Tag Archives: sun

Solar Tornadoes

No, Solar tornadoes are not another manifestation of our slowly warming planet. Rather, these phenomena are believed to explain why the outer reaches of the solar atmosphere are so much hotter than its surface.

[div class=attrib]From ars technica:[end-div]

One of the abiding mysteries surrounding our Sun is understanding how the corona gets so hot. The Sun’s surface, which emits almost all the visible light, is about 5800 Kelvins. The surrounding corona rises to over a million K, but the heating process has not been identified. Most solar physicists suspect the process is magnetic, since the strong magnetic fields at the Sun’s surface drive much of the solar weather (including sunspots, coronal loops, prominences, and mass ejections). However, the diffuse solar atmosphere is magnetically too quiet on the large scales. The recent discovery of atmospheric “tornadoes”—swirls of gas over a thousand kilometers in diameter above the Sun’s surface—may provide a possible answer.

As described in Nature, these vortices occur in the chromosphere (the layer of the Sun’s atmosphere below the corona) and they are common. There are about 10 thousand swirls in evidence at any given time. Sven Wedemeyer-Böhm and colleagues identified the vortices using NASA’s Solar Dynamics Observatory (SDO) spacecraft and the Swedish Solar Telescope (SST). They measured the shape of the swirls as a function of height in the atmosphere, determining they grow wider at higher elevations, with the whole structure aligned above a concentration of the magnetic field on the Sun’s surface. Comparing these observations to computer simulations, the authors determined the vortices could be produced by a magnetic vortex exerting pressure on the gas in the atmosphere, accelerating it along a spiral trajectory up into the corona. Such acceleration could bring about the incredibly high temperatures observed in the Sun’s outer atmosphere.

The Sun’s atmosphere is divided into three major regions: the photosphere, the chromosphere, and the corona. The photosphere is the visible bit of the Sun, what we typically think of as the “surface.” It exhibits the behavior of rising gas and photons from the solar interior, as well as magnetic phenomena such as sunspots. The chromosphere is far less dense but hotter; the corona (“crown”) is still hotter and less dense, making an amorphous cloud around the sphere of the Sun. The chromosphere and corona are not seen without special equipment (except during total solar eclipses), but they can be studied with dedicated solar observatories.

To crack the problem of the super-hot corona, the researchers focused their attention on the chromosphere. Using data from SDO and SST, they measured the motion of various elements in the Sun’s atmosphere (iron, calcium, and helium) via the Doppler effect. These different gases all exhibited vortex behavior, aligned with the same spot on the photosphere. The authors identified 14 vortices during a single 55-minute observing run, which lasted for an average of about 13 minutes. Based on these statistics, they determined the Sun should have at least 11,000 vortices on its surface at any given time, at least during periods of low sunspot activity.

Due to the different wavelengths of light the observers used, they were able to map the shape and speed of the vortices as a function of height in the chromosphere. They found the familiar tornado shape: tapered at the base, widening at the top, reaching diameters of 1500 km. Each vortex was aligned along a single axis over a bright spot in the photosphere, which is the sign of a concentration of magnetic field lines.

[div class=attrib]Read the entire article after the jump.[end-div]

[div class=attrib]Image: A giant solar tornado from last fall large enought to swallow up 5 planet Earths is the first of its kind caught on film, March 6, 2012. Courtesy of Slate / NASA /Solar Dynamics Observatory (SDO).[end-div]


Cool Images of a Hot Star

Astronomers and planetary photographers, both amateur and professional, have been having an inspiring time recently in watching the Sun. Some of the most gorgeous images of our nearest star come courtesy of photographer Alan Friedman. One such spectacular image shows several huge, 50,000 mile high, solar flares, and groups of active sunspots larger than our planet. See more of Freidman’s captivating images at his personal website.

According to MSNBC:

For the past couple of weeks, astronomers have been tracking groups of sunspots as they move across the sun’s disk. Those active regions have been shooting off flares and outbursts of electrically charged particles into space — signaling that the sun is ramping up toward the peak of its 11-year activity cycle. Physicists expect that peak, also known as “Solar Max,” to come in 2013.

A full frontal view from New York photographer Alan Friedman shows the current activity in detail, as seen in a particular wavelength known as hydrogen-alpha. The colors have been tweaked to turn the sun look like a warm, fuzzy ball, with lacy prominences licking up from the edge of the disk.

Friedman focused on one flare in particular over the weekend: In the picture you see at right, the colors have been reversed to produce a dark sun and dusky prominence against the light background of space.

[div class=attirb]Read more of this article here.[end-div]

[div class=attrib]Image: Powerful sunspots and gauzy-looking prominences can be seen in Alan Friedman’s photo of the sun, shown in hydrogen-alpha wavelengths. Courtesy of MSNBC / Copyright Alan Friedman, avertedimagination.com.[end-div]

Once Not So Crazy Ideas About Our Sun

Some wacky ideas about our sun from not so long ago help us realize the importance of a healthy dose of skepticism combined with good science. In fact, as you’ll see from the timestamp on the image from NASA’s Solar and Heliospheric Observatory (SOHO) science can now bring us – the public – near realtime images of our nearest star.

[div class=attrib]From Slate:[end-div]

The sun is hell.

The18th-century English clergyman Tobias Swinden argued that hell couldn’t lie below Earth’s surface: The fires would soon go out, he reasoned, due to lack of air. Not to mention that the Earth’s interior would be too small to accommodate all the damned, especially after making allowances for future generations of the damned-to-be. Instead, wrote Swinden, it’s obvious that hell stares us in the face every day: It’s the sun.

The sun is made of ice.

In 1798, Charles Palmer—who was not an astronomer, but an accountant—argued that the sun can’t be a source of heat, since Genesis says that light already existed before the day that God created the sun. Therefore, he reasoned, the sun must merely focus light upon Earth—light that exists elsewhere in the universe. Isn’t the sun even shaped like a giant lens? The only natural, transparent substance that it could be made of, Palmer figured, is ice. Palmer’s theory was published in a widely read treatise that, its title crowed, “overturn[ed] all the received systems of the universe hitherto extant, proving the celebrated and indefatigable Sir Isaac Newton, in his theory of the solar system, to be as far distant from the truth, as any of the heathen authors of Greece or Rome.”

Earth is a sunspot.

Sunspots are magnetic regions on the sun’s surface. But in 1775, mathematician and theologian J. Wiedeberg said that the sun’s spots are created by the clumping together of countless solid “heat particles,” which he speculated were constantly being emitted by the sun. Sometimes, he theorized, these heat particles stick together even at vast distances from the sun—and this is how planets form. In other words, he believed that Earth is a sunspot.

The sun’s surface is liquid.

Throughout the 18th and 19th centuries, textbooks and astronomers were torn between two competing ideas about the sun’s nature. Some believed that its dazzling brightness was caused by luminous clouds and that small holes in the clouds, which revealed the cool, dark solar surface below, were the sunspots. But the majority view was that the sun’s body was a hot, glowing liquid, and that the sunspots were solar mountains sticking up through this lava-like substance.

The sun is inhabited.

No less a distinguished astronomer than William Herschel, who discovered the planet Uranus in 1781, often stated that the sun has a cool, solid surface on which human-like creatures live and play. According to him, these solar citizens are shielded from the heat given off by the sun’s “dazzling outer clouds” by an inner protective cloud layer—like a layer of haz-mat material—that perfectly blocks the solar emissions and allows for pleasant grassy solar meadows and idyllic lakes.