1. NSCI 314 LIFE IN THE COSMOS 2 – ENERGY THE NATURE OF LIGHT BASIC ASTRONOMY STARS AND THEIR SPECTRA Dr. Karen Kolehmainen Department of Physics CSUSB COURSE WEBPAGE: http://physics.csusb.edu/~karen

2. TEMPERATURE MOLECULES ARE ALWAYS IN MOTION. THE DIRECTIONS OF MOTION ARE RANDOM. DIFFERENT MOLECULES MOVE IN DIFFERENT DIRECTIONS. THE HIGHER THE TEMPERATURE OF AN OBJECT, THE FASTER THE MOLECULES INSIDE IT ARE MOVING, ON THE AVERAGE. AT A GIVEN TEMPERATURE, NOT ALL MOLECULES MOVE AT THE SAME SPEED. SOME MOVE FASTER THAN AVERAGE, AND SOME MOVE SLOWER THAN AVERAGE. IMAGINE A COLLECTION OF MOLECULES, SOME LIGHTER AND SOME HEAVIER (EXAMPLE: AIR), ALL AT THE SAME TEMPERATURE. THE LIGHTER MOLECULES ARE FASTER AND THE HEAVIER MOLECULES ARE SLOWER, ON THE AVERAGE.

3. DENSITY AND PRESSURE DENSITY = MASS / VOLUME –VOLUME IS THE AMOUNT OF ROOM (IN 3-D) THAT SOMETHING TAKE UP PRESSURE = FORCE / AREA –THE ATMOSPHERIC PRESSURE ON THE SURFACE OF THE EARTH IS A RESULT OF THE WEIGHT OF THE AIR ABOVE US PRESSING DOWN ON US. –IF YOU MOVE TO A HIGHER ELEVATION, THERE IS LESS AIR ABOVE YOU, SO THE PRESSURE IS LOWER. THIS ALLOWS THE AIR MOLECULES TO SPREAD FARTHER APART, SO THE DENSITY IS ALSO LOWER. ATMOSPHERIC PRESSURE AND DENSITY VARY FROM PLANET TO PLANET.

4. THE DUAL NATURE OF LIGHT: PARTICLES AND WAVES SOMETIMES LIGHT BEHAVES LIKE A WAVE (AN OSCILLATING ELECTROMAGNETIC FIELD). SOMETIMES LIGHT BEHAVES LIKE A STREAM OF PARTICLES. WHICH IS IT? NEITHER IS REALLY CORRECT, BUT BOTH ARE USEFUL WAYS TO THINK ABOUT IT.

5. IF THIS SKETCH REPRESENTS A WATER WAVE, THE HEIGHT OF THE WATER CHANGES AS YOU MOVE TO THE RIGHT OR LEFT. IF IT'S A SOUND WAVE, THE DENSITY AND PRESSURE OF AIR (OR SOME OTHER MATERIAL) CHANGES AS YOU MOVE TO THE LEFT OR RIGHT. IF IT'S A LIGHT WAVE, THE STRENGTH OF AN ELECTROMAGNETIC FIELD CHANGES AS YOU MOVE TO THE RIGHT OR LEFT. THE WAVE TRAVELS EITHER TO THE RIGHT OR LEFT. ALL WAVES CARRY ENERGY AS THEY MOVE. SPEED OF LIGHT: c = 300,000 km/s = 1 light year / year (SAME SPEED FOR ALL LIGHT WAVES IN A VACUUM)‏ THE WAVE NATURE OF LIGHT

6. WAVELENGTH = DISTANCE BETWEEN TWO ADJACENT PEAKS FREQUENCY = NUMBER OF WAVES OR PEAKS PASSING BY A GIVEN LOCATION PER SECOND 1 Hertz = 1 wave per second passing by 1 kHz = 1,000 Hz 1 MHz = 1,000 kHz = 1,000,000 Hz WAVELENGTH x FREQUENCY = SPEED OF WAVE THE WAVE NATURE OF LIGHT

7. WAVELENGTH x FREQUENCY = SPEED OF WAVE SINCE THE SPEED IS THE SAME FOR ALL LIGHT WAVES (c), LARGER FREQUENCY MEANS SMALLER WAVELENGTH, AND VICE VERSA. FOR LIGHT WAVES, FREQUENCY AND WAVELENGTH ARE RELATED TO COLOR. -THE SMALLER THE WAVELENGTH, THE LARGER (OR HIGHER) THE FREQUENCY, AND THE BLUER THE COLOR. -THE LARGER THE WAVELENGTH, THE SMALLER (OR LOWER) THE FREQUENCY, AND THE REDDER THE COLOR. THE WAVE NATURE OF LIGHT

8. AMPLITUDE = HEIGHT OF THE WAVE (TECHNICALLY, IT'S DEFINED AS HALF OF THE TOTAL HEIGHT)‏ FOR LIGHT WAVES, THE AMPLITUDE IS RELATED TO THE BRIGHTNESS: - THE LARGER THE AMPLITUDE, THE BRIGHTER THE LIGHT. - THE SMALLER THE AMPLITUDE, THE FAINTER THE LIGHT. THE WAVE NATURE OF LIGHT

9. THE PARTICLE NATURE OF LIGHT A PARTICLE OF LIGHT IS CALLED A PHOTON. A PHOTON CARRIES ENERGY. THE AMOUNT OF ENERGY THAT EACH PHOTON HAS IS RELATED TO THE COLOR OF THE LIGHT (AND THEREFORE ALSO TO WAVELENGTH AND FREQUENCY OF THE CORRRESPONDING WAVE). THE LARGER THE ENERGY PER PHOTON – THE SHORTER THE WAVELENGTH – THE HIGHER THE FREQUENCY – THE BLUER THE COLOR THE SMALLER THE ENERGY PER PHOTON – THE LONGER THE WAVELENGTH – THE LOWER THE FREQUENCY – THE REDDER THE COLOR

10. LONG WAVELENGTH --> LOW FREQUENCY --> LOW ENERGY PER PHOTON SHORT WAVELENGTH --> HIGH FREQUENCY --> HIGH ENERGY PER PHOTON ELECTROMAGNETIC SPECTRUM TYPE GAMMA RAYS X- RAYS ULTRAVIOLET VISIBLE LIGHT INFRARED MICROWAVE TV & FM RADIO AM RADIO WAVELENGTH SIZE OF ATOM VIRUS BACTERIA DUST 1 cm 1 m 100 m FREQUENCY VERY HIGH HIGH BILLION MHz MILLION MHz 1000 MHz 100MHz 1000 kHz PURPLE BLUE GREEN YELLOW ORANGE RED

11. ENERGY ENERGY IS WHAT MAKES THINGS HAPPEN. CONSERVATION OF ENERGY: ENERGY CANNOT BE CREATED OR DESTROYED. ENERGY CAN BE CHANGED FROM ONE FORM TO ANOTHER. ENERGY CAN BE TRANSFERRED FROM ONE OBJECT TO ANOTHER.

12. FORMS OF ENERGY KINETIC ENERGY – ENERGY OF MOTION POTENTIAL (STORED) ENERGY – ELASTIC (EXAMPLE: STRETCHED OR COMPRESSED SPRING) ‏ – GRAVITATIONAL – ELECTRICAL – CHEMICAL – NUCLEAR LIGHT SOUND THERMAL (HEAT) ENERGY – KINETIC ENERGY OF RANDOM MOTION OF MOLECULES MASS (E = m c 2 ) ‏

13. SOME BASIC ASTRONOMY STAR: A VERY LARGE, HOT BALL OF GAS THAT EMITS LARGE AMOUNTS OF LIGHT. THE LIGHT AND HEAT ARE PRODUCED BY NUCLEAR FUSION (SMALL NUCLEI COMBINING TO PRODUCE LARGER NUCLEI) OCCURRING IN THE CENTER OF THE STAR. PLANET : A FAIRLY LARGE OBJECT (BUT MUCH SMALLER THAN A STAR) THAT ORBITS AROUND A STAR. IT CAN BE ROCKY OR GASEOUS. THERE IS NO NUCLEAR FUSION OCCURRING INSIDE. MOON: A SMALLER OBJECT THAT ORBITS AROUND A PLANET.

14. SOME BASIC ASTRONOMY EARTH: THE PLANET UPON WHICH WE LIVE. SUN: THE STAR AROUND WHICH THE EARTH ORBITS. SOLAR SYSTEM: OUR SUN, THE 8 PLANETS AND SMALLER BODIES (DWARF PLANETS, COMETS, ASTEROIDS, ETC.) THAT ORBIT IT, AND THE MOONS THAT ORBIT THE PLANETS. GALAXY: A LARGE CLUSTER OF STARS (1 MILLION TO 1 TRILLION STARS). MANY OF THESE STARS HAVE THEIR OWN SOLAR SYSTEMS. THE MILKY WAY: THE GALAXY IN WHICH OUR SOLAR SYSTEM IS LOCATED. IT CONTAINS ABOUT 400 BILLION STARS, PLUS THE PLANETS AND SMALLER BODIES ORBITING THESE STARS.

15. SOME BASIC ASTRONOMY UNIVERSE: EVERYTHING THAT EXISTS. WITH POWERFUL TELESCOPES, WE CAN SEE ABOUT 100 BILLION OBSERVABLE GALAXIES. THE TOTAL NUMBER OF GALAXIES IN THE UNIVERSE IS LIKELY TO BE MUCH HIGHER, PROBABLY AT LEAST 1 TRILLION. BIG BANG: AN EXPLOSION THAT STARTED THE UNIVERSE APPROXIMATELY 13.7 BILLION YEARS AGO. ALL OF THE MATTER IN THE UNIVERSE WAS EXPELLED OUTWARD FROM THE EXPLOSION. GALAXIES ARE STILL MOVING APART FROM EACH OTHER AS A RESULT. (BY COMPARISON, OUR SOLAR SYSTEM IS ONLY 4.6 BILLION YEARS OLD.) ‏

16. MOTIONS IN THE SOLAR SYSTEM EACH PLANET SPINS OR ROTATES ON ITS OWN AXIS, PRODUCING DAY AND NIGHT. THE EARTH SPINS ONCE EVERY 24 HOURS (1 DAY). EACH PLANET ORBITS OR REVOLVES AROUND THE SUN. THE EARTH COMPLETES ONE ORBIT IN 365 DAYS (1 YEAR). THE FARTHER A PLANET IS FROM THE SUN, THE LONGER IT TAKES TO COMPLETE ONE ORBIT (IN OTHER WORDS,THE LONGER ITS YEAR). MOONS ORBIT AROUND PLANETS. THE EARTH'S MOON TAKES ABOUT A MONTH TO COMPLETE ONE ORBIT AROUND THE EARTH. SEASONS ARE CAUSED BY THE FACT THAT THE EARTH'S ROTATIONAL AXIS (THE LINE IT ROTATES AROUND) IS TIPPED.

17. UNITS FOR MEASURING DISTANCES ASTRONOMICAL UNIT (AU) –THE AVERAGE DISTANCE BETWEEN THE EARTH AND THE SUN –ABOUT 150,000,000 KM –A UNIT OF DISTANCE USED WITHIN THE SOLAR SYSTEM LIGHT YEAR (LY)‏ –THE DISTANCE LIGHT TRAVELS IN ONE YEAR –ABOUT 9.5 x 10 12 KM OR 6333 AU –A UNIT OF DISTANCE USED FOR STARS PARSEC (pc)‏ –ABOUT 3.26 LIGHT YEARS –ANOTHER UNIT OF DISTANCE USED FOR STARS

18. NAMEDistance From Sun MERCURY0.4 AU VENUS0.7 EARTH1.0 MARS1.5 JUPITER5.2 SATURN9.5 URANUS19 NEPTUNE30 ALL PLANETS ORBIT THE SUN IN THE SAME DIRECTION, AND THEIR ORBITS ARE NEARLY IN THE SAME PLANE. THUS, THE SOLAR SYSTEM IS SHAPED LIKE A FLATTENED DISK. PLANETS IN OUR SOLAR SYSTEM

19. SHAPEFLATTENED DISK DIAMETER100,000 LY THICKNESS2,000 LY NUMBER OF STARS400 BILLION ROTATION PERIOD250 MILLION YEARS SUN’S DISTANCE FROM CENTER30,000 LY AVERAGE DISTANCE BETWEEN STARS 5 LY TYPICAL STAR0.5 SOLAR MASSES MILKY WAY GALAXY

22. ACROSS UNITED STATES0.02 SECONDS EARTH TO MOON1.3 SECONDS EARTH TO SUN8 MINUTES ACROSS SOLAR SYSTEMFEW HOURS NEAREST STAR (BEYOND SUN)4 YEARS ACROSS MILKY WAY GALAXY100,000 YEARS NEAREST OTHER MAJOR GALAXY2 MILLION YRS FARTHEST GALAXIES WE CAN SEE10 BILLION YRS LIGHT TRAVEL TIMES

23. WHY EXAMINE STARS? WHETHER OR NOT A PLANET IS SUITABLE FOR LIFE DEPENDS PARTLY ON WHAT KIND OF STAR IT ORBITS. WE NEED TO DECIDE WHICH STARS MIGHT HAVE PLANETS THAT ARE SUITABLE FOR LIFE WE SHOULD THINK ABOUT WHETHER STARS THEMSELVES, AT ANY STAGE OF THEIR “LIFETIMES,” MIGHT BE SUITABLE LOCATIONS FOR LIFE.

24. APPARENT VS. INTRINSIC BRIGHTNESS INTRINSIC BRIGHTNESS DESCRIBES THE AMOUNT OF LIGHT ENERGY THE STAR EMITS PER SECOND. APPARENT BRIGHTNESS IS HOW BRIGHT THE STAR ACTUALLY APPEARS IN THE SKY TO US HERE ON EARTH. WHY ARE THESE DIFFERENT? –THE FARTHER AWAY A STAR IS, THE FAINTER IT APPEARS. –THUS, APPARENT BRIGHTNESS IS DETERMINED BY BOTH INTRINSIC BRIGHTNESS AND DISTANCE. UNLESS I SPECIFY OTHERWISE, WE WILL BE REFERRING TO INTRINSIC BRIGHTNESS WHENEVER WE DISCUSS BRIGHTNESS FROM NOW ON.

25. TEMPERATURE SCALES SCALE ABSOLUTE WATER WATER ZEROFREEZESBOILS FAHRENHEIT-459 32212 CELSIUS-273 0100 KELVIN 0 273373 THE HIGHER THE TEMPERATURE, THE FASTER THE RANDOM MOTION OF INDIVIDUAL PARTICLES. ABSOLUTE ZERO IS THE LOWEST POSSIBLE TEMPERATURE, AT WHICH THIS RANDOM MOTION STOPS. CONVERSION:T IS KELVIN TEMPERATURE T C = T – 273T C IS CELSIUS TEMPERATURE T F = (9/5) T C + 32 T F IS FAHRENHEIT TEMPERATURE

26. PROPERTIES OF STARS THE SUN: MASS: 1 SOLAR MASS = 2 x 10 30 kg = 330,000 EARTH MASSES = 1,000 JUPITER MASSES SIZE: 1 SOLAR RADIUS = 7 X 10 5 km = 110 EARTH RADII BRIGHTNESS: 1 SOLAR LUMINOSITY = 4 x 10 26 W “SURFACE” TEMPERATURE: 6000 K (10,000 o F)‏ COMPOSITION: OTHER STARS: MASS RANGES FROM 1/10 TO 20 SOLAR MASSES SIZE RANGES FROM 1/100 TO 500 SOLAR RADII BRIGHTNESS RANGES FROM 0.000001 (10 -6 or 1 MILLIONTH) TO 1,000,000 (10 6 or 1 MILLION) SOLAR LUMINOSITIES TEMPERATURE RANGES FROM 2,500 K TO 30,000 K (OR 4000 o F TO 50,000 o F), AND IS RELATED TO COLOR 90.99% HYDROGEN 8.87% HELIUM 0.08% OXYGEN 0.03% CARBON 0.02% NEON 0.01% NITROGEN <0.01% EVERYTHING ELSE

27. STELLAR SPECTRA THE LIGHT FROM A STAR CAN BE PASSED THROUGH A PRISM OR DIFFRACTION GRATING TO BREAK IT UP INTO VARIOUS COLORS (OR WAVELENGTHS). ASTRONOMERS CAN THEN MEASURE HOW BRIGHT THE LIGHT OF EACH COLOR IS. THE RESULT IS A SPECTRUM. (PLURAL: SPECTRA)‏ STELLAR SPECTRA SHOW TWO MAIN FEATURES: –AS WE GO FROM SHORT TO LONG WAVELENGTHS (RED TO BLUE), THE BRIGHTNESS GOES UP, REACHES A PEAK, AND THEN GOES BACK DOWN AGAIN. THIS IS CALLED A BLACKBODY SPECTRUM. –THERE ARE DARK LINES AT CERTAIN COLORS, INDICATING THAT LITTLE OR NO LIGHT OF THAT COLOR IS PRESENT. THESE ARE CALLED ABSORPTION LINES. ASTRONOMERS CAN DETERMINE A LOT OF INFORMATION ABOUT A STAR FROM ITS SPECTRUM.

28. BLACKBODY RADIATION THE TYPE OF LIGHT THAT IS EMITTED BY A STAR OR ANY OTHER HOT GLOWING OBJECT THE COLOR OF LIGHT DEPENDS ONLY ON THE TEMPERATURE OF THE OBJECT: – HOTTER OBJECTS ARE BLUER – COOLER OBJECTS ARE REDDER – ROOM TEMPERATURE OBJECTS EMIT IN THE INFRARED THE BRIGHTNESS OF THE LIGHT DEPENDS ON BOTH TEMPERATURE AND SIZE OF THE OBJECT: – FOR OBJECTS OF THE SAME SIZE, HOTTER OBJECTS ARE BRIGHTER COOLER OBJECTS ARE FAINTER – FOR OBJECTS OF THE SAME TEMPERATURE, BIGGER OBJECTS ARE BRIGHTER SMALLER OBJECTS ARE FAINTER

29. Blackbody Spectra

30. MAIN SEQUENCE: THEY FUSE HYDROGEN INTO HELIUM FOR ENERGY. 90% OF STARS ARE THIS TYPE. THEIR SIZE, TEMPERATURE, AND BRIGHTNESS REMAIN RELATIVELY CONSTANT FOR A LONG PERIOD OF TIME (MILLIONS TO BILLIONS OF YEARS). GIANTS AND SUPER GIANTS: THEY FUSE HEAVIER ELEMENTS FOR ENERGY. THEY ARE MUCH LARGER AND MORE EVOLVED THAN MAIN SEQUENCE STARS. MOST ARE RED. WHITE DWARFS, NEUTRON STARS, & BLACK HOLES: “DEAD” STARS, END STAGES OF STELLAR EVOLUTION. SPECTRAL TYPES: O B A F G K M IN ORDER OF HOTTEST TO COOLEST IN ORDER OF BLUEST TO REDDEST SUN IS A G-TYPE MAIN SEQUENCE STAR HERTZSPRUNG-RUSSELL DIAGRAM: PLOT OF BRIGHTNESS vs. SPECTRAL TYPE OR TEMPERATURE TYPES OF STARS

32. DWARFS AND GIANTS RED GIANTS AND SUPERGIANTS ARE BRIGHTER THAN MAIN SEQUENCE STARS OF THE SAME TEMPERATURE. THEREFORE THEY MUST BE LARGER. WHITE DWARFS ARE FAINTER THAN MAIN SEQUENCE STARS OF THE SAME TEMPERATURE. THEREFORE THEY MUST BE SMALLER.

33. ELECTRON ORBITS IN AN ATOM AN ELECTRON IN AN ATOM ISN'T ALLOWED TO BE IN JUST ANY ORBIT. ONLY CERTAIN ORBITS ARE ALLOWED. AN ELECTRON CAN JUMP FROM ONE ALLOWED ORBIT TO ANOTHER ALLOWED ORBIT. THERE IS A SPECIFIC AMOUNT OF ENERGY ASSOCIATED WITH EACH ORBIT. AN ELECTRON IN A LARGER ORBIT HAS MORE ENERGY THAN AN ELECTRON IN A SMALLER ORBIT. WHEN AN ELECTRON JUMPS FROM ONE ORBIT TO ANOTHER, ENERGY MUST BE CONSERVED (CAN'T BE CREATED OR DESTROYED).

34. EMISSION LINES WHEN AN ELECTRON JUMPS FROM A LARGER ORBIT TO A SMALLER ORBIT, IT LOSES ENERGY. THIS ENERGY IS USED TO CREATE A PHOTON, WHICH THEN CARRIES THE ENERGY AWAY. THE PHOTON'S ENERGY IS EQUAL TO THE ENERGY LOST BY THE ELECTRON. ALL PHOTONS EMITTED FOR A PARTICULAR JUMP HAVE THE SAME ENERGY, THUS THE SAME COLOR. THUS THE SPECTRUM HAS AN EMISSION LINE, OR IS BRIGHTER, AT THIS SPECIFIC COLOR. THE ALLOWED ORBITS, AND THUS THE COLORS OF LIGHT EMITTED, ARE DIFFERENT FOR EVERY MATERIAL (ELEMENT OR COMPOUND). THE COLORS OR WAVELENGTHS OF THE EMISSION LINES CAN BE USED TO IDENTIFY THE MATERIAL.

35. ABSORPTION LINES WHEN AN ELECTRON JUMPS FROM A SMALLER ORBIT TO A LARGER ORBIT, IT GAINS ENERGY. THIS ENERGY MUST COME FROM SOMEWHERE, USUALLY BY ABSORBING A PHOTON OF THE APPROPRIATE ENERGY. THE PHOTON'S ENERGY IS EQUAL TO THE ENERGY GAINED BY THE ELECTRON. (IF A PHOTON OF THE RIGHT ENERGY ISN'T AVAILABLE TO BE ABSORBED, THE ELECTRON DOESN'T MAKE THE JUMP.) ALL PHOTONS ABSORBED FOR A PARTICULAR JUMP HAVE THE SAME ENERGY, THUS THE SAME COLOR. THUS THE SPECTRUM HAS AN ABSORPTION LINE, OR IS FAINTER, AT THIS SPECIFIC COLOR. (SOMETIMES ENOUGH PHOTONS ARE ABSORBED TO MAKE THE LINE APPEAR BLACK.)‏ THE ALLOWED ORBITS, AND THUS THE COLORS OF LIGHT ABSORBED, ARE DIFFERENT FOR EVERY MATERIAL (ELEMENT OR COMPOUND). THE COLORS OR WAVELENGTHS OF THE EMISSION LINES CAN BE USED TO IDENTIFY THE MATERIAL.

37. STELLAR SPECTRA THE SPECTRUM OF LIGHT FROM A STAR IS A BLACKBODY (CONTINUOUS) SPECTRUM WITH ABSORPTION LINES SUPERIMPOSED. THE BLACKBODY SPECTRUM COMES FROM THE HOT DENSE GAS JUST BELOW THE “SURFACE.” AS THE LIGHT PASSES THROUGH THE COOLER, LESS DENSE GAS NEAR THE “SURFACE,” CERTAIN WAVELENGTHS ARE ABSORBED, RESULTING IN ABSORPTION LINES. BY EXAMINING THE ABSORPTION LINES, ASTRONOMERS CAN DETERMINE THE COMPOSITION OF THE STAR.