GALAXIES GALAXIES GALAXIES ARE HUGE COLLETCTIONS OF STARS

GALAXIES

GALAXIES • GALAXIES ARE HUGE COLLETCTIONS OF STARS • GRAVITY HOLDS STARS AND GALAXIES TOGETHER • WHEN ASTRONOMERS EXAMINE HOW GALAXIES ROTATE AND GRAVITATIONALLY INTERACT, THEY FIND THAT MOST OF THE MATTER IN GALAXIES IS INVISIBLE • MATTER THAT EMITS NO LIGHT AT ANY WAVELENGTH IS DARK MATTER • MAJOR TYPES OF GALAXIES ARE: • SPIRAL • ELLIPTICAL • IRREGULAR

SPIRAL GALAXIES • SPIRAL ARMS OF STARS, GAS, AND DUST EXTENDED FROM CENTRAL DISK • SPIRAL GALAXIES HAVE A CENTRAL BULGE • A SPHERICAL HALO SURROUNDS THE DISK

ELLIPTICAL GALAXIES • ELLIPTICAL GALAXIES HAVE A SPHERICAL OR ELLIPTICAL SHAPE AND NO INTERNAL STRUCTURE • THEY CONTAIN MORE OLDER STARS THAN SPIRAL GALAXIES, AND MAY HAVE FORMED AS SPIRAL GALAXIES MERGED

IRREGULAR GALAXIES • IRREGULAR GALAXIES ARE ODDLY SHAPED AND CONTAIN MANY YOUNG STARS

THE MILKY WAY • THE ROMANS CALLED IT THE “VIA GALACTICA” (THE ROAD OF MILK) • THE SOLAR SYSTEM IS IN THE MILKY WAY, A SPIRAL GALAXY THAT CONTAINS GAS, DUST, AND ALMOST 200 BILLION STARS • THE MILKY WAY IS A MEMBER OF THE LOCAL GROUP, A CLUSTER OF ABOUT 30 GALAXIES

ELECTROMAGNETIC SPECTRUM • WAVELENGTH IS FROM ONE POINT ON THE NEXT WAVE. • LONGER WAVELENGTH – LOWER FREQUENCY – LOWER ENERGY • SHORTER WAVELENGTH – HIGHER FREQUENCY – HIGHER ENERGY

DOPPLER SHIFT • THE SHIFT TO A DIFFERENT WAVELENGTH IS CALLED THE DOPPLER SHIFT • IF MOVING TOWARD THE OBSERVER WAVELENGTH SHORTENS, IF MOVING AWAY, THE WAVELENGTHENS

DOPPLER SHIFT • WHEN LIGHT TRAVELS AWAY FROM YOU, ITS WAVELENGTH STRETCHES OUT, SHIFTING TO THE RED END OF THE ELECTROMAGNETIC SPECTRUM • THIS CALLED “RED SHIFT”

EXPANDING UNIVERSE • GALAXIES ARE “RED SHIFTED” • SCIENTISTS OBSERVE HOW SPACE STRETCHES BY MEASURING THE SPEED AT WHICH GALAXIES MOVE AWAY FROM THE EARTH • SCIENTISTS AGREE THAT THE UNIVERSE IS 13 -14 BILLION YEARS OLD • ACCORDING TO THE BIG BANG THEORY, THE UNIVERSE BEGAN FROM ONE POINT BILLIONS OF YEARS AGO AND HAS BEEN EXPANDING EVER SINCE