ELi ON EARTH: Sunspots Visible in East Lansing

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Monday, October 27, 2014, 12:25 am
Aron Sousa

For the last couple of months, ELi on Earth (EoE) has been focused on the sun. EoE has covered a coronal mass ejection, the lunar eclipse, and the partial solar eclipse. Now we cover sunspots. The mainstream media has focused on the size and potential danger of a large sunspot moving across the sun this week. “The largest sunspot in decades is spitting solar flares at earth,” sputtered Time on October 24. We explain sunspots for the brainy audience of East Lansing.

Sunspots are visibly dark areas on the surface of the sun that have been observed by astronomers for more than 2000 years. Detailed observations of magnified images have been kept in the western world beginning with Galileo in the early 1600s. These records demonstrate that the sun cycles through periods of more and fewer sunspots every eleven years on average (the range is 8-14 years). Sunspots cycle in number and location on the sun.

When sunspots are plotted by year and their latitude on the sphere of the sun, the resulting pattern is called the “butterfly diagram,” as shown above. The color of the “wings” is related to the area of the sunspots – the more area, the lighter, or more yellow, the color. As you can see from the diagram, early in the solar cycle the sunspots are farther north and south of the sun’s equator, and later in the cycle the sunspots are closer to the sun’s equator.

Sunspots are darker and cooler than the rest of the sun. While most of the sun is about 5000 degrees Celsius (9000 degrees Fahrenheit), sunspots are only around 3000 degrees Celcius (about 5400 degrees Fahrenheit). Because the sunspots are cooler than the rest of the sun, they emit less visible light and are darker to observers in East Lansing. While sunspots are cooler than the rest of the sun, they have very powerful magnetic fields. And, like a magnet, they have positive and negative poles.

The large magnetic fields at sunspots lead to solar flares as well as coronal mass ejections. Solar flares are huge eruptions of energy that arc between the poles of a sunspot. As the outer surface of the sun arcs out into space and back down to the body of the sun, huge amounts of light energy spew into space. When earth is in the line of this energy spew, radio (a kind of light energy) and some other communication means can be interrupted within minutes of a flare.

Sometimes in addition to spewing light energy, sunspots eject large amounts of mass from the surface (corona) of the sun in events called coronal mass ejections. Coronal mass ejections are composed of highly energized particles that lead to impressive auroras (like the northern lights) and can disrupt not just radio waves but also the electric grid and other wired and wireless electric systems. Because the particles of a coronal mass ejection travel much slower than the speed of light, it can take a day or two for the impact of a coronal mass ejection to be noticed on earth.

Sunspot #2192 has had a couple of coronal mass ejections in the last couple of days, but it looks like sunspot #2192 will rotate away from earth before a large coronal mass ejection threatens East Lansing and our neighbors on Earth.

The first black and white image below was taken with a sun telescope in the author’s backyard. You can see the scalloped edges of the paper plate he used as a screen for the telescope. The HMI image (second one below) is from NASA’s Solar Dynamics Observatory spacecraft. It confirms the author’s observation of sunspot #2192, although the author’s sun image is flipped upside down compared to the HMI image.

The “butterfly diagram” is courtesy of NASA.

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