The solar wind is a gas plasma blown off the surface of our sun at a million miles per hour. It is the outer atmosphere of the sun expanding out into space in all directions all the time. It effectively forms a shield around our solar system like a bubble that is called the heliosphere that tends to reflect harmful cosmic rays originating from other star systems, basically pushing away the rest of the galaxy from our solar system. This outward flow of particles is constant and creates outbound pressure referred to as a wind, a solar wind.

Sometimes it is stronger than at other times. Apparently, it is also sometimes weaker, as new data suggest.

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An image of the sun taken Sept 25 using the SOHO observatory’s Extreme ultraviolet Imaging Telescope at 304 Angstrom. SOHO, NASA/ESA

This is perplexing. The strength of the wind forms a pressure barrier that repels the intergalactic cosmic radiation, which is quite harmful to life, especially life floating around in space, space stations and spacecraft. Earth is protected by its magnetosphere and by its atmosphere for two additional tiers of protection. Spacecraft orbiting the Earth would also be protected by its magnetosphere. Spacecraft en route to the moon would have minimal protection.

The spacecraft Ulysses launched in October 1990, is a mission out of the plane of the planets orbiting the polar regions of the sun. Ulysses has detected a gradual decrease in the solar wind over the last 15 years equal to nearly 25%.

A segment today on Science Friday, talks to David McComas, Principal Investigator for Solar Wind Observations over the Poles of the Sun (SWOOPS) Experiment, about the solar wind and the findings by the spacecraft Ulysses. The archived podcast should be available later today here.

The Ulyssess/SWOOPS web site is here: http://swoops.lanl.gov/ .

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The outermost layer of the sun is constantly active with turbulence; creating pressure waves or quakes that ripple the surface of the sun; seemingly making the sun “breathe” by heaving the surface up and down in a pattern of peaks and troughs.

The Solar Heliospheric Observatory (SOHO) has provided data recently showing these quakes that follow the wake of solar flares exploding above the surface of the sun.

The SOHO spacecraft shows scientists how the ripples move around the sun and provides information about the interior of the sun, helping us to understand what goes on there.

There is an unusual regularity to the “breathing” which is a class of vibrations, or oscillations, call the five-minute oscillations. Using SOHO to study these oscillations, scientists have discovered an unexpected correlation with solar flares, particularly the number of flares occurring.

Apparently as the number of flares increase, so does the strength of these five-minute oscillations. In other words, it seems the sun essentially “breathes” deeper and heavier with more solar flares occurring. Similarly on Earth after large earthquakes, the Earth vibrates with seismic waves. It is as if someone hit a church bell and after the loud initial ring, you would still hear the fading sound of the bell’s vibrations as it slowly stills quiet.

The image above was taken by the SOHO spacecraft on November 4, 2003. Shown is hot gas in the solar atmosphere in false color; the flare is the bright, white area on the right edge of the sun. The horizontal line showing through the flare is not real but a condition of the instrument’s detector becoming over saturated from the intense light.

 

 

An large solar eruption occurred on the Sun on April 9, 2008. This prominence was captured by the STEREO Ahead spacecraft showing the prominence as it twisted just above the surface of the Sun. The event was also captured by the STEREO Behind spacecraft, Hinode, TRACE and SOHO missions.

I am fascinated by Solar ejectionpictures of the Sun and the various events that occur on it. In a larger view of this picture, which can be found by clicking on the SOHO missions link above, the prominence looks to me like a large jellyfish with its tentacles falling down below it as it lifts itself above the Sun with the tentacles falling below  and touching the Sun.

The Sun is constantly emitting material out into space, sometimes with more bulk than other times, and it is these emissions than can pose a danger to astronauts in space as well as to Earth itself.

Were it not for the magnetic fields surrounding Earth that serve to deflect most of the emissions and radiation from the Sun, Earth would be sterile with no possibility for life forming. Scientists are currently putting a lot of resources into studying the Sun, its cycles and behavior. Solar flares often affect communication satellites, so attempts to predict these solar events are a prime objective of the missions.

The spacecraft Ulysses is flying over the Sun’s north pole just as a new solar sun cycle is beginning. The flyby began November 2007 and will continue through March 2008. Ulysses was launched in October 1990 from the space shuttle Discovery. Previous flybys of the Sun’s poles occurred in 1994-95, 2000-01 and 2007.

Solar wind speed vs latitude When sunspots break up, their magnetic fields decay and get carried towards the poles by action of vasts seas of plasma, making the poles a “graveyard for sunspots”. The older magnetic fields fall under the polar surface down to the sun’s inner magnetic dynamo, about 124,000 miles down (200,000km). Once there, the solar dynamo action amplifies the magnetic fields which again become used in future solar cycles, a sort of recycling effect.

On previous flybys of the solar poles, the magnetic north pole during the previous solar cycle was 8% cooler than the south pole, or about 80,000 degrees cooler. The current flyby will allow detailed comparisons to be made of the north and south polar temperatures with virtually no gap in time during the measurements.

Ulysses also discovered a high speed polar wind where the magnetic field opens up and allows pieces of the solar atmosphere to stream out at a million miles per hour. This is shown in the “clock plot” graphic above of solar wind vs. latitude. By constant monitoring of the Sun over all latitudes, Ulysses has found the Sun behaving a bit odd. The solar wind appears to be confined to latitudes above 45 degrees whereas in the previous solar cycle, the solar wind reached all the way down to the Sun’s equator.

Solar data

So what’s going on here? The Ulysses flybys hope to determine what the meaning of this is. Is it something to be concerned about in the future? The solar wind has a direct effect on Earth and Earth’s magnetic field. Data on recent solar cycles are in the graphic above and is available as a pdf file at either NASA link below. Solar activity and sunspots are driven by the solar magnetic field which changes over its 22 year cycle period. During the first flyby, the Sun’s magnetic pole in the north was positive with outward facing fields and negative at the south pole with inward facing fields. During the second orbit at sunspot maximum the poles ‘flipped’ to their opposites; negative at the north pole and positive at the south pole. The polar fields are now 50% of the strength they were during the first flyby.

The Sun is a fascinating object and more data should be available later in the year.

Graphics are from NASA.

For further information: http://ulysses.jpl.nasa.gov/ and http://science.nasa.gov/headlines/y2008/14jan_northpole.htm .

North America, South America and Western Europe will see the first lunar eclipse of 2008 on February 20 between 10:00 p.m. and 11:00 p.m. EST.

Eclipse Diagram

Diagram: NASA

This occurs mid-way between the Moon’s perigee and apogee. As a bonus, Saturn is at opposition and can be seen as a bright object just northeast of the Moon. The eclipse will take about 50 minutes. The Moon will pass in the southern-most part of the Earth’s umbral shadow, meaning the top half of the Moon will appear much darker than the bottom half which passes just inside Earth’s shadow.

There is an annular solar eclipse occurring on February 7, however, the best viewing appears to be from Antartica.

This year is leap year, which adds an extra day to the calendar tacked on to the end of February. Coincidentally this occurs in the same year as the presidential elections. So why do we have leap years?

A year is supposed to be the time it takes for Earth to go around the sun. But it falls short. About 400,000 miles short. This happens each year and after four years we adjust by adding the 29th day to February. During this “leap day” Earth will travel nearly 1.6 million miles in its path around the sun making up for the shortages in the previous three years. A leap day keeps our man made calendars in sync with the seasons and thus the reason for the leap year.

Tomorrow, January 3, Earth will be at its closest point to the sun, moving through space at 67,779 miles per hour. The speed varies depending on how the other planets and the moon are lined up as they each contribute a small braking tug due to gravity.

To be precise, a year is 365 days, 5 hours, 48 minutes and 46 seconds long – the actual length of time it takes Earth to complete its orbit around the sun. Since the year is not quite 365 and a quarter days long, after several hundred years a further adjustment would need to be made to the calendar. To help account for this quirk, a leap day is not added in years ending in “00” unless (there are always exceptions to any rule of course!) a century is evenly divisible by 400. The year 2000 was a leap year but the year 2100 will not be.