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  1. 1. • How many galaxies do you think are there in the universe?• Is it possible for us to circumnavigate our own galaxy?• Do you think that there is also another “Earth” somewhere out there?
  2. 2. RT Grouping• KWL Technique
  3. 3. RT Grouping• KWL Technique
  4. 4. • Types of Galaxies• Common Galaxies• Location of our Solar System in the Galaxy• Great Nebula of Andromeda• Quasars• Clouds of Magellan (Large and Small Magellanic Cloud)
  5. 5. • Elliptical galaxies are smooth and elliptical in appearance.• Most common type of galaxy• There are four distinguishing characteristics of the ellipticals:(a)they have much more random star motion than orderly rotational motion (star orbits are aligned in a wide range of angles and have a wide range of eccentricities)(b) they have very little dust and gas left between the stars;
  6. 6. (a) this means that they have no new star formation occuring now and no hot, bright, massive stars in them (those stars are too short-lived); and(b) they have no spiral structure.
  7. 7. • Spiral galaxies have flattened disks with a spiral pattern in the disk.• The spiral arms can go all of the way into the bulge or be attached to the ends of a long bar of gas and dust that bisects the bulge.
  8. 8. • The four distinguishing characteristics of the spirals are: (a) they have more orderly, rotational motion than random motion (the rotation refers to the disk as a whole and means that the star orbits are closely confined to a narrow range of angles and are fairly circular);(b) they have some or a lot of gas and dust between the stars;(c) this means they can have new star formation occuring in the disk, particularly in the spiral arms; and (d) they have a spiral structure.
  9. 9. • Spiral galaxies are sub-classified into ``a, ``b, ``c, and ``d groups according to how loose their spiral arms are and how big the nucleus is.• The ``a group spirals have large bulges and very tightly wound spiral arms and the ``d group spirals have almost no bulge and very loose arms.
  10. 10. • The Milky Way is between the ``b and ``c groups with a bar, so it is an SBbc-type spiral galaxy. Most spirals are luminous. Some other examples of spiral galaxies are M31 (the Andromeda Galaxy) and M33 (a small spiral in the Local Group).
  11. 11. • Irregular galaxies have no definite structure.• The stars are bunched up but the patches are randomly distributed throughout the galaxy.• Some irregulars have a lot of dust and gas so star formation is possible. Some are undergoing a burst of star formation now, so many H II regions are seen in them.• Others have very little star formation going on in them (even some of those with a lot of gas and dust still in them).
  12. 12. • Most irregulars are small and faint.• The dwarf irregulars may be the most common type of galaxy in the universe (or maybe the dwarf ellipticals are).• The estimates of the number of dwarf irregulars and dwarf ellipticals are based on the proportions of these types of galaxies in nearby groups.
  13. 13. • The dwarf galaxies far away are too faint to be seen and are, therefore, overlooked in surveys of the sky. Perhaps if the dwarf galaxies were brighter, Hubble would have arranged the galaxies in a different sequence instead of the two-pronged sequence.• Examples of irregular galaxies are the Large and Small Magellanic Clouds (two small irregulars that orbit the Milky Way).
  14. 14. • What are the types of galaxies?• What is the most common type of galaxy?• What type of galaxy is the Milky Way?• Describe an Elliptical Galaxy.• Describe a Spiral Galaxy.• Describe an Irregular Galaxy.
  15. 15. GALAXY DESCRIPTION This is the galaxy thatMilky Way contains Earth, it is named after the nebulosity in the Galaxy night sky that marks the densest concentration of stars of our galaxy in the sky, which appears to blur together into a faint glow, called the Milky Way.
  16. 16. GALAXY DESCRIPTION Commonly just Andromeda,Andromeda this, called the Andromeda Galaxy, Andromeda Nebula, Great Andromeda Nebula,Andromeda Spiral Nebula, and such, has been traditionally called Andromeda, after the constellation in which it lies.
  17. 17. GALAXY DESCRIPTION This is the fourth largest Large galaxy in the Local Group, and forms a pair withMagellanic the SMC, and from recent Cloud research, may not be part of the Milky Way system of satellites at all. It is visible with the naked eye.
  18. 18. GALAXY DESCRIPTION This forms a pair with Small the LMC, and fromMagellanic recent research, may not be part of the Milky Cloud Way system of satellites at all. One of the four irregular galaxies
  19. 19. • Our home lies within the disk of the Milky Way. Its the disk where most of the galaxys gas and dust is located.• As a result this is where most new stars are being born. Just as the Earth has an equator, so too does the galaxy and we are about 14 light years above whats called the equatorial symmetry plane.
  20. 20. • As to the thickness of the disk, most current estimates put it at around 1,000 light years thick. Obviously our solar system lies very close to the galaxys equator.• As to our distance from the center of the galaxy, the best guess is that we are 26,000 to 28,000 light years from the center.
  21. 21. • The estimates vary due to uncertainty in the exact size of the galaxy and the time it takes the solar system to complete one orbit of our galaxy.
  22. 22. • The yellow circle in the picture shows the orbital path of our solar system as it travels around the center of the Milky Way. The red dot, located just above the r in the arm associated with the Orion Arm shows our current location on this path.
  23. 23. • Which part of the Milky Way Galaxy is our Solar System located?
  24. 24. • A quasi-stellar radio source ("quasar") is a very energetic and distant active galactic nucleus.• Quasars are extremely luminous and were first identified as being high red shift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies.
  25. 25. • Quasars have all the same properties as active galaxies, but are more powerful: the irradiation is partially nonthermal (i.e., not due to a black body), and approximately 10 percent are observed to also have jets and lobes like those of radio galaxies that also carry significant (but poorly known) amounts of energy in the form of high energy (i.e., rapidly moving, close to the speed of light) particles (either electrons and protons or electrons and positrons).
  26. 26. • The energy radiated by the quasar is about a thousand times more than that of a normal galaxy.• The brightness of a quasar varies over periods of days or years.• Astronomers believe that quasars are eruptions at the center of large galaxies.• They get their energy from a black hole.
  27. 27. • A black hole is created when an old star collapses.• It is a region in space with tremendous gravity.• A body pulled by this gravity gets large amount of energy.
  28. 28. RT Grouping• KWL Technique
  29. 29. • What are the different types of galaxies?• What type of galaxy is the Milky Way?• Which part of the Milky Way Galaxy is our Solar System located?
  30. 30. Answer page 283 of your Science book