Date: April 15, 2011

Title: Our Sun

Podcaster: Brittani Taylor and Timothy Reilly

Links: St. Vincent College

Description: Brittani Taylor from Saint Vincent College in Western Pennsylvania hopes you understand our nearest star a little more after this podcast on the history, scale and morphology of the Sun. She delights in finding new ways to express the scientific realities of solar physics in understandable terms. Have you thought about the Sun lately?

Bio: Brittani Taylor is a soon-to-be-grad, whose experience with astronomy has scratched the very surface of what’s out there. When she’s not getting informally familiar with the night sky on extended evening walks and camping trips, she wonders about her place in the big scope of things. To date, her previous experience with our skies include, at five, asking why the sky was blue, excitedly watching red moons at twelve, grumbling at the Sun during the wee college hours and, as she recalls, at one point owning a cool rocket red telescope with which she first spotted Venus. “Science is awesome,” she says. “It’s fascinating what theories and models can do for us when we put them to work.”

Narrating the essay is Timothy Reilly, a computer science major at Penn State University. This podcast has been recorded with the assistance of Matthew Deweese, a computer science major at Penn State University.

Sponsor: This episode of “365 Days of Astronomy” is sponsored by — no one. We still need sponsors for many days in 2010, so please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at


The Sun. You know, that big radiating gas ball that dictates much of how we humans live our lives. At an optimal-for-life 93 million miles away from us and making up 99.8 percent of the mass in our solar system, the Sun is beyond enormous, a virtual warehouse responsible for most all of the energy we use on Earth—we need it for life! Once we understand the spectacular size of this gas body, we can appreciate how even the smallest of its events can affect life here on earth—the sheer intensity of its power can be awe-inspiring and worrisome in some cases, and it’s these instances of solar weather and radiation that I will talk about today.

Okay, we get that the Sun is important and big, but the fact that it can affect life on Earth is by no means an exaggeration. Take for example the huge event of the February 14 solar storm of this year that heavily disrupted telecommunications in China, or look way further back at the infamous “super storm” of 1859 that impeded telegraph communication and was noted to have its own spectacular solar flare on the Sun’s surface. Yep, that’s right, from the time of the American Civil War Aurora of 1862 to the cataclysmic Halloween Storm of October 2003, there are records and speculations about past solar phenomena affecting our atmosphere that have grown more and more detailed over time.

Hopefully these few examples I’ve mentioned convince you that our massive star has some pretty awesome effects on our planet. Understanding the Sun’s magnificent power at work requires some brief overview of its inner mechanics, such as where its energies originate, its composition and the forces at play throughout it.

You probably are well aware from experience that the Sun is hot. Just go stand outside at noon and then at midnight, you’ll notice the difference, assuming you don’t live in California—well, no, even then you will notice a difference. Where does all this burning heat and energy in the form of light come from? At its very core, the giant plasma globe can reach temperatures of up to 15,000,000 Kelvin. That’s pretty hot! And we like it that way, because this intense heat combined with the density of the Sun’s gaseous core makes it possible to get hydrogen atoms to separate into nuclei and electrons, and close enough and energized enough to collide hydrogen nuclei with one another. The core is a powerhouse of nuclear fusion which is constantly taking place. Think of hydrogen as the ‘fuel’ that our Sun converts from hydrogen to helium, at a rate of four hydrogen nuclei to one helium atom. This fusion produces a byproduct of energy as well, in the form of photons, which leave the core eventually, and neutrinos, infinitesimal particles that go flying off into the nether straightaway. It’s estimated that it takes between seventeen thousand and fifty million years for photons to eventually work their way to the surface of the Sun, even though they move at the speed of light. Why? Other atoms pick up and throw away the photons in a long process known as the random walk. It’s as if there were an extremely crowded room in which you were playing hot potato, with said potato rapidly being thrown every which way in an effort to get it thrown out of the room. As you can imagine, this is a very roundabout means of escape for the energy produced. It remains in the core and is eventually diffused over the surface and into space, after going through the many respective layers of the Sun. But enough about fusion, let’s talk about some of those layers, shall we?

In addition to the core, there are five other areas of the Sun that deserve mention. Beginning after the core and reaching up to 70 percent of the Sun’s radius is the radiative zone of the Sun, aptly named because of its properties of radiating energy outwards by of electromagnetic radiation in the form of aforementioned photons. Temperatures vary from five million to ten million Kelvin.

Above the radiative zone is the convection zone, with temperatures peaking at around 2 million Kelvin. Energy moves differently here, and rather than radiating, giant blobs of plasma heated by the radiative layer carry heat upwards with them. They break surface as granules in a specific layer known as the photosphere, what we know as the “surface” of the sun. Earthly observations show that photos of these granules can be likened to watching a pot of boiling sugar, or molasses—only the granules boil and “pop”at about a rate of 10-20 minutes per bubble, if you will. The dark edges of the granules are the result of cool plasma sinking down into the Sun, whereas hotter regions rise and are brighter. This is evidence of the aforementioned convection. What we can “see” happening on the Sun’s surface without aid of equipment is the photosphere. At a comparatively cool 5,800 Kelvin, the photosphere extends 500 kilometers deep, but is relative in thickness to a thin sheet of tissue paper covering a bowling ball!

In what we call the Sun’s atmosphere, there remain two other layers. The chromosphere just above the visible layer of the Sun begins at about 4,300 Kelvin at its lowest point. Contrary to the decreasing pattern of temperature apparent elsewhere, the heat actually rises to 50,000 Kelvin. Why this happens remains a somewhat obscured mystery to scientists, who speculate about the role of the Sun’s magnetic currents in producing these conditions. It only becomes hotter from here: the corona, or “crown” just after the transitional region of the chromosphere has a temperature ranging from 500,000 Kelvin to 2 and 3 million Kelvin! This extremely dim and very much low density plasma can be seen during total solar eclipses, and gives us a glimpse into the beginnings of the solar winds that extend throughout the entirety of our solar system.

The solar winds are demonstrable evidence of the Sun’s magnetic fields, which are projected far, far into our solar system as a type of bubble (heliosphere, if you will) until it mixes with other output in interstellar space. The magnetic field of the Sun itself is an extensively involved topic of its own right. Like our planet, the Sun has its own north and south poles, and its own magnetic sphere. The similarities end here however, as the Sun’s magnetism is double the strength of our own fields. This power combined with the fact that the highly ionized gas is a perfect conductor means that the magnetic fields are more or less tied to the plasma itself. This means that all solar weather and abnormality is in part governed by the force of the magnetic field lines’ behavior. What is so odd about these lines? As a gas body the Sun cannot maintain a rigid structure to allow constant rotation along all points of its surface. Because of this, the speed at which different latitudes of the Sun rotate is variable: latitudes close to the equator rotate faster, whereas the north and south poles rotate slower. This differential rotation causes the magnetic field lines, which are tied to the ionized gases to become twisted upon themselves. Imagine the Sun as a giant Rubik’s sphere that is being twisted in the center much faster than its top and bottom. In addition to this, the inside of the Sun moves at a faster rate than the outside. Eventually, the magnetic lines become so coiled up that they cause tension and disruptions on the surface in the form of a sort of rope-like tube guided by this magnetic force. We know this as the cause of the Sun’s weather. This coiling up of the magnetic field lines becomes more complex over a course of 11 years until at some point the adjacent regions of the Sun are dominated by opposite direction magnetic fields. The instability leads to adjacent areas being forced to change their directions to align with neighboring regions. In this process magnetic north and south reverse. The process begins again, and it actually takes a total of 22 years, give or take, for the Sun to reset itself. As of the present, we still have questions about the nature of the Sun’s magnetic fields and are hopeful that learning more about them will help us understand solar weather and sunspot occurrence.

Scientists have been able to see that the magnetic fields of the Sun give shape to the corona that is blown off into the solar wind and serve as the current that carries matter from the Sun to Earth and the other planets. This wind is why comets have a tail that is always opposite the Sun. This means that the Sun is losing material, an amount estimated to be 107 tons per second of matter! But don’t worry, this is quite a tiny amount in comparison with the huge star, and the Sun has enough fuel to remain as it is at present for another 5 billion years. Nevertheless, this low density gas is powerful, and ranges from speeds of three hundred to eight hundred and even one thousand kilometers per second! Researchers and engineers have looked upon the power of the solar wind with the intention of harnessing it in order to propel spacecraft with solar sails. Very recently the Japan Aerospace Exploration Agency has extended the mission time of its kite craft named IKAROS after stunning success with the technology for a year, proving that there is much promise for humans to take advantage of Sun energy. At the same time as this promise remains the concern and watchful eye of scientists upon less-than-favorable phenomena for humans, called solar storms.

Solar storms can be correctly referred to as any and all occurrence of abnormalities on the Sun’s surface. This includes sunspots, solar flares, prominences and coronal mass ejections. Sunspots are sometimes thought to be linked with Sun’s magnetic fields as they twist into, as I’ve said, rope-like tubes which break the chromosphere and coronal surface of the Sun, forming sunspot pairs when the rope twists back down into the Sun. This phenomenon produces active regions on the Sun which can lead to other explosive results. The planet-sized blemishes form over a period of days and weeks, and can last for months. Sunspots are named as such because of their dark appearance in relation to the Sun because they are cooler in comparison at about 4,000 Kelvin. The dark inner section is the umbra while the light surrounding region is called the penumbra.

Sunspots oftentimes lead to solar flares, which are bright, intensely hot eruptions from the Sun that are projected thousands of miles from its surface as magnetic lines snap in reconnection. They rise in minutes, and decay in hours in a flash of an explosion. The resulting sunquakes emit energy a million times greater than any volcano on earth, or 40,000 times greater than the 1906 San Francisco earthquake. You get the picture. It’s big. Solar prominences are arcs of gas being manipulated by magnetic fields that can be held up hundreds of thousands of miles from the Sun’s surface for many months. Most will erupt in their lifetime and spill their material into space. Prominences seen from above the Sun’s surface, not on its side are referred to as filaments.

Finally we arrive at Coronal Mass Ejections, which are the most massive plasma bursts to issue from the Sun. CMEs, as they are called, move along magnetic field lines and release a burst of magnetic field and plasma upon eruption that can be absolutely devastating to electric dependent equipment; about 20 billion tons of matter can be spat out.

This all sounds scary, but it’s more important to focus on a specific types of radiation from the Sun. Scientists are wary but alert thanks to the Sun weather reports of the NOAA. The energy in the form of radio, gamma, X-ray and ultraviolet radiation can be highly damaging and deadly in high doses for humans for the latter three. Radio waves can disrupt planes, satellite and other communications, and gamma and X-Rays are deadly to life. Thankfully, our atmosphere and our own magnetic field protect us from the worst of this danger. In fact, besides worries over electromagnetic “static disruptions” a CME or solar event can lead to beautiful auroral patterns from photon excitation of our atmosphere as well. Humans on the Earth’s surface should probably worry more about the case for UV radiation, as in recent years the ozone layer that serves to protect us from it has been eroded—which is more worrying than any solar phenomena. Not only is UV radiation a more daily worry, but it is a more widespread one for the entirety of the biosphere, not just man. In 2007, it was eight to nine times more likely that you’d contract skin cancer than have to worry about your plane being involved in a fatal accident. So, with the knowledge of the awesome power of our Sun in mind, we should temper this concern with the more pertinent one of daily UV radiation that reaches us every day. Hopefully, with our knowledge and observations of the Sun we can temper some of our fear and worry more about putting on sunscreen than being caught off guard by the Sun.

So now you know. This is Brittani Taylor from Saint Vincent College signing

End of podcast:

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