* Astronomy

Blobrana · L

RE: The Sun

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Scientists may have found a new tool to trace the Sun's journey through our galaxy, the Milky Way.

It takes the Sun and its family of planets about 220 million years to complete each orbit of the galaxy, but it can be quite difficult to detect the local interstellar medium, which the solar system's travelling through, because it's so tenuous and emits very little light.
Priscilla Frisch from the University of Chicago and Hans-Reinhard Mueller from Dartmouth College in Hanover, believe changes in the isotopes of some elements in Earth's geologic record could hold clues about this journey.
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Is dark matter cooling off Sun's core?

Dark matter is cooling off the core of our sun, according to two research groups.
While the insight doesn't significantly affect the sun's overall temperature, a cool core would shed new light on the way heat is distributed and transported within the sun.
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Scientists find a big drop in the strength of solar magnetic fields

Although sunspots are making a belated comeback after the protracted solar minimum, the signs are that all is not well. For decades, William Livingston at the National Solar Observatory in Tucson has been measuring the strength of the magnetic fields that puncture the sun's surface and cause the spots to develop.Read more

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For the first time, astronomers have found that the magnetic field in the outer atmosphere of the Sun produces eerie musical harmonies -- a discovery that could provide new ways of understanding and predicting solar flares before they happen.
Scientists at the University of Sheffield found that huge magnetic loops that have been observed coiling away from the outer layer of the Sun's atmosphere -- known as coronal loops -- vibrate like strings on a musical instrument.
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What's wrong with the sun?

Sunspots come and go, but recently they have mostly gone. For centuries, astronomers have recorded when these dark blemishes on the solar surface emerge, only for them to fade away again after a few days, weeks or months. Thanks to their efforts, we know that sunspot numbers ebb and flow in cycles lasting about 11 years.
But for the past two years, the sunspots have mostly been missing. Their absence, the most prolonged for nearly a hundred years, has taken even seasoned sun watchers by surprise.
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What's wrong with the sun?

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Title: Are Uranus & Neptune responsible for Solar Grand Minima and Solar Cycle Modulation?
Authors: Geoff Sharp
(Version v2)

Detailed solar Angular Momentum (AM) graphs produced from the Jet Propulsion Laboratory (JPL) DE405 ephemeris display cyclic perturbations that show a very strong correlation with prior solar activity slowdowns. These same AM perturbations also occur simultaneously with known solar path changes about the Solar System Barycentre (SSB). The AM perturbations can be measured and quantified allowing analysis of past solar cycle modulations along with the 11,500 year solar proxy records (14C & 10Be). The detailed AM information also displays a recurring wave of modulation that aligns very closely with the observed sunspot record since 1650. The AM perturbation and modulation is a direct product of the outer gas giants (Uranus & Neptune). This information gives the opportunity to predict future grand minima along with normal solar cycle strength with some confidence. A proposed mechanical link between solar activity and planetary influence via a discrepancy found in solar/planet AM along with current AM perturbations indicate solar cycle 24 & 25 will be heavily reduced in sunspot activity resembling a similar pattern to solar cycles 5 & 6 during the Dalton Minimum (1790-1830).

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Title: Astrometric jitter of the sun as a star
Authors: V.V. Makarov, D. Parker, R.K. Ulrich
(Version v2)

The daily variation of the solar photocenter over some 11 years is derived from the Mount Wilson data reprocessed by Ulrich et al. 2010 to closely match the surface distribution of solar irradiance. The standard deviations of astrometric jitter are 0.52 \mu AU and 0.39 \mu AU in the equatorial and the axial dimensions, respectively. The overall dispersion is strongly correlated with the solar cycle, reaching 0.91 \mu AU at the maximum activity in 2000. The largest short-term deviations from the running average (up to 2.6 \mu AU) occur when a group of large spots happen to lie on one side with respect to the centre of the disk. The amplitude spectrum of the photocenter variations never exceeds 0.033 \mu AU for the range of periods 0.6--1.4 yr, corresponding to the orbital periods of planets in the habitable zone. Astrometric detection of Earth-like planets around stars as quiet as the Sun is not affected by star spot noise, but the prospects for more active stars may be limited to giant planets.

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Title: Is the Polar Region Different from the Quiet Region of the Sun?
Authors: Hiroaki Ito, Saku Tsuneta, Daikou Shiota, Munetoshi Tokumaru, Ken'ichi Fujiki

Observations of the polar region of the Sun are critically important for understanding the solar dynamo and the acceleration of solar wind. We carried out precise magnetic observations on both the North polar region and the quiet Sun at the East limb with the Spectro-Polarimeter of the Solar Optical Telescope aboard Hinode to characterise the polar region with respect to the quiet Sun. The average area and the total magnetic flux of the kG magnetic concentrations in the polar region appear to be larger than those of the quiet Sun. The magnetic field vectors classified as vertical in the quiet Sun have symmetric histograms around zero in the strengths, showing balanced positive and negative flux, while the histogram in the North polar region is clearly asymmetric, showing a predominance of the negative polarity. The total magnetic flux of the polar region is larger than that of the quiet Sun. In contrast, the histogram of the horizontal magnetic fields is exactly the same between the polar region and the quiet Sun. This is consistent with the idea that a local dynamo process is responsible for the horizontal magnetic fields. A high-resolution potential field extrapolation shows that the majority of magnetic field lines from the kG-patches in the polar region are open with a fanning-out structure very low in the atmosphere, while in the quiet Sun, almost all the field lines are closed.

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Sun's constant size surprises scientists

A group of astronomers led by the University of Hawaii's Dr. Jeff Kuhn has found that in recent times the sun's size has been remarkably constant. Its diameter has changed by less than one part in a million over the last 12 years.
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