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TOPIC: The Sun


L

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RE: The Sun
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Eclipses Yield First Images of Elusive Iron Line in Solar Corona

Solar physicists attempting to unlock the mysteries of the solar corona have found another piece of the puzzle by observing the suns outer atmosphere during eclipses.
Ground-based observations reveal the first images of the solar corona in the near-infrared emission line of highly ionised iron, or Fe XI 789.2 nm. The observations were taken during total solar eclipses in 2006, 2008, and 2009 by astrophysicist Adrian Daw of NASAs Goddard Space Flight Center in Greenbelt, Md., with an international team of scientists led by Shadia Habbal from the University of Hawaiis Institute for Astronomy (IfA).

"The first image of the corona in Fe XI 789.2 nm was taken during the total solar eclipse of March 29, 2006" - Adrian Daw.

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Moreton wave
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Solar tsunami
Years ago, when solar physicists first witnessed a towering wave of hot plasma racing along the sun's surface, they doubted their senses. The scale of the thing was staggering. It rose up higher than Earth itself and rippled out from a central point in a circular pattern millions of kilometres in circumference. Skeptical observers suggested it might be a shadow of some kind - a trick of the eye - but surely not a real wave.

"Now we know. Solar tsunamis are real" - Joe Gurman of the Solar Physics Lab at the Goddard Space Flight Centre

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The prototype of a new solar patrol telescope in New Mexico recorded a tsunami-like shock wave rolling across the visible face of the Sun following a major flare even on Wednesday, Dec. 6, 2006, at 18:28 Universal Time (11:28 MST). The shock wave, known as a Moreton wave, also destroyed or compressed two filaments of cool gas at opposite sides of the solar hemisphere.
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Solar cycle 23
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Title: Periodicities in sunspot activity during solar cycle 23
Authors: Bhuwan Joshi, P. Pant, P. K. Manoharan

The data of sunspot numbers, sunspot areas and solar flare index during cycle 23 are analysed to investigate the intermediate-term periodicities. Power spectral analysis has been performed separately for the data of the whole disk, northern and southern hemispheres of the Sun. Several significant midrange periodicities (~175, 133, 113, 104, 84, 63 days) are detected in sunspot activity. Most of the periodicities in sunspot numbers generally agree with those of sunspot areas during the solar cycle 23. The study reveals that the periodic variations in the northern and southern hemispheres of the Sun show a kind of asymmetrical behaviour. Periodicities of ~175 days and ~133 days are highly significant in the sunspot data of northern hemisphere showing consistency with the findings of Lean (1990) during solar cycles 12-21. On the other hand, southern hemisphere shows a strong periodicity of about 85 days in terms of sunspot activity. The analysis of solar flare index data of the same time interval does not show any significant peak. The different periodic behaviour of sunspot and flare activity can be understood in the light of hypothesis proposed by Ballester et al. (2002), which suggests that during cycle 23, the periodic emergence of magnetic flux partly takes place away from developed sunspot groups and hence may not necessarily increase the magnetic complexity of sunspot groups that leads to the generation of flares.

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Solar Cycles 3 and 4
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Title: 155-day Periodicity in Solar Cycles 3 and 4
Authors: J. M. Vaquero, R. M. Trigo, M. Vazquez, M. C. Gallego

The near 155 days solar periodicity, so called Rieger periodicity, was first detected in solar flares data and later confirmed with other important solar indices. Unfortunately, a comprehensive analysis on the occurrence of this periodicity during previous centuries can be further complicated due to the poor quality of the sunspot number time-series. We try to detect the Rieger periodicity during the solar cycles 3 and 4 using information on aurorae observed at mid and low latitudes. We use two recently discovered aurora datasets, observed in the last quarter of the 18th century from UK and Spain. Besides simple histograms of time between consecutive events we analyse monthly series of number of aurorae observed using different spectral analysis (MTM and Wavelets). The histograms show the probable presence of Rieger periodicity during cycles 3 and 4. However different spectral analysis applied has only confirmed undoubtedly this hypothesis for solar cycle 3.

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RE: The Sun
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A lightning strike in Africa helps take the pulse of the sun
Tel Aviv University discovers an accurate tool for tracking solar rotation

Sunspots, which rotate around the sun's surface, tell us a great deal about our own planet. Scientists rely on them, for instance, to measure the sun's rotation or to prepare long-range forecasts of the Earth's health.
But there are some years, like this one, where it's not possible to see sunspots clearly. When we're at this "solar minimum," very few, if any, sunspots are visible from Earth. That poses a problem for scientists in a new scientific field called "Space Weather," which studies the interaction between the sun and the Earth's environment.
Thanks to a serendipitous discovery by Tel Aviv University's Prof. Colin Price, head of TAU's Department of Geophysics and Planetary Science, and his graduate student Yuval Reuveni, science now has a more definitive and reliable tool for measuring the sun's rotation when sunspots aren't visible - and even when they are. The research, published in the Journal of Geophysical Research - Space Physics, could have important implications for understanding the interactions between the sun and the Earth. Best of all, it's based on observations of common, garden-variety lightning strikes here on Earth.

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The Sun is the dimmest it has been for half a century but global temperatures have continued to rise. Are solar activity and the climate linked?
NASA data from the Solar and Heliospheric Observatory (SOHO) suggests that in 2008/9 the Sun was the dimmest it has been for over 50 years. The observed reduction in solar activity runs counter to solar researchers expectations that the suns activity should now be intensifying after a quiet period.

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Every 11 years, the sun undergoes a furious upheaval. Dark sunspots burst forth from beneath the sun's surface. Explosions as powerful as a billion atomic bombs spark intense flares of high-energy radiation. Clouds of gas big enough to swallow planets break away from the sun and billow into space. It's a flamboyant display of stellar power.
So why can't we see any of it?
Almost none of the drama of Solar Maximum is visible to the human eye. Look at the sun in the noontime sky and - ho-hum - it's the same old bland ball of bright light.

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Chromospheric Jet
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Title: An Intriguing Chromospheric Jet Observed by Hinode: I. Fine Structure Kinematics and Evidence of Unwinding Twists
Authors: Wei Liu, Thomas E. Berger, Alan M. Title, Theodore D. Tarbell

We report a chromospheric jet lasting for more than 1 hr observed by Hinode Solar Optical Telescope in unprecedented detail. The ejection occurred in three episodes separated by 12-14 min, with the amount and velocity of material decreasing with time. The upward velocities range from 438 to 33 km/s, while the downward velocities of the material falling back have smaller values (mean: -56 km/s) and a narrower distribution (standard deviation: 14 km/s). The average acceleration inferred from parabolic space-time tracks is 141 m/s, a fraction of the solar gravitational acceleration. The jet consists of fine threads (0.5-2.0 arcsec wide), which exhibit coherent, oscillatory transverse motions perpendicular to the jet axis and about a common equilibrium position. These motions propagate upward along the jet, with the maximum phase speed of 744 11 km/s at the leading front of the jet. The transverse oscillation velocities range from 151 to 31 km/s, amplitudes from 6.0 to 1.9 Mm, and periods from 250 to 545 s. The oscillations slow down with time and cease when the material starts to fall back. The falling material travels along almost straight lines in the original direction of ascent, showing no transverse motions. These observations are consistent with the scenario that the jet involves untwisting helical threads, which rotate about the axis of a single large cylinder and shed magnetic helicity into the upper atmosphere.

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RE: The Sun
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Satellite reveals surprising cosmic 'weather' at edge of solar system
The first solar system energetic particle maps show an unexpected landmark occurring at the outer edge of the solar wind bubble surrounding the solar system. Scientists will publish these maps, based mostly on data collected from NASA's Interstellar Boundary Explorer satellite, in the Oct. 15 issue of Science Express, the advance online version of the journal Science.


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NASA Spacecraft Provides First View of Our Place in the Galaxy
NASA's Interstellar Boundary Explorer, or IBEX, spacecraft has made it possible for scientists to construct the first comprehensive sky map of our solar system and its location in the Milky Way galaxy. The new view will change the way researchers view and study the interaction between our galaxy and sun.
The sky map was produced with data that two detectors on the spacecraft collected during six months of observations. The detectors measured and counted particles scientists refer to as energetic neutral atoms.


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-- Edited by Blobrana on Thursday 15th of October 2009 11:44:12 PM

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