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Astronomers surprised by Sun's constant size

The Sun's size has been remarkably constant in recent times - a finding that has taken astronomers by surprise as our nearest star's diameter has changed by less than one part in a million over the last 12 years.
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First Light for the Solar Dynamics Observatory

At a press conference today in Washington DC, researchers unveiled "First Light" images from NASA's Solar Dynamics Observatory, a space telescope designed to study the sun.
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Low solar activity link to cold UK winters

The UK and continental Europe could be gripped by more frequent cold winters in the future as a result of low solar activity, say researchers.
They identified a link between fewer sunspots and atmospheric conditions that "block" warm, westerly winds reaching Europe during winter months.

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Magnetic 'ropes' tie down solar eruptions

Over the last century, astronomers have become very aware of how just dynamic the Sun really is. One of the most dramatic manifestations of this is a coronal mass ejection (CME) where billions of tons of matter is thrown into space. If a CME reaches the Earth it creates inclement 'space weather' that can disrupt communications, power grids and the delicate systems on orbiting satellites. This potential damage means there is a keen interest in understanding exactly what triggers a CME outburst.
Now a team of researchers from University College London (UCL) have used data from the Hinode spacecraft, revealing new details of the formation of an immense magnetic structure that erupted to produce a CME on the 7th December 2007. Lead researcher Dr Lucie Green will present their results on Monday 12th April at the RAS National Astronomy Meeting in Glasgow.
The Sun's behaviour is shaped by the presence of magnetic fields that thread through the solar atmosphere. The magnetic fields may take on different shapes from uniform arches to coherent bundles of field lines known as 'flux ropes'. Understanding the exact structure of magnetic fields is a crucial part of the effort to determine how the fields evolve and the role they play in solar eruptions. In particular, flux ropes are thought to play a vital role in the CME process, having been frequently detected in interplanetary space as CMEs reach the vicinity of the Earth.

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Solar 'Current of Fire' Speeds Up

NASA solar physicist David Hathaway reports that the top of the sun's Great Conveyor Belt has been running at record-high speeds for the past five years.
The Great Conveyor Belt is a massive circulating current of fire (hot plasma) within the sun. It has two branches, north and south, each taking about 40 years to complete one circuit. Researchers believe the turning of the belt controls the sunspot cycle.

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During the recent solar activity minimum, the Sun was the dimmest X-ray star within 23 light years of its neighbourhood - this is suggested by measurements collected by scientists at the Space Research Centre (SRC) of the Polish Academy of Sciences.
The measurements were made using the Polish-built super-sensitive instrument SphinX located aboard the solar orbiting observatory CORONAS-Photon.

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NOAA Scientist Finds Clue to Predicting Solar Flares

For decades, experts have searched for signs in the sun that could lead to more accurate forecasts of solar flares - powerful blasts of energy that can supercharge Earth's upper atmosphere and disrupt satellites and the land-based technologies on which modern societies depend.
Now a scientist at NOAA's Space Weather Prediction Centre and her colleagues have found a technique for predicting solar flares two to three days in advance with unprecedented accuracy.

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Sun's long slumber a wake-up call to solar scientists

The sun once was considered a steady star without change. The sun's energy output, as measured above the earth's atmosphere, was called "the solar constant." As astronomers studied the sun, they realized that this notion wasn't quite correct. They found that the solar output varied slightly by a few tenths of a percent. The amount rose when the sun was active (solar maximum) and declined when it was quiet (solar minimum).
Solar astronomers counted the number of dark spots on the disk of the sun to gauge the sun's activity. In 1843, a German amateur astronomer, Samuel H. Schwabe, realised that the number of sunspots varied over time. The average cycle goes from a few to many spots and back in about 11 years. A few years later, Rudolph Wolf, a Swiss astronomer, confirmed the roughly 11-year cycle. He numbered the sun spot cycles beginning in 1755 as Cycle Number One. In 1852, four astronomers realised that the activity of the sun and the geomagnetic activity on earth were interrelated. That was the beginning of the sun-earth connection and space weather.

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Solar System
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Title: Orbital effects of Sun's mass loss and the Earth's fate
Authors: Lorenzo Iorio
(Version v2)

I calculate the classical effects induced by an isotropic mass loss of a body on the orbital motion of a test particle around it. By applying my results to the phase in which the radius of the Sun, already moved to the Red Giant Branch of the Hertzsprung-Russell Diagram, will become as large as 1.20 AU in about 1 Myr, I find that the Earth's perihelion position on the fixed line of the apsides will increase by about 0.22-0.25 AU (for \dot M/M = 2 x 10^-7 yr^-1); other researchers point towards an increase of 0.37-0.63 AU. Mercury will be destroyed already at the end of the Main Sequence, while Venus should be engulfed in the initial phase of the Red Giant Branch phase; the orbits of the outer planets will increase by 1.2-7.5 AU. Simultaneous long-term numerical integrations of the equations of motion of all the major bodies of the solar system, with the inclusion of a mass-loss term in the dynamical force models as well, are required to check if the mutual N-body interactions may substantially change the picture analytically outlined here, especially in the Red Giant Branch phase in which Mercury and Venus may be removed from the integration.

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The sun may finally be awakening from its longest quiet period in about a century and powering up to solar maximum, when it could fling disruptive electromagnetic storms toward Earth.
But once the sun does ramp up, it could be a relatively quiet solar maximum, with a below-average number of eruptions, scientists say.
Some researchers argue the sun has begun to enter solar maximum; others say it's not there yet. They do agree the current quiet period, or solar minimum, is the longest since the early 1900s, but they don't know why.

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