMES FARTHER FROM US THAN VENUS, JUPITER IS
BRIGHT BECAUSE NOT ONLY IS IT COVERED WITH CLOUDS, IT'S HUGE!
JAMES: JUPITER IS ALMOST 88,000 MILES IN DIAMETER AND HAS AN ALBEDO OF OVER 50% AT
0.52. SO ON MOST NIGHTS, WHEN JUPITER IS ON THE SAME SIDE OF THE SUN AS WE ARE,
JUPITER RIVALS VENUS IN BRIGHTNESS. THE TRICK FOR TELLING JUPITER FROM VENUS WITH
THE NAKED EYE IS THAT VENUS IS ALWAYS NEAR THE SUN BECAUSE IT ORBITS CLOSER TO
THE SUN THAN WE DO.
DEAN: JUPITER ON THE OTHER HAND HAS A LARGER ORBIT THAN WE DO, SO IT CAN APPEAR
UP TO 180 DEGREES AWAY FROM THE SUN IN THE SKY. HOWEVER, NO MATTER WHERE
JUPITER APPEARS IN THE SKY, IT'S ALWAYS DIMMER THAN VENUS.
(STOP)
JAMES: AS OUR POSITION IN THE SOLAR SYSTEM CHANGES THE PLANETS (WHICH ARE ALSO
ORBITING THE SUN), WILL APPEAR TO CHANGE POSITION AGAINST THE BACKGROUND STARS.
DEAN: SO AS OUR PERSPECTIVE CHANGES, JUPITER WILL APPEAR TO RISE EARLIER AND
EARLIER AND VENUS WILL BE SETTING LATER AND LATER.
JAMES: AND... ON THE NIGHT OF JUNE 30TH THEY WILL APPEAR RIGHT NEXT TO EACH OTHER
IN WHAT WE CALL A CONJUNCTION OR.. A SUPER SCOOTCHIE! SO MARK YOUR CALENDARS!
DEAN: SO GET OUTSIDE AND SOAK UP SOME REFLECTED SUNLIGHT FROM THE THREE
BRIGHTEST OBJECTS IN OUR NIGHT SKY.
JAMES: THE MOON , VENUS, AND JUPITER
BOTH: KEEP LOOKING UP!