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Charles Hakes Fort Lewis College 1 Charles Hakes Fort Lewis College 2 Chapter 10 Measuring the Stars Parallax and Magnitudes Charles Hakes Fort Lewis College 3 Misc notes • sunspots radiate less energy – overall activity radiates more. • magnetic fields disrupt convection • remove folder debris Charles Hakes Fort Lewis College 4 Chapter 10 Measuring the Stars Charles Hakes Fort Lewis College 5 Magnitude • Historical Magnitude Scale • Hipparcos/Ptolemy • The brightest stars were “of the first magnitude” • Dimmer stars were second, third, etc. magnitude. • Dimmest stars were 6th magnitude Charles Hakes Fort Lewis College 6 Magnitude • Modern Apparent Magnitude scale • A difference of five magnitudes corresponds to exactly a factor of 100 in brightness. • One magnitude is a factor of 1000.2 = 2.511886 • Both negative and positive magnitudes are allowed. • Sun -26.8 • Sirius -1.4 • Faintest stars visible in Durango ~6.5 • Magnitudes don’t have to be integers. Charles Hakes Fort Lewis College 7 More Precisely 10-1 More on the Magnitude Scale • Note relative brightness on the left, and magnitude on the right. Charles Hakes Fort Lewis College 8 Review Charles Hakes Fort Lewis College 9 Which is the net result of the protonproton chain? A) 4 protons = 1 helium 4 + 2 neutrinos + energy B) 2 protons = deuterium + a positron + an antineutrino + energy C) 4 protons = 2 helium-2 + 2 positrons + energy D) 6 protons = 2 heliums + 3 positrons + 3 neutrinos + energy E) only energy Charles Hakes Fort Lewis College 10 Which is the net result of the protonproton chain? A) 4 protons = 1 helium 4 + 2 neutrinos + energy B) 2 protons = deuterium + a positron + an antineutrino + energy C) 4 protons = 2 helium-2 + 2 positrons + energy D) 6 protons = 2 heliums + 3 positrons + 3 neutrinos + energy E) only energy Charles Hakes Fort Lewis College 11 What evidence do we have for solar convection? A) sunspot polarity B) the Zeeman effect C) neutrino oscillations D) granulation E) nuclear fusion Charles Hakes Fort Lewis College 12 What evidence do we have for solar convection? A) sunspot polarity B) the Zeeman effect C) neutrino oscillations D) granulation E) nuclear fusion Charles Hakes Fort Lewis College 13 If Vega is apparent magnitude zero, and Deneb first magnitude, then A) Vega is about 100x brighter than Deneb.. B) Deneb is one magnitude brighter than Vega. C) Vega appears 2.5x brighter than Deneb. D) Deneb must be a main sequence star, and Vega a giant. E) Vega must be 2.5x more luminous than Deneb. Charles Hakes Fort Lewis College 14 If Vega is apparent magnitude zero, and Deneb first magnitude, then A) Vega is about 100x brighter than Deneb.. B) Deneb is one magnitude brighter than Vega. C) Vega appears 2.5x brighter than Deneb. D) Deneb must be a main sequence star, and Vega a giant. E) Vega must be 2.5x more luminous than Deneb. Charles Hakes Fort Lewis College 15 Luminosity • Luminosity - How much energy is coming from the star. • Solar constant (W/m2) measured above the Earth’s atmosphere. Charles Hakes Fort Lewis College 16 Figure 9.3 Solar Luminosity Solar Constant is the energy reaching the Earth above the atmosphere ~1400 W/m2 Charles Hakes Fort Lewis College 17 Luminosity • Luminosity - How much energy is coming from the star. • Solar constant (W/m2) measured above the Earth’s atmosphere. • Energy from the sun decreases as 1/r2 • Stars show same decrease with distance. Charles Hakes Fort Lewis College 18 Figure 10.4 Inverse-Square Law Charles Hakes Fort Lewis College 19 Figure 10.5 Luminosity • The more luminous, distant star appears the same brightness as the less luminous, closer star. Charles Hakes Fort Lewis College 20 Luminosity • Luminosity - How much energy is coming from the star. • Solar constant (W/m2) measured above the Earth’s atmosphere. • Energy from the sun decreases as 1/r2 • Stars show same decrease with distance. • For stars, instead of measuring in W/m2, use the “magnitude scale.” Charles Hakes Fort Lewis College 21 Small Group Exercise (Learning about the 1/r2 law.) • Get in groups of ~four people. • Assume each person has a superdeluxe flashlight left turned on by their front door. It is facing the classroom. • How much brighter does the closest flashlight look than the farthest flashlight? Charles Hakes Fort Lewis College 22 Figure P.12 Parallax Geometry Charles Hakes Fort Lewis College 23 Figure P.11 Parallax Recall information from the Prologue Charles Hakes Fort Lewis College 24 Figure 10.1 Stellar Parallax distance (pc) = Charles Hakes Fort Lewis College 25 1 parallax angle (arc sec) Distance Analogy • If the Sun is a marble… • The Earth is a grain of sand 1 m away. • The solar system is ~100 m in diameter Charles Hakes Fort Lewis College 26 Distance Analogy • If the Sun is a marble… • The Earth is a grain of sand 1 m away. • The solar system is ~100 m in diameter • The next star is in Albuquerque! Charles Hakes Fort Lewis College 27 Figure 10.2 Sun’s Neighborhood Charles Hakes Fort Lewis College 28 Parallax Measurements • Earth-based measurements can typically be made to 0.03”, or to a distance of ~30 parsecs (pc) • Distances to several thousand stars are known this way. • The Hipparcos satellite extends the distance to ~200 pc, so distances to nearly one million stars can be measured with parallax. Charles Hakes Fort Lewis College 29 Figure 10.3 Real Space Motion - Barnard’s Star 22 years apart • Nearby stars also show proper motion, or transverse velocities. • Only a few hundred show more than 1”/yr Charles Hakes Fort Lewis College 30 If a star has a parallax of 0.05”, then its distance must be A) 5 light years. B) 5 parsecs C) 20 light years. D) 20 parsecs. E) 200 parsecs Charles Hakes Fort Lewis College 31 If a star has a parallax of 0.05”, then its distance must be A) 5 light years. B) 5 parsecs C) 20 light years. D) 20 parsecs. E) 200 parsecs Charles Hakes Fort Lewis College 32 What peak wavelength is emitted in the core of the Sun (T=107K)? A) .29 cm B) .29 mm C) .29 nm D) .29 m E) .29 km Charles Hakes Fort Lewis College 33 What peak wavelength is emitted in the core of the Sun (T=107K)? A) .29 cm B) .29 mm C) .29 nm D) .29 m E) .29 km Charles Hakes Fort Lewis College 34 Compared to the 5800K photosphere, sunspots at 4500K emit what percent energy? A) 26% B) 36% C) 46% D) 56% E) 66% Charles Hakes Fort Lewis College 35 Compared to the 5800K photosphere, sunspots at 4500K emit what percent energy? A) 26% B) 36% C) 46% D) 56% E) 66% Charles Hakes Fort Lewis College 36 Three Minute Paper • Write 1-3 sentences. • What was the most important thing you learned today? • What questions do you still have about today’s topics? Charles Hakes Fort Lewis College 37