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About "Ask A Scientist!"

On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 5 February, 2004 Next Week's Question
Inconsistent magnetic field causes sun's black spots
Question
Why does the sun have black spots?

Question
Black spots, or sunspots, are among the most interesting and amazing phenomena observed on the Sun. The origin of sunspots has been a great puzzle for scientists throughout the centuries. There is evidence that ancient people knew about sunspots. Astronomers in ancient China kept a pretty good record of dark spots on the Sun more than two thousand years ago. The Greeks also mention sunspots in their writings from about the same time. These early astronomers could rely only on their eyes to see the Sun. It was possible to look at the Sun during the sunset (even though looking directly at the Sun is very dangerous anytime!). When the first telescopes were invented in 1609, four astronomers from Holland, Italy, Germany and England started making systematic observations of sunspots. Some of them thought that the sunspots were small planets orbiting the Sun. Others thought that the spots were part of the Sun. Italian astronomer Galileo Galilei, made many observations and drawings of the spots and concluded that they were probably clouds on the Sun. Many astronomers saw that sunspots appeared, moved in the direction of the equator, and then disappeared.

Sunspots come in all sizes. Some of them are very big, about the size of Earth, and others are much smaller. They all look small to us, because the Sun is far away from our planet. Scientists back then were really puzzled about their origin, and remained puzzled for another few centuries, until recent times, when new telescopes helped us understand what they are. Special solar telescopes were sent to space to observe the Sun and sent back many nice pictures. Now we know the structure of the sunspots in great detail. The spots look like craters: they are darker in the center and have a lighter rim around them. Scientists now understand that the spots look black because they are cooler than the rest of the surface of the Sun.

The formation of sunspots has to do with the magnetic field of the Sun. All planets and stars have a magnetic field. The Earth has a magnetic field which moves a compass arrow so that it always points to the North. The Sun's magnetic field is not that simple: it is very strong in some regions, and much weaker in other regions. In some regions it is a thousand times larger than the Earth's magnetic field. These regions of strong magnetic fields are where we find sunspots! Moreover, the spots often come in pairs. These pairs act like a bar magnet: one of spots corresponds to the North Pole and other to the South Pole of the bar. Walking with a compass on the Sun would be confusing; the compass would always show the direction to a nearby sunspot. Since most of the spots are located right above and below the Sun's equator, a compass arrow would usually point East or West. However, the compass would point in different directions in different regions of the Sun.

Why are spots cooler in the region of the strongest magnetic field? This is because the upper layers of the Sun are in constant motion, like bees in a hive. This motion helps bring heat from inner regions up to the surface and makes the surface hot. But a strong magnetic field slows down this motion and prevents heat from moving up to the surface. The lowest temperature in the sunspots is about 3,700 Kelvin, which is about 6,200 degrees Fahrenheit. This temperature may seem very high, but it is much lower than the temperature of the rest of the solar surface, which is 5,700 Kelvin, or more than 9,800 degrees Fahrenheit. Thus, the spots look black in comparison with the nearby hotter regions of the Sun.

It is amazing how much people have come to understand about sunspots and other events on the Sun. You can observe sunspots using ordinary binoculars or a small telescope, but NEVER look through them with your eyes. The Sun is very bright and will hurt your eyes. However, you can project the image of the Sun on a piece of paper, and then you will see the spots on the paper!