Chapter 28 – Stars and Galaxies

1. Chapter 28 – Stars and Galaxies • Page 610 • Why is this galaxy so bright? • What shape is this galaxy? • How do we obtain images like this?

2. Chapter 28.1

3. A Closer Look at Light

4. What is light? • Light is a form of electromagnetic radiation (EM)

5. Other types of EM listed from longest to shortest wavelengths • Radio • Microwave • Infrared • Visible light • Ultraviolet • X-rays • Gamma rays • This is known as the EM spectrum

6. All EM energy travels in waves and at the speed of light • Can travel through empty space (vacuum)

7. Spectroscope • Visible white light is actually made up of light of various colors each with a different wavelength • The various color can be observed • In a rainbow • Passing light through a prism • Or an astronomers instrument known as a spectroscope

8. The colors ROY G. BIV are aligned from longest to shortest (violet) • Longer wavelengths refract less

9. Chapter 28.2

10. Types of spectra from spectroscopes • Continuous spectrum – unbroken band of colors which are emitted by • Glowing solids (filament) • Glowing liquids (molten iron) • Hot compressed gases (inside stars)

11. Emission spectrum – lines of different colors • Produced by glowing thin gases • Each element has its own spectra therefore scientists can identify the gas

12. Absorption spectrum – a continuous spectrum crossed by dark lines • Elements in the thin gas that surround a star absorb the same wavelength they would emit • The stars absorption spectrum indicates the composition of the stars outer layer

13. The sun radiates a continuous spectrum, however, the gases in the atmosphere absorb some wavelengths. By analyzing the absorbed bands, scientists can figure out the composition of the sun’s outer layer. • Absorption spectrum can also determine a planets atmosphere

14. Doppler Effect • By observing how the spectral lines are shifting, scientists can tell how a star is moving compared to the earth • Move to the red end, “red shift,” the star is moving away • Move to the blue end, “blue shift,” star is getting closer • By using spectrums from the lab and the stars, they can determine how fast they are moving

15. Chapter 28.3

16. Stars and Their Characteristics

17. Constellations – name given to groups of stars • There are 88 of them • Big dipper – best known asterism (small star grouping) is actually part of a larger grouping known as Ursa Major • We can use the dipper to find other constellations

18. The stars appear to move in two ways • Nightly variation – due to earth’s rotation • Yearly due to earth’s revolution • Orion – winter constellation • Lyra – summer constellation

20. Apparent magnitude • Is the brightness of the star as seen from earth • The lower the number, the brighter it is • Sun is –26.7 • Faintest is +6

21. Distance to stars • Astronomical Unit (AU) distance from earth to sun – 150 million km • Proxima Centauri – next nearest star is 260,000AU • Therefore, astronomers use light-years – a unit of measure that light travels in one year. • Light travels about 300,000km/sec  1 year = 9.5×1012 • Proxima Centauri is about 4.2 light years away

22. Elements in Stars • Stars are mostly of super-hot gases – mostly H & He

23. Mass, Size and Temperature of Stars • Mass is something that can not be observed directly. It can only be calculated based on other observations • Stellar mass is expressed as multiples of the sun’s mass • Betelgeuse’s mass – 20 solar masses

24. Temperature and Color • Blue stars are hot • Red stars are cool

25. Luminosity • The actual brightness of the star is luminosity • If two stars have the same surface temperature, the larger star would be more luminous • If the same size, hotter one would be brighter • Types of magnitude • Absolute – as if all stars were same distance from earth • Apparent – as they appear in the nighttime sky

26. Variable Stars • Some stars show regular variation of brightness over cycles that last from days to years • Cepheid Variables – yellow supergiants whose cycles range from 1 to 50 days • If a Cepheid is located in another galaxy, astronomers can find the distance to these galaxies by comparing absolute and apparent magnitudes • Other stars change in brightness because they revolve around another star. This is known as a ‘binary star system.’

27. Chapter 28.4

28. Life Cycles of Stars

29. Hertzsprung-Russel Diagram • A diagram to help explain a stars life • Most stars fall into 4 distinct groups • Main sequence – 90% of stars • Our sun • Giants – 10-100x bigger than our sun – more luminous • Supergiants – more than 100x bigger than our sun • White dwarves – stars near the end of their lives

30. Birth of a Star • Stars begin their life as a nebula • Huge cloud of gas

31. Death of a Star • 2 paths • Nebula  protostar  main sequence  red giant  planetary nebula  white dwarf • Nebula  protostar  massive star  red supergiant  supernova  blackhole or neutron star • Our sun will swell into a red giant, then its outer layers will get blown away and only an earth-sized fiery hot carbon-oxygen core will remain (white dwarf)

32. Remnants of Massive Stars • Massive star goes supernova, the core that is left behind is so massive that the electrons of elements are pulled into the nucleus forming a neutron star. • Some neutron stars spin rapidly, burst of radio waves, these are known as pulsars • Black hole – so dense that their gravity will not even let light escape

33. Chapter 28.5

34. Galaxies and the Universe

35. What are galaxies • A system of millions of stars that appear as a single star in our sky • There is between 50-100 billion galaxies • There are millions of light years between galaxies • Sun belongs to the Milky Way Galaxy which is a spiral galaxy • Milky Way belongs to the Local Group of about 30 galaxies

36. Types of galaxies • Spiral – like the Milky Way • Elliptical – spherical to lens shaped • Irregular – much smaller and fainter with no shape

37. Active Galaxies • Galaxies that emit more energy than their combined stars are said to be active • Currently it is thought that super massive black holes are at the center of these galaxies