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OBSERVING THE UNIVERSE
CHAPTER 4
STARS
• STARS PRODUCE AND
RADIATE ENERGY
(“RADIANT ENERGY”)
• THE ENERGY THAT THEY EMIT
TRAVELS IN WAVES CALLED
ELECTROMAGNETIC WAVES
ELECTROMAGNETIC WAVES
VS.
MECHANICAL WAVES
THE MAJOR DIFFERENCE BETWEEN MECHANICAL AND ELECTROMAGNETIC WAVES IS
THAT MECHANICAL WAVES CAN ONLY MOVE THROUGH MATTER (WATER, LIQUID, GAS)
AND ELECTROMAGNETIC WAVES CAN MOVE THROUGH MATTER OR THROUGH A
VACUUM (SUCH AS SPACE)
ELECTROMAGNETIC SPECTRUM
THE ENTIRE RANGE OF RADIANT ENERGY CARRIED BY ELECTROMAGNETIC
WAVES IS THE ELECTROMAGNETIC SPECTRUM
A wave is classified by its wavelength
LONG VS. SHORT WAVES
• LONG WAVE LENGTHS = LOW FREQUENCIES AND LOW ENERGY
• SHORT WAVE LENGTHS = HIGH FREQUENCIES AND HIGH ENERGY
RADIANT ENERGY AND STARS
• MOST STARS EMIT ENERGY IN ALL WAVELENGTHS
• HOT STARS: SHORTER WAVES WITH HIGHER ENERGY
• COOL STARS: LONGER WAVES WITH LOW ENERGY
OUR SUN HAS A MEDIUM TEMPERATURE RANGE. THEREFORE, IT EMITS MOST
OF ITS ENERGY IN THE FORM OF VISIBLE LIGHT.
ELECTROMAGNETIC SPECTRUM FOLDABLE
1. LABEL THE OUTSIDE OF YOUR FLAPS WITH
THE APPROPRIATE TYPE OF WAVE
2. PUT THE FOLLOWING CHARACTERISTICS UNDER THE APPROPRIATE WAVE:
• SHORTEST WAVELENGTHS
• LONGEST WAVELENGTHS
• USED IN BROADCASTING
• HIGHEST FREQUENCIES
• LOWEST FREQUENCIES
• WE CAN SEE IT!
• TOO MUCH EXPOSURE CAN CAUSE CANCER
• ENERGY IS GREAT ENOUGH TO DAMAGE OR KILL LIVING CELLS
• INSECTS CAN SEE THIS
• WHITE LIGHT CAN BE SEPARATED INTO RED, ORANGE, YELLOW, GREEN, BLUE, INDIGO AND VIOLET
• USED IN RADAR GUNS
• USEFUL IN MEDICINE
• WE FEEL THEM AS HEAT
THE SPEED OF LIGHT
ALL ELECTROMAGNETIC WAVES TRAVEL THROUGH SPACE AT A
CONSTANT SPEED (THE SPEED OF LIGHT):
300,000 KM/S
• REFLECTED LIGHT FROM THE MOON TAKES ABOUT 1 SECOND TO REACH EARTH
• LIGHT FROM THE SUN TAKES ABOUT 8.3 MINUTES TO REACH EARTH
• LIGHT FROM THE SUN TAKES ABOUT 40 MINUTES TO REACH JUPITER
• SOME STARS ARE SO FAR AWAY THAT IT CAN TAKE MILLIONS OR BILLIONS OF YEARS
FOR THEIR RADIANT ENERGY TO REACH EARTH (ASTRONOMERS CAN STUDY THOSE
STARS TO KNOW WHAT THE UNIVERSE WAS LIKE A VERY LONG TIME AGO)
TELESCOPES
TELESCOPES ENABLE ASTRONOMERS
TO OBSERVE MANY MORE STARS THAN THEY COULD WITH
THEIR EYES BECAUSE THEY
GATHER AND FOCUS LIGHT FROM OBJECTS IN SPACE
EARTH BASED TELESCOPES
2 TYPES:
1.OPTICAL TELESCOPES: DETECTS AND
COLLECTS VISIBLE LIGHT
2.RADIO TELESCOPES: DETECTS AND COLLECTS
RADIO WAVES (AND SOME MICROWAVES)
OPTICAL TELESCOPES
2 TYPES:
1. REFRACTING TELESCOPE: USES A CONVEX
LENS TO CONCENTRATE LIGHT FROM A DISTANT
OBJECT
2. REFLECTING TELESCOPE: USES A CURVED
MIRROR TO CONCENTRATE LIGHT FROM A DISTANT
OBJECT
WHY ARE MOST OPTICAL TELESCOPES BUILT ON MOUNTAINS?
RADIO TELESCOPES
• A TELESCOPE THAT COLLECTS RADIO WAVES AND SOME
MICROWAVES USING AN ANTENNA THAT LOOKS LIKE A TV
SATELLITE DISH.
• RADIO ANTENNA MUST
BE LARGE.
WHY?
WHY ARE MOST RADIO TELESCOPES LOCATED IN DRY DESERTS?
WHY DO WE ONLY HAVE TWO TYPES OF
EARTH-BASED TELESCOPES?
LIMITATIONS OF EARTH-BASED
TELESCOPES
• EARTH’S ATMOSPHERE NOT ONLY DISTORTS IMAGES, BUT ALSO ABSORBS SOME
TYPES OF ELECTROMAGNETIC RADIATION.
• ONLY VISIBLE LIGHT, RADIO WAVES, AND SOME MICROWAVES REACH EARTH’S
SURFACE, THEREFORE, EARTH-BASED TELESCOPES ARE LIMITED TO COLLECTING
THESE TYPES OF WAVES.
• HOWEVER, TELESCOPES IN SPACE CAN COLLECT ENERGY AT ALL
WAVELENGTHS!
OPTICAL SPACE TELESCOPES
• TELESCOPES THAT COLLECT VISIBLE
LIGHT
• CREATES BETTER IMAGES BECAUSE NO ATMOSPHERE
• 1ST SPACE OPTICAL TELESCOPE: HUBBLE SPACE TELESCOPE (1990)
- REFLECTING TELESCOPE THAT ORBITS EARTH
SPACE TELESCOPES THAT USE OTHER
WAVELENGTHS
• THERE ARE OTHER SPACE TELESCOPES (OPERATED BY OTHER COUNTRIES)
GAMMA RAYS, UV RAYS, X-RAY, AND INFRARED WAVELENGTHS.
• IMAGES OF OBJECTS
THAT COLLECT
IN SPACE CAN BE CREATED BY A COMBINATION OF DATA FROM THESE
DIFFERENT TYPES OF SPACE TELESCOPES.
This image of the star Cassiopeia was made
with a combination of optical, X-ray, and
infrared data.
SPITZER SPACE TELESCOPE
• COLLECTS INFRARED WAVES
• ORBITS THE SUN
• USED TO VIEW YOUNG STARS
AND PLANETS HIDDEN BY GAS
AND DUST
JAMES WEBB SPACE TELESCOPE
• COLLECT INFRARED RADIATION
• ORBITS THE SUN
• SCHEDULED
FOR LAUNCH IN
2018
• WILL BE USED TO DETECT GALAXIES
THAT FORMED VERY EARLY IN THE HISTORY
OF THE UNIVERSE