Stars, Galaxies & the Universe Announcements HW#5 due Friday by 5 pm! Lab Observing Trip Thursday planning to go Meet outside VAN East end (Linn/Jefferson) Wear warm clothes! 1 Stars, Galaxies & the Universe Lecture Outline The Solar Exterior Granulation Sunspots Sunspots and the Sun s magnetic field Solar prominences Space Weather 2 Exterior Layers of the Sun: Photosphere: - visible surface of Sun - T = 5800 K - sunspots, surface features present Chromosphere: - just outside of photosphere - hot gas, magnetic features - T = 10,000 K Corona: - Very hot (few million degrees) - visible during eclipse, coronagraph 3 1
PHOTOSPHERE: visible surface of the Sun Two features: sharp edge limb brighter in center than along the limb limb darkening limb less dense less light emitted 4 Solar Surface: Granulation on the solar surface 1000 s miles across dark = cooler gas light = hotter gas speed of motion up & down measured by DOPPLER EFFECT! 5 Solar Granules: courtesy of the Swedish Solar Telescope 6 2
A side view of solar granules: 7 Photosphere: Sunspots Sunspot magnetic features on photosphere - cooler than photosphere (DARK) ~ 4000 K - many 10,000 km s across! Typical Sunspot activity major sunspot activity 8 Sunspot Cycle: Thenumber of sunspots changes daily The location of Sunspots changes daily 9 3
Sunspot Cycle: an 11-year cycle of sunspots The number of sunspots reaches a peak every 11 years data has been collected since ~1620! Maunder Minimum a period of cold (ice age) - records of mass starvation in Europe 10 Sunspot Cycle: Sunspot location also changes ~30 degrees of Sun s equator spots move gradually toward Sun s equator Butterfly Diagram 11 Sunspots are magnetic phenomena - they have a polarity direction (North or South) -they are thought to be the footpoints of magnetic fields which get tangled and ultimately ejected from surface filter image image showing N and S polarity 12 4
13 picture from the Swedish Solar Telescope 14 Sunspot Cycle: Can determine the rate of rotation of the Sun from the measurement of Sunspot Movement Galileo was first to attempt to measure Solar Rotation from his daily drawings of the sunspots 14 June 1613 12 July 1613 15 5
Solar Rotation varies between 25-35 days the Sun is not a solid body like a ball different parts rotate at different rates equator rotates very rapidly: 25 days poles take longer: 35 days 16 Sunspot Cycle: Sunspot polarity also changes every ~11 years North and South polarity reverse total Solar Cycle is 22 years ultimately linked to the Sun s magnetic field 17 18 6
19 Sunspots likely to be magnetic in nature but what s the proof? 20 How do we know phenomena on the Sun (sunspots, flares) are magnetic in nature? The Zeeman Effect When in a strong magnetic field (such as an active region on the sun), a spectral line splits into 2 or more components. Why? The presence of a magnetic field actually produces different energy levels allowing different transitions between the levels to occur. Stronger magnetic fields produce more splitting. Splitting 29 Sept 2010 α B SGU - Dr. C. C. Lang 21 7
What a spectral line will do in the presence of a magnetic field the central peak will split into three peaks of lower strength no magnetic field in presence of magnetic field What this looks like in real data in region where sunspot is, lines are split; otherwise they are not 22 23 Prominences and Flares rooted in sunspots and rise into Coronal regions 24 8
25 Chromosphere: a tenuous region that lies right above Sun s surface so little material, we can see right through it SPICULES Jets of gas shooting up from surface shortlived: 5 mins. ~100,000 spicules on the Sun s surface often appears in red visible light 26 Chromosphere red light at λ=656.3 nm glowing hydrogen 27 9
Solar Prominence: an eruption on Sun s surface 28 29 30 10
31 Corona: million degree halo surrounding Sun 32 Solar Flares: Larger eruption in Corona usually due to changes in the Sun s magnetic field organization 29 Sept 2010 SGU - twisting - Dr. C. C. and Lang turning with rotation 33 11
Prominences and Flares rooted in sunspots and rise into Coronal regions 34 Huge range of temperatures outside of Sun s surface 1. Photosphere 5700 K 2. Chromosphere ~ 10,000 000 K 3. Corona ~ 1 million K Unsolved mystery: How does the Corona get so hot?? 35 Coronal Mass Ejection Blast of gas/particles moving out from the Corona Speeds as high as 1000 km/s 50,000 km above the Sun s surface 36 12
Recent Coronal Mass Ejection: 5 Sept 2005 37 Solar Wind: a not very dense flow of particles from Solar Corona into space moves past Earth ~4 days after it leaves Sun 38 Van Allen Belts protect Earth from highly-charged (energetic) Solar particles! - discovered by Dr. James Van Allen in 1958 - first flight of a U.S. Earth-orbiting satellite -Van Allen insisted that Geiger counter be on board to count particle detections (found VA Belts!!) 39 13
October 4th 1957-50th anniversary - first artificial satellite orbits the Earth! IGY - International Geophysical Year (July 1957-December 1958) The US program included investigations of aurora and airglow, cosmic rays, geomagnetism, glaciology, gravity, the ionosphere, determinations of longitude and latitude, meteorology, oceanography, seismology, solar activity, and the upper atmosphere. The world's first artificial i satellite - size of a beach ball (22.8 inches diameter) - weighed 83.6 kg (183.9 lbs) (US effort ~4 lbs) - took 98 minutes to orbit the Earth, h=900 km Changed way people thought about the world -fear of on-board nuclear weapons - increased US space effort - November 3rd, 1957 Sputnik 2 launched with first on-board passenger (Laika, a dog!) Sputnik - Sputnik 2 was ~1000 lbs, orbited for 200 days! 40 Sputnik 41 January 31st 1958: Launch of Explorer 1 After Sputnik, US effort was increased - charge was to get an artificial satellite up! 84 days later, Explorer 1 launched - scientific instruments built by Dr. Van Allen, rest designed by Pickering Explorer-I was placed in an orbit with a perigee of 224 miles and an apogee of 1,575 miles having a period of 114.9 minutes. Weight was 30.66 lbs (18.35 lbs instrumentation) Instrumentation built to detect cosmic rays -highly-energetic charged particles (90% protons, 9% alpha particles & 1% electrons) - where do they come from? Once in orbit, Explorer 1 detected fewer cosmic rays Than predicted -Van Allen s theory that there Were belts trapping the Sputnik 29 Sept 2010 Cosmic SGU rays -in Dr. them C. C. Lang 42 14
Van Allen s Early Experiments: Rockoons Rockoon - hybrid instrument: Rocket and balloon The rockoon was a solid fuel rocket that, rather than being immediately lit while on the ground, was first carried into the upper atmosphere a gas-filled balloon, and then separated from the balloon when it had reached its maximum height and automatically ignited. As TIME reported in 1959, Van Allen s Rockoons could not be fired in Iowa for fear that the spent rockets would strike an Iowan or his house. So Van Allen convinced the U.S. Coast Guard to let him fire his rockoons from the icebreaker Eastwind that was bound for Greenland. The first balloon rose properly to 70,000 ft., but the rocket hanging under it did not fire. The second Rockoon behaved in the same maddening way. On the theory that extreme cold at high altitude might have stopped the clockwork supposed to ignite the rockets, Van Allen heated cans of orange juice, snuggled them into the third Rockoon s gondola, and wrapped the whole business in insulation. The rocket fired. Sputnik 43 Auroral Phenomena Sometimes magnetosphere gets overloaded with charged particles Solar wind electrons precipitate into polar regions, ionizing nitrogen and oxygen 44 atoms 45 15
University of Iowa Space Physics Research group led by Dr. Craig Kletzing in U Iowa s Physics & Astronomy Dept. study of particles in auroral regions, magnetic fields, energetics of this region build/design detectors and instruments here in Van Allen Hall launch the spacecraft into the auroral regions from northern Alaska at night 46 47 16