1. Stars and Galaxies

2. Composition of Stars Chemical elements have a characteristic spectrum in a given range of temperatures. The colors and lines in a spectrum of a star indicate the elements that make up the star. Most common element of stars is hydrogen. Helium is the second most common element of stars. Carbon, oxygen, and nitrogen make up remaining mass of stars.

3. Spectroscope We can tell a lot about a star by observing it using a spectroscope. The spectroscope breaks the light from a star into a spectrum. Scientists can look at the spectra of a star and tell its composition, which direction it is traveling, its age, and how fast it is rotating. Stars that are moving away from Earth produce a red shift. The lines are shifted toward the red end of the spectrum.

4. Temperatures of Stars Surface Temperature of a Star is indicated by the star’s color. Blue shine with hottest temperatures > 30,000 C Blue- White10,000-30,000 C White 7,500-10,000 C Yellow-White 6,000- 7,500 C Yellow 5,000- 6,000 C Orange 3,500- 5,000 C Red shine with the coolest temperatures < 3,500 C

5. Blue stars are hotter Blue light has a shorter wavelength, this means it has more energy Red stars are cooler Red light has a longer wavelength, this means it has less energy

6. Sizes and Masses of Stars Stars vary in size and mass. Some dwarf stars are the size of Earth Sun is a medium-sized star. Giant stars can have diameters 1,000 times Sun’s diameter.

7. Constellations A star is a ball of mostly hydrogen and helium gas that shines extremely brightly. Our Sun is a star. Most stars have partner stars. A group of two stars are known as binaries. Ancient Greeks and Romans observed patterns of stars in the sky  CONSTELLATIONS They imagined that the constellations represented mythological creatures. In reality the stars in a constellation may not be near each other. Some famous constellations are Orion, Big Dipper and Ursa Minor.

8. Circumpolar Constellations Circumpolar Stars are always visible in the night sky. As the Earth moves, some constellations, such as Ursa Minor and Ursa Major, and Cassiopeia circle around Polaris or North Star. They appear to complete one full circle in the sky in 24 hours because the Earth rotates. They are visible all year.

9. Stellar Motion Apparent Motion #1 - Earth’s revolution around the Sun causes stars to appear to move - Visible stars appear to shift slightly to west every night - As Earth orbits Sun, different stars become visible during different seasons Apparent Motion #2 - Caused by movement of Earth - Stars appear to move counterclockwise around a central star called Polaris or the North Star - Circular pattern caused by rotation of Earth on axis

10. Actual Stellar Motion Stars rotate on an axis Stars may revolve around another star Stars move away or toward our Solar System

11. Doppler Effect The Light Spectrum of a Star that is moving toward or away from Earth appears to shift. The apparent shift in the wavelength of light emitted by a light source ( the star) moving toward or away from an observer is called the DOPPLER EFFECT. The light from stars is shifted based on the star’s movement in relationship to Earth.

12. Doppler Effect Light from stars that are moving away from Earth is shifted slightly toward the red end of the spectrum. Light from stars that are moving toward the Earth is shifted slightly toward the blue end of the spectrum. When a source of light (like a star) is stationary, the wavelengths of light remain the same distance apart. When a source of light is moving toward you, the wavelengths of light get closer together. This is called blueshift. When a source of light is moving away from you, the wavelengths of light get farther apart. This is called redshift. This is how scientists find out if the universe is growing, shrinking, or staying the same size

13. Doppler Effect The Doppler Effect causes the absorption spectrum of a star to shift toward the red or blue.

15. Distances to Stars Distances between stars and Earth are measured in light-years. A light-year is the distance that light travels in one year. The speed of light is 300,000 km/s Light travels about 9.46 trillion km. per year. The light you see when you look at a star left that star sometime in the past.

16. Parallax We measure how far a star is from the Earth using a method known as parallax. Parallax = the apparent shift in a star’s position when viewed from different locations. Parallax is determined by observing the same star when the Earth is at two different points in its orbit around the Sun. The star’s position relative to more distant background stars will appear to change. This creates an angle which can be measured.

17. Apparent and Absolute Magnitude The absolute magnitude of a star is the amount of light it gives off. The apparent magnitude is the amount of light that is received on earth. A star that is dim can appear bright if it is close to Earth. Magnitude values are assigned to stars. Lower numbers mean brighter stars. While the Sun’s absolute magnitude is 4.8, its apparent brightness is -26, because we are so close.

18. Brightness of Stars The brightness of a star depends on Size Surface temperature Distance from the Earth (absolute and apparent magnitude)

19. The Sun The sun is 150 million kilometers from the Earth. The sun is 4.6 billion years old. The volume of the Sun is 1 million times greater than Earth. The sun’s density is only ¼ of the Earth because the sun is made only of gases.

20. Layers of the Sun Corona (hottest part of outer layers – 1,700,000 degrees C) Chromosphere- (atmosphere 27,800 ºC) Photosphere (surface of the sun, 6000 ºC) at the top of the convective zone The radiative zone is between the core and the convective zone Core- interior of sun- 15,000,000ºC

21. Sunspots Sunspots – cooler than the rest of the sun’s surface they appear as dark spots. Their movement shows that the sun rotates but that the sun rotates more quickly at the equator than the poles. This tells us it does not rotate as a solid object.

22. Solar Flares, Prominences and CME Solar flares – bright bursts of light on the sun’s surface. Twisted loops of gas that originate in the chromosphere are called Prominences. Coronal mass ejections (CME) interfere with communication on Earth.

23. Classifying Stars Astronomers have developed theories about the evolution of stars by studying stars in different stages of development. Astronomers plot the surface temperature of stars against their luminosity, the energy given off each second in a graph called the H-R diagram which describes the LIFE CYLCE of a star.

24. Surface Temperature of Stars The surface temperature of a star can be determined by the color. Blue-white (hottest) – 25,000º C White - 10,000º C Yellow (Sun) - 6,000º C Red-orange- 5,000º C Red (coolest) - 3,000º C

25. The Hertzsprung-Russell H-R Diagram Graph of Temperature vs. Luminosity of stars Temperature on x-axis Luminosity on y-axis As the absolute magnitude of a star increases, the temperature of the star also increases. The exceptions are dying stars like red-giants or white dwarfs.

26. H-R Diagram H-R Diagram describes the Life Cycle of a star Highest temperatures are plotted on the left of x-axis Highest luminosities are plotted on the top of y -axis

27. H-R Diagram The temperatures and luminosities for most stars falls within a band that runs diagonally through the middle of the H-R diagram. Band extends from cool, dim, red stars at the lower right to hot, bright, blue stars at the upper left  known as Main Sequence. Stars within this band are called main sequence stars. ie. Sun

28. Why do stars shine? In the main sequence of a stars life, 96-99% of the star’s composition is hydrogen and helium. Due to the extreme mass of the Sun, within the core of a star, gravitational forces cause nuclear fusion. Four hydrogen atoms are fused to produce one helium atom. The remaining matter is given off in the form of heat and light energy.

30. Star Formation A star begins as a nebula, a cloud of gas and dust. 70% hydrogen, 28% helium, 2% heavier elements. Outside force ( like explosion of star ) compresses cloud of gas, particles move closer to each other and bulled together by gravity. Regions of dense matter build up Newton’s Law of Universal Gravitation = all objects in universe attract each other though gravitational force.

31. Protostars Gravity makes dense regions of matter more compact Protostar is central concentration of matter Gravitational energy converted to heat and temperature of protostar increases. Continues over several million years Plasma forms; Plasma is a hot, ionized gas consisting of free moving positive ions and electrons.

32. A Star is Born Protostar temperature increases to 10,000,000 C and nuclear fusion begins Nuclear Fusion occurs at extremely high temps and pressure cause atomic nuclei to combine to form larger nuclei and enormous amount of energy are releases Hydrogen fuses into helium. Process can continue for billions of years.

33. Main Sequence Stage Second and longest stage in the life of a star During this stage, energy continues to be generated a s hydrogen fuses to helium A star enters its third stage when almost all of the hydrogen atoms in its core have fused to helium atoms. Without hydrogen fuel, the core of the star contracts under the force of its gravity. Outer shell of the star expands greatly.

34. Giant Stars As the star expands, the star’s shell of gases grows cooler Stars glow as large red stars called red giants. As these stars become larger, more luminous and cooler, they move off the main sequence. Giant stars are above the main-sequence on the H-R diagram.

35. Final Stages of a Sunlike Star As star’s outer gases drift away, remaining core heats these expanding gases. Planetary nebula is a cloud of gas that forms around a sunlike star that is dying.

36. White Dwarf As planetary nebula disperses, gravity causes remaining matter of the star to collapse inward. A hot, extremely dense core of matter – a white dwarf – is left. White dwarfs shine for billions of years before they cool completely. White dwarfs are hot but dim in lower left of H-R diagram. Final stage of life. White dwarf that no longer gives off light becomes a black dwarf.

37. Novas and Supernovas Nova – a star that suddenly becomes brighter; large explosion as a white dwarf revolving around a red giant captures gases ( binary system ); pressure builds up and explosion occurs. Supernova – a white dwarf in a binary system that has a tremendous explosion and blows itself apart.

38. Final Stages of Massive Stars Only a small percentage of white dwarfs become supernovas. However, massive stars become supernovas as part of their life cycle.

39. Neutron Stars and Pulsars A neutron star is a massive star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons. Neutron stars rotate very rapidly. A pulsar is a rapidly spinning neutron star that emits pulses of radio and optical energy.

40. Black Holes A black hole is an object so massive and dense that even light cannot escape its gravity Black holes can be observed by its effect on a companion star – matter of the companion star is pulled into the black hole. Matter that is absorbed becomes so hot that it emits X-rays that can be detected.

41. Size of Stars Neutron star- A dying high mass star that is16 km in diameter. White dwarf star- This is a dying low to medium mass star which is earth sized, but can be as small as Asia. Medium sized star- This low to medium mass star at birth is 1/10 to 10 times the size of the Sun. Giant star-This high mass star at birth is 10-100 times our Sun. Super giant star- This very high mass star at birth is100-1000 times the size of our Sun.

42. Evolution of a Star New stars are born from the gases in a nebula. When hydrogen in the cloud reaches a certain temperature (15,000,000 degrees C), nuclear fusion begins. A protostar, or new star, is formed. The main factor that shapes the evolution of a star is the mass it began with. A more massive stars have a shorter life.

43. Evolution of Stars Low to Medium Mass -nebula- main sequence- red giant- white dwarf- black dwarf High Mass -nebula- main sequence- red giant- supernova-neutron star and nebula Very High Mass- nebula- main sequence- red giant- supernova- black hole and new nebula

44. Nebulae A nebula is a massive cloud of dust and gas. Nebulae are the birthplace of new stars. Stars are held together by gravity in galaxies. There are three main types of galaxies, spiral, elliptical and irregular.

45. Spiral Galaxies Galaxies contain various star groups. Most galaxies are spiral galaxies. Spiral galaxies are shaped like pinwheels.

46. Elliptical Galaxies Galaxies that vary in shape from nearly spherical to flat disks are called elliptical galaxies. They contain very little dust and gas. They are usually older.

47. Irregular Galaxies Irregular galaxies have no definite shape.

48. The Milky Way Galaxy The Milky Way Galaxy is a spiral galaxy. Most of the older stars in the Milky Way are found near the nucleus of the galaxy. The Milky Way is estimated to be 100,000 light-years in diameter and about 15,000 light-years thick. The Sun is located in one of the pinwheel arms. The stars rotate counter clockwise around the center. This takes 200 million years.

49. Theories of Universe Formation The first theory about the Universe was known as the Steady State Theory. This theory stated that the universe was always the same. Astronomers believe that the expanding universe is the result of an enormous explosion known as the big bang. The explosion occurred 15-20 billion years ago. As the matter moved away from the explosion, gravity caused clusters to form. These clusters became the galaxies of the universe. Support comes from Red Shift and background radiation.