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  • 1. The Stars: Characteristics, Magnitude, Stellar Classifications, H-R Diagram, Motions and Significance Laver Joy Lovido Marjonlien A. Mahusay
  • 2. Characteristics of stars • Size • Color • Temperature • Composition • Brightness
  • 3. Size of a Star anywhere from 20km to 1 trillion km in diameter Main Group by Star 1. Neutron Star • **Can be the distance you travel to school 2. White Dwarf Star • **Can be the size of Asia 3. Medium-sized Star • **Our own Sun
  • 4. 4. Giant Star • *The diameter 10 to 100X larger than our sun 5. Super-giant Star • *The diameter 1000X larger than sun Size of a Star
  • 5. Color: star can be Blue, White, Orange or Yellow, red Temperature: Blue – hottest (35000⁰C) Yellow – our Sun (5500⁰C) Red - coolest(3000⁰C) Color and Temperature
  • 6. Characteristics of stars Color: stars can be red, blue, white, orange or yellow Composition: contain different elements determined using spectra • Temperature: Blue is the hottest (35000 C) Yellow (our sun) (5500 C) Red is the coolest (3000 C)
  • 7. Composition Astronomers use a spectroscope to determine what stars are made of by their spectral lines • Hydrogen (70% of the total mass of a star ) • Helium (28% of the total mass of a star) • Trace Elements- O, Ne, C, N and other elements (2% )
  • 8. Magnitude of Star 1. Apparent magnitude 2. Absolute magnitude
  • 9. Magnitude of Star 1. Apparent magnitude  is the brightness of a star when viewed from Earth  The lower the number on the scale, the brighter the star appears to us. factors :  how big it is  how hot it is  how far away it is.
  • 10. Analyzing the Apparent Magnitude of Stars Relating Magnitudes to Brightness Ratio Magnitude Difference Ratio of Brightness 1 2.512:1 2 2.5122 = 6.31:1 3 2.5123 = 15.85:1 4 2.5124 = 39.8:1 5 2.5125 = 100:1 . . . 10 2.51210 = 104:1
  • 11. EXAMPLE: Suppose stars 1 & 2 have magnitudes of m1=6 m2= 1: the ratio of their brightness is: SOLUTION: =2.512m1-m2 =2.5126-1 =100.02
  • 12. Analyzing the Apparent Magnitude of Stars • Most powerful telescopes can detect stars with apparent magnitude of +29 • Faintest star seen by eye has apparent magnitude of +6 • This is called a 6th magnitude star
  • 13. 2. Absolute Magnitude the actual brightness of a star, assuming all stars were set at a standard distance from Earth. true brightness  If sun was 32.6 light-years away, it would be 5th magnitude •So absolute magnitude of sun = +5 •Most stars are between -5 and +15 Magnitude of Star
  • 14. Analyzing the Absolute Magnitude of Stars Relating Absolute Magnitude to Luminosity Absolute Magnitude Approximate Luminosity in Solar Units -5 10,000 0 100 5 1 10 0.01
  • 15. EXAMPLE: If Sirius A has Absolute Magnitude of 1.5, how many times that sirius is brightre than the sun? SOLUTION: 5-1.5=3.5 2.5123.5 = 25
  • 16. Comparison of the Nearest Stars in terms of Apparent and Absolute Magnitude Name Distance (ly) Apparent Visual Magnitude AbsoluteVisual Magnitude Sun -26.8 4.83 ProximaCentauri 4.23 11.09 15.5 Alpha CentauriA 4.35 0.01 4.4 B 4.35 1.34 5.7 Barnard’s Star 5.98 9.55 13.2 Wolf359 7.80 14.45 16.6
  • 17. Stellar Classification
  • 18. 1. Color 2. Temperature 2. Size 3. Brightness Stellar Classification
  • 19. Analyzing Starlight The surface temperature of a star is indicated by its color. Blue stars shine with the hottest temperatures and Red stars with the coolest.
  • 20. Stellar Classification • The luminosity class is added in Roman numerals after the temperature spectral class. – Indicates the size of the star. Stellar Luminosity Classes Class Description I Supergiants II Bright Giants III Giants IV Subgiants V Main-sequenceStars VI Subdwarfs VII WhiteDwarfs
  • 21. Getting Familiar to the Spectral Sequence Spectral type- a way of classifying a star by the lines that appears in its spectrum; it is related to surface temperature. Basic spectral types are designated by letters :  OBAFGKM with O for the hottest and M for the coolest.  subdivided with numbers from 0-9
  • 22. Spectral classes are as follows: Oh Be A Fine Girl/Guy, Kiss Me!
  • 23. BrightestStar Name Distance (ly) Spectral type Luminosity Class Apparent Magnitude Absolute Magnitude Sirius 8.6 A1 V -1.44 1.4 Canopus 310 F0 Ib/II -0.74 -5.65 Rigel Kentaurus 4.4 G2 V -0.01 4.3 Arcturus 36.7 K2 III -0.05 -0.31 Vega 25.3 A0 V 0.03 0.58 Capella 42 G8 III 0.08 -4.8
  • 24. Hertzsprung-Russsell Diagram developed by Einar Hertzsprung and Henry Russell in the early 20th century.  graph that exhibits the intrinsic stellar properties such as the sizes, colors and temperatures Plots the individual stars as points , with stellar luminosity on the vertical axis and surface temperature con the horizontal axis
  • 25. Hertzsprung-Russsell Diagram
  • 26. Stellar Motion
  • 27. Stellar Motion Two kinds of motion are associated with stars • 1. APPARENT MOTION • Earth’s rotation causes the illusion of stars moving around a central star, Polaris, commonly known as the North Star. • Earth’s revolution around the Sun causes stars to be visible during different seasons. • The apparent change of position of a star on the celestial sphere is called the proper motion of the star. • Angular Motion on the Celestial Sphere • -Proper motion is usually denoted by the Greek symbol "mu", and is a velocity that is usually quoted in units of seconds of arc per year.
  • 28. Stellar Motion
  • 29. 2. ACTUAL MOTION – First, they move slightly across the sky (only see the closest ones). – Second, they may revolve around another star (binary system). – Third, they may either move away from or toward our solar system. • The apparent shift in the wavelength of light emitted by a light source moving away from or toward an observer is called the Doppler Effect. – Also used for sound waves on Earth. Stellar Motion
  • 30. Stellar Motion
  • 31. Significance of Stars
  • 32. Why is it important to learn about the stars? 1. studying stars is important because it helps tell us how we got all the other elements that make up things around us (and in us!). 2. To learn from other stars may help us understand our own Sun, which is also a star. The Sun only seems different to us because it is so much closer to us than other stars.
  • 33. 3. we can also learn something about how they are born and die. This helps us understand how our own solar system was formed. 4. Stars contain a large fraction of all the visible mass in galaxies. As a result, their combined gravitational forces affect the 'dynamics' of galaxies, i.e. the ways in which galaxies move and evolve in shape.
  • 34. The gravitational pull of one particular star, our Sun, is especially important since it is the Sun's gravitational attraction that keeps the Earth in orbit. -Scott Sandford -Astrophysics Branch -NASA/Ames Research Center