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Stars

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Transcript

• 1. stars Parallax and Magnitude
• 2. 2p 1AU 1AU 61Cygni To distant star p p
• 3.
• A Star with a parallax of 1 arc-second is
• 1 parsec from the Earth
• 1 par ( allax) sec ( ond )
• 4.
• Distance ( pc ) = 1 .
• Parallax ( s )
• 5. 61 Cygni is 0.3 seconds of arc
• Distance = 1
• 0.3
• = 3.33 pc from Earth.
• 6. Consider a star 1 parsec from Earth
• 7. 1AU CIRCUMFERENCE=60 X 60 X 360 AU
• 8. 1 PARSEC CIRCUMFERENCE = 2 Ï€ parsec
• 9.
• So 2 Ï€ parsecs = 60 x 60 x 360 AU
• 1 parsec = 5 x 10 AU
• 10.
• = 3.26 LIGHT YEARS
• 61 Cygni is 3.33 x 3.26 Light Years
• 11. About 11 Light Years away
• 12. Looking At Brightness
• Using the inverse square law
• 13.
• Observed Brightness 1 .
• Area
• 1 .
• distance Â²
• 14.
• Magnitude
• 15. Ancient Greeks
• Brightest stars = Magnitude 1
• Dimmest stars = Magnitude 6
• 16. 19 th CENTURY LIGHT from a magnitude 1 star was 100 times brighter than from a magnitude 6 star.
• 17.
• A Difference of 5 magnitudes
• Corresponds to a ratio of 100
• 18.
• Since
• 2.5 x 2.5 x2.5 x 2.5 x 2.5 = 100
• A Difference of 1 magnitude
• Corresponds to a ratio of 2.5 in the measured intensity of light
• 19.
• The Sun has a magnitude of -26.7
• The dimmest star using a giant telescope + 25
• Naked eye +6
• 20. PROBLEMS
• How bright a star is ( apparent magnitude)
• Doesnâ€™t tell us how bright a star really is.
• Why not ?
• 21.
• It may be brighter, but distant
• It may be dimmer ,but closer.
• Stars are not all the same!
• 22. ABSOLUTE MAGNITUDE
• Defined as equal to the apparent magnitude the star would have at a distance of 10 parsecs from Earth.
• 23.
• The absolute magnitude of stars ranges from â€“ 10 to +15
• 24.
• Absolute Magnitude = M
• Apparent magnitude = m
• Distance = d
• M = m â€“ 5 log d
• 10
• 25. Sirius
• Apparent magnitude â€“ 1.46
• distance = 2.65 parsecs from Earth.
• Absolute Magnitude M = - 1.46 -5 log(0.265)
• = - 1.46 â€“ 5( -0.58)
• = - 1.46 + 2.9
• = 1.44
• 26.
• 27.
• Period = 5.75 days
• Magnitude increases at twice the rate it falls.
• Magnitude changes by 0.7
• Hence intensity ratio =
• = 1.9
• 28.