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The Sun (part 2): The Varying Sun and its Effect on Earth

The Sun (part 2): The Varying Sun and its Effect on Earth. Announcements. Final exam – Tuesday, May 8, 8-10AM (308 Kuiper) Brief review today Practice final exam is now posted on the course website Pick up past assignments! Solutions to last HW will be posted on the course website soon

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The Sun (part 2): The Varying Sun and its Effect on Earth

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  1. The Sun (part 2):The Varying Sun and its Effect on Earth

  2. Announcements • Final exam – Tuesday, May 8, 8-10AM (308 Kuiper) • Brief review today • Practice final exam is now posted on the course website • Pick up past assignments! • Solutions to last HW will be posted on the course website soon • Office Hours as usual

  3. The Sun varies with an 11-year cycle called “the solar cycle” • Currently, we are near the minimum in the solar cycle Number of Sunspots versus time – they come and go every 11 years

  4. These variations result from the way magnetic fields are generated within the interior of the Sun: The Solar Dynamo

  5. The number of sunspots at the peak in the 11-year cycle is variable • The Maunder Minimum was a period from 1645-1715 in which very few sunspots were recorded • About 50 during this period compared to ~50,000 over a similar time interval in the 1900’s • During the Maunder minimum, there was a period of extremely cold winters in northern Europe • The “Little Ice Age” • Other cycles and climatic changes have been recorded using proxy records (tree rings, ice cores, riverbed sediments)

  6. The River Thames (in London) froze over during a period within the “Little Ice Age” as depicted in this painting by Abraham Hondius

  7. The Sun’s role in Global Warming • The Sun is more active in recent cycles, than in the past • This increased activity contributes to warming the Earth • However, the largest contributor to global warming is the increase in man-made green house gases

  8. The Sun is slightly dimmerduring sunspot minimum as seen by recent, highly sensitive (but not inter-calibrated!) measurements Solar Energy arriving at Earth’s orbit “The Solar Constant” ↑ ↑ Sunspot Minimum Sunspot Minimum

  9. Effects of Geomagnetic Storms on Earth • disrupted communication • Radio signals, telegraph wires, cell phones • Overloaded power grids (induced ground currents) • Oil pipeline corrosion (induced ground currents) • Dangerous intensities of energetic particles and space radiation • Extended atmosphere that can cause drag on low-orbiting spacecraft • Confused homing pigeons, sperm-whale strandings, mammal population cycles? NOAA has a list of “severity scales” on their website http://www.sec.noaa.gov/NOAAscales/index.html#GeomagneticStorms

  10. Aurora in Tucson (March, 2001) Over-exposed moon ↓

  11. The Space Radiation and Particle Environment Solar Photons (x-rays, UV) Trapped particles (atomic nuclei) Solar-Energetic Particles (atomic nuclei) Cosmic Rays (atomic nuclei) Cosmic-rays (mostly protons) originate from supernovae explosions. They move at very nearly the speed of light

  12. Galactic Cosmic Rays and the Solar Cycle

  13. Cosmic rays are dangerous to unprotected life • When a cosmic ray strikes skin, it can damage DNA and may cause cancer • The precise effect of cosmic rays on humans (cosmic-ray intensity vs. radiation dosage, how rapidly DNA can repair itself, etc.) is under study.

  14. Our natural shields • Heliosphere • is a barrier to low-energy galactic cosmic rays Atmosphere shields nearly all cosmic rays, x-rays, some UV • Earth’s Magnetic field • shields most solar particles, and low-energy cosmic rays • worse in polar regions and South Atlantic Anomaly (SAA)

  15. NASA limits on human radiation exposure are designed to lead to a <3% increase in lifetime fatal cancer risk and to ensure that astronauts do not suffer short-term radiation effects • Dose Equivalent is measured in units of Sieverts (or REM).     • 1 Sv = 100 REM • 0.01 REM per routine chest x-ray image • 4 REM for a CAT scan • BFO = Blood-forming organs 20,000 chest x-rays 10,000 chest x-rays

  16. The solar minimum intensity of Galactic cosmic rays (GCRs) is enough to exceed the current radiation limits for astronauts in low Earth orbit (rem) Dose Eq. (rem) Mewaldt et al. 2006

  17. But – new data indicate that another big threat is from solar-energetic particles (SEPs). This plot shows how much SEPs vary from one “event” to the next (the one with the dark green arrow is a 1 million –fold increase in the intensity) ↓ Solar Energetic Particles (SEPs) Galactic cosmic rays (GCRs)

  18. Shielding from Huge Solar Particle Events ← This as an enormous solar superstorm that occurred in 1859 DOSE (GY) Based on Wilson (1997), Townsend (2003), Kim et al. (2005), and Turner (2006)

  19. Fortuitous timing of Apollo missions

  20. What would happen during a big event such as that which occurred in Aug. 1972 (between Apollo 16 and 17)? • It takes about 20 minutes for the earliest arriving particles to reach Earth • It takes about 8 minutes for light to travel to Earth, which would be the earliest warning sign • It will take at least 5-10 minutes to decide what to do • This leaves very little time to actually do something A huge (X28) flare that occurred during the “Halloween” solar storms period

  21. So when would be the best time to send humans on a > 30-month trip to Mars? • Solar Maximum might be the best option • Galactic cosmic rays are reduced • Solar-energetic particles are increased significantly, but we may be able to shield astronauts from these. • Solar Minimum is probably a bit riskier • More galactic cosmic rays • Huge solar flares can occur, even during solar minimum

  22. To Finish Producer of breathtaking Arizona sunsets; but a powerful, feisty and unpredictable neighbor ↓

  23. Final Exam • Format: • ~ 5 short answer questions • ~ 35 multiple choice questions • Closed book, closed note, no electronic devices (including a calculator!) • You will have 2 full hours to take the exam • What will it cover? • 75% of the exam will be from material since last exam • Chapters 12-15, parts of 16 (see last lecture) • 25% from topics covered throughout the course • A brief review of these follows Extraterrestrial Life 5/6/08

  24. Final Exam • What should you study? • Go over lecture slides • Go over questions at the beginning of each chapter • Go over key ideas and review questions at the end of each chapter • Go over in-class activities, quizzes, and homework (except for mathematical questions) • The solutions are on the website A practice exam is now posted on the website

  25. Final Exam: A brief review of comprehensive material (25% of exam) • Chapters 1,2,4 : Basic Astronomy • The motion and position of objects in the sky • Diurnal motion, direct and retrograde motion of the planets • Kepler’s laws • gravity • Chapter 5: Spectroscopy and the nature of light • Wien’s Law, Stefan-Boltzman law • The Electromagnetic Spectrum • Emission and absorption lines in spectra

  26. Final Exam: A brief review of comprehensive material (25% of exam) • Chapters 7 and 8: The layout, nature, origin, age, and formation of the Solar System • Basic solar-system properties • Terrestrial planets and gas giants • All planets orbit the Sun in the same direction and in the same plane • Density of the planets • The Solar Nebula • The nebular hypothesis of the formation of the solar system

  27. Final Exam: A brief review of comprehensive material (25% of exam) • Basic Planetary processes • Interiors and Surfaces • Impact cratering • Planetary Magnetic Fields • Atmospheres • Chapter 9: The Earth • Plate tectonics • Structure of the interior • Atmosphere and greenhouse effect Extraterrestrial Life 5/6/08

  28. Final Exam: A brief review of comprehensive material (25% of exam) • Chapters 10 and 11: The Moon and Mercury • Lots of craters – why? • Basic surface geology (highlands, mare) • No atmosphere – why ? • Synchronous rotation (due to tidal forces) • Chapter 11: Venus • Why does it exhibit phases ? And why is it so bright? • Runaway greenhouse effect • Chapter 11: Mars • Why is it at opposition every 2 years (nearly) ? • What is the evidence for Water • Atmosphere (thin, mostly CO2, runaway “icehouse” effect) • Basic geology (lots of craters, north/south crustal dichotomy)

  29. Final Exam: A brief review of Chapters 12-16 (75% of exam) • Chapters 12 : Jupiter and Saturn • Orbits • composition • Rotation (Jupiter rotates the most rapidly) • How do we know the rotation rate? • Oblateness (Saturn is the most oblate) • Features of the upper atmosphere • Belts, and Zones, Giant Red Spot (Jupiter) • Interiors • Magnetic Fields • Jupiter – extremely strong • Saturn – aligned with rotation axis • Planetary Rings (formation, gaps, which planets have them? Saturn’s rings, etc.) Extraterrestrial Life 5/6/08

  30. Final Exam: A brief review of Chapters 12-16 (75% of exam) • Chapter 13: Jupiter and Saturn’s Moons • Galilean Satellites: A Solar system in miniature • Properties of Io, Europa, Ganymede, and Callisto • What is the Io torus? • Titan and Enceladus • Tidal forces • tidal heating of the moons • Roche limit

  31. Final Exam: A brief review of Chapters 12-16 (75% of exam) • Chapter 14: The Outer Worlds • Uranus and Neptune • How were they discovered? • Interior and Atmosphere • Why are they blue-green in color? • Uranus has an unusual tilt • Both have unusual magnetic fields • Pluto and Kuiper Belt Objects • Discovery • Charon • General characteristics of these objects

  32. Final Exam: A brief review of Chapters 12-16 (75% of exam) • Chapter 15: Asteroids/Comets/Meteorites • Asteroid Belt, Kuiper Belt, Oort Cloud • Kirkwood Gaps • Trojan Asteroids • Asteroids physical properties • “Rubble piles” • Meteorites • Stony, irons, stony-irons, carbonaceous chondrites • Comets • Basic structure • Orbits • Meteor showers • Chapter 16 (parts of it): The Sun – the last two lectures

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