* Astronomy

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RE: The Sun

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Heliosphere

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RE: The Sun

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Could the Sun's inactivity save us from global warming? David Whitehouse explains why solar disempower may be the key to combating climate change
Something is happening to our Sun. It has to do with sunspots, or rather the activity cycle their coming and going signifies. After a period of exceptionally high activity in the 20th century, our Sun has suddenly gone exceptionally quiet. Months have passed with no spots visible on its disc. We are at the end of one cycle of activity and astronomers are waiting for the sunspots to return and mark the start of the next, the so-called cycle 24. They have been waiting for a while now with no sign it's on its way any time soon.

Seasons of the Sun

Modern Solar Minimum
(2000-?)

Modern Climate Optimum
(18902000) the world is getting warmer. Concentrations of greenhouse gas increase. Solar activity increases.

Dalton Solar Minimum
(17901820) global temperatures are lower than average.

Maunder Solar Minimum
(16451715) coincident with the 'Little Ice Age'.

Spörer Solar Minimum
(1420-1530) discovered by the analysis of radioactive carbon in tree rings that correlate with solar activity colder weather. Greenland settlements abandoned.

Wolf Solar Minimum
(12801340) climate deterioration begins. Life gets harder in Greenland.

Medieval Solar Maximum
(10751240) coincides with Medieval Warm Period. Vikings from Norway and Iceland found settlements in Greenland and North America.

Oort Solar Minimum
(1010-1050) temperature on Earth is colder than average.

There seem to have been 18 sunspot minima periods in the last 8,000 years; studies indicate that the Sun currently spends up to a quarter of its time in these minima.

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HI-RES JPG
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This is a composite of several images taken by the Extreme ultraviolet Imaging Telescope (EIT) on board SOHO, taken at a wavelength of 17.1 nanometres, shown in blue. It shows plasma at a temperature of about 1 million Kelvin. The images were shot over an entire solar cycle and illustrate the changes in solar activity.

Credits: SOHO/EIT (ESA & NASA)

The Solar and Heliospheric Observatory (SOHO) celebrated its twelfth launch anniversary on 2 December 2007. The satellite has witnessed the Sun change through almost a complete solar cycle - from quiet to stormy, and back again.
The solar cycle normally lasts about 11 years. In late 1996, shortly after its launch, SOHO was able to observe the last minimum of the 11-year activity cycle. The minimum was followed by a rapid rise in solar activity, peaking 2001 and 2002.

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The Sun may be smaller than we thought, a new study argues.
If correct, then other properties of the Sun such as its internal temperature and density may be slightly different than previously calculated. Understanding the Sun's interior is important as it might help scientists make predictions about space weather and answer questions about the solar system.
The Sun has no solid surface. Its atmosphere merely gets thinner and more transparent farther from its centre.
Instead the Sun's "surface" is defined to be the depth in the Sun's atmosphere where it becomes opaque to light. Scientists measure this by observing the Sun with telescopes and measuring the distance between the centre of the Sun's disc and its "edge" the place where its brightness suddenly drops off. This gives a radius of 695,990 kilometres, or about 109 times the radius of Earth.
A second, completely different way to measure the Sun's size is by using surface gravity waves called f-modes that ripple across the surface of the Sun like water waves on the ocean.

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Astronomy Sunspots
We live in the extended atmosphere of our indispensably dynamic sun that provides us with energy vital for our existence on earth. Although it is considered an ordinary star, its radiant energy is produced uniquely by complex thermonuclear transmutation of hydrogen into helium at an unimaginable temperature of about 16 million Kelvin in its centre (zero degrees Kelvin is equivalent to minus 273 degrees Centigrade). Some 4.26 million tons of matter are converted into energy, releasing 383 yotta watts (10 to the power 26) every second primarily in the form of heat and light, of which one tiny portion arrives on our blue planet.

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As reservoirs of valuable information go, nothing beats the sun. This sphere of heat and energy holds 99.9 percent of the solar system, saved in all original proportions after planets and meteorites formed. Analysing the mix of hydrogen, oxygen and noble gases found in the sun can answer one of the biggest questions of the universe: How did our solar system evolve?

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Sol

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Title: A Tale Of Two Spicules: The Impact of Spicules on the Magnetic Chromosphere
Authors: Bart De Pontieu, Scott W. McIntosh, Viggo H. Hansteen, Mats Carlsson, C.J. Schrijver, T.D. Tarbell, A.M. Title, R.A. Shine, Y. Suematsu, S. Tsuneta, Y. Katsukawa, K. Ichimoto, T. Shimizu, S. Nagata
(Version v2)

We use high-resolution observations of the Sun in Ca II H 3968 A from the Solar Optical Telescope on Hinode to show that there are at least two types of spicules that dominate the structure of the magnetic solar chromosphere. Both types are tied to the relentless magnetoconvective driving in the photosphere, but have very different dynamic properties. "Type-I" spicules are driven by shock waves that form when global oscillations and convective flows leak into the upper atmosphere along magnetic field lines on 3-7 minute timescales. "Type-II" spicules are much more dynamic: they form rapidly (in ~10s), are very thin (<200km wide), have lifetimes of 10-150s (at any one height) and seem to be rapidly heated to (at least) transition region temperatures, sending material through the chromosphere at speeds of order 50-150 km/s. The properties of Type II spicules suggest a formation process that is a consequence of magnetic reconnection, typically in the vicinity of magnetic flux concentrations in plage and network. Both types of spicules are observed to carry Alfven waves with significant amplitudes of order 20 km/s.

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