STARS

1. STARS

2. Characteristics of Stars • Groups of stars that form patterns in the sky are called constellations • Example: Ursa Major (Big Dipper), Ursa Minor (Little Dipper), and Orion • The last two stars in Ursa Major’s “dipper” can be used to find Polaris (North Star) • Polaris is located directly above the North Pole (90º), and is only visible in the northern hemisphere

4. Circumpolar Constellations • Because of the Earth’s rotation, the constellations appear to move • If the constellations appear to move around Polaris, they are called circumpolar constellations • The constellations Ursa Major and Minor are both circumpolar constellations • Using time exposure photography, the apparent motion of the stars around Polaris can be recorded as circular trails

8. The positions of the constellations as viewed from Earth changes fromseason to season • This is caused by the change in Earth’s position in its orbit around the sun • Example: Orion the Hunter is a winter constellation

11. Physical Properties of Stars • Stars differ in size, density, mass, composition, and color • The color of a star is determined by it surface temperature (Reference Tables) • The hotter the star, the bluer the color. The cooler the star, the redder the color. • The sun is a yellow star

13. Physical Properties of Stars • Most stars are made up of mostly hydrogen and helium (approx. 98%) • The remaining 2% may be other elements • A spectrum analysis of the star can tell us what elements a star is made of, since the radiated spectrum depends on a star’s composition and temperature

14. ApparentMagnitude • How bright a star appears on to us on Earth • The farther a star is from Earth, the dimmer it will look even though it may actually be a very bright star • Because of this, apparent magnitude does not tell the true brightness of a star

15. Luminosity • The actual (true) brightness of the star • Depends on the size and temperature of the star • Hotter stars are more luminous (brighter) than cooler stars • If the temperatures are the same, a larger star will be more luminous

16. Absolute Magnitude • The luminosity of the stars if they all were the same distance from Earth • aka – picture all the stars lined up the same distance from Earth, then compare their brightness • This is the most useful when comparing the brightness of the stars

18. Distances to the Stars

19. The sun is the closest star to Earth • It is approx. 150,000,000 km (93,000,000 miles) from the Earth • This distance is called an astronomical unit (AU) • The closest star to Earth, after the sun, is Alpha Centuri • It is 300,000 times farther away from Earth than the sun. Because of the great distances in space, larger units of measure must be used • The light-year is the distance that light travels in one year • Since light can travel 300,000 km/sec (186,000 miles/sec), light travels 9.5 trillion km/year!!! • Alpha Centuri is 4.3 light-years from Earth!

20. Star Formation& Origin

21. large clouds of dust and gas in space are the basic materials needed for star formation • the majority of this gas is hydrogen • some outside force causes the cloud to be pushed together • as the gas and dust get closer, friction between the particles causes the temperature to increase • the attraction of gravity between the particles causes them to continue to move together, and density also increases

22. friction increases and temperature increase until the center becomes so hot that nuclear fusion takes place • hydrogen atoms are forced together to form helium atoms, and energy is released • In a nuclear reactor like Indian Point, nuclear fissiontakes place • This is when radioactive atoms are split apart to release energy

23. But where does the gas & dust come from????

24. SUPERNOVAS • One of the most energetic explosive events • occur at the end of a star's lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy • If the star is particularly massive, then its core will collapse and in so doing will release a huge amount of energy • This will cause a blast wave that ejects the star's envelope into interstellar space

25. Etna Carinae Supernova remnant Supernova rings

26. SUPERNOVA 1987 – right image is the star that became the left image after going supernova – shone brighter than most galaxies for a few months!

27. NEBULA • Clouds of dust & gas (supernova remnants?) • 2 Main Types: • Diffuse Nebula – nearby star illuminates the gas/dust cloud • Dark Nebula – Dark patch against more-distant stars (dust/gas is blocking the light from stars behind it)

28. ORION NEBULA VEIL NEBULA HELIX NEBULA KEYHOLE NEBULA

29. CAT’S EYE NEBULA

30. ESKIMO NEBULA 5000 LY FROM EARTH - 10,000 YRS OLD

31. CRAB NEBULA

32. HORSEHEAD NEBULA – PART OF ORION

34. A STAR IS BORN… I WANT MY MOMMY!!

35. THE BIRTH OF A STAR (OOH IT’S A GIRL!) STELLAR NURSERY GLOBULE GLOBULE COLLAPSE PROTOPLANETARY DISK & CORE DUST & GAS COMPRESS DUE TO GRAVITATIONAL FORCES, FORMING A SLOWLY ROTATING GLOBULE GRAVITY BECOMES TOO STRONG & THE GLOBULE COLLAPSES, SPINNING INCREASES A STAR BEGINS TO FORM IN A NEBULA (CLOUD OF GAS & DUST) SPIN, PRESSURE, & TEMPERATURE INCREASE, PLANETS ARE FORMED, AND CENTRAL CORE (SUN) FORMED

36. LIFE CYCLE OF STARS • A star’s life cycle is determined by its MASS • The larger the star, the faster it burns out! • A star’s MASS is determined by the MATTER available in the nebula of formation

37. LIFE CYCLE OF STARS SUN-LIKE STARS (UP TO 1.5 X MASS OF OUR SUN) RED GIANT PLANETARY NEBULA WHITE DWARF BLACK DWARF STELLAR NURSERY MASSIVE STARS (1.5 – 3 X OUR SUN) RED SUPERGIANT SUPERNOVA NEUTRON STAR STARS FORM IN A NEBULA OF GAS & DUST SUPERMASSIVE STARS > 3 X OUR SUN RED SUPERGIANT SUPERNOVA BLACKHOLE

38. DEATH OF A SUN-LIKE STAR SUN-LIKE STAR RED GIANT PLANETARY NEBULA WHITE DWARF BLACK DWARF STAR COOLS ARE SHRINKS BECOMING ONLY A FEW THOUSAND MILES ACROSS! NO NUCLEAR REACTION LONGEST, MOST STABLE PERIOD OF A STAR’S LIFE – CONVERTS HYDROGEN TO HELIUM, RADIATING HEAT & LIGHT STAR LOSES ALL HEAT TO SPACE AND BECOMES COLD AND DARK NUCLEAR FUEL DEPLETES, CORE CONTRACTS, SHELL EXPANDS OUTER LAYERS DRIFT OFF INTO SPACE IN SPHERE-LIKE PATTERN

40. THE STAR SOL: OUR SUN

41. Handy Dandy Earth Science Reference TablesPage 15

42. H-R DIAGRAM

43. Properties of the Sun • average size yellow star • fairly cool compared to other stars • diameter is approx. 110 times larger than Earth’s, with a volume that hold more than 1,000,000 Earths. • Light traveling from the sun takes approx. 8 minutes 20 seconds to reach Earth! • surface temperature is approx. 5,500 C and its interior temperature is believed to be 15,000,000 C!!

45. Sunspots & Prominences • Sunspots are regions of intense magnetic fields • Sunspot temperatures are cooler than the photosphere, which makes them appear as dark spots • Prominences are regions along a magnetic field line where conditions are right for light to be emitted • Huge, arching columns of gas often appearing above sunspots

48. Solar Flares • Occasionally, kinks and stresses occur on magnetic field lines discharging amounts  of energy (known as Solar Flares) • The amount of energy released is equivalent to a 2 billion megaton bomb • Flares release large numbers of particles into the corona

50. Source of the Sun’s Energy • The process of NUCLEAR FUSION • Einstein explained this process as E = MC² (matter can be converted into energy) • The hydrogen molecules that the sun is made of fuse together to form a helium atom. When this occurs, energy is given off! • **It is estimated that the sun has enough mass for nuclear fusion to continue for 5 billion more years!