The ‘Wilson Effect’

The incredible power of a star. Solar flares and giant sunspots.

The incredible power of a star. Solar flares and giant sunspots.

In 1769 a Scottish astronomer named Alexander Wilson, working at the Macfarlane Observatory, noticed that the shape of sunspots noticeably flattened as they approached the Sun‘s limb.This was due to the solar rotation. These observations showed that sunspots were features on the solar surface, as opposed to minor planets or objects above it. Moreover, he observed what is now termed the Wilson effect: the penumbra and umbra vary in the manner expected by perspective effects if the umbrae of the spots are in fact slight depressions in the surface of the photosphere. The magnitude of the depression is difficult to determine but may be as large as 1,000 km.

This was a truly remarkable discovery during a time when the Sun was basically a mystery. Most people thought the Sun was simply “God’s Creation” and shouldn’t be questioned or resolved. Scientists had no idea what powered the Sun until the late 1800’s/early 1900’s and not until Einsteins E=mc2 paper was it confirmed to be Hydrogen fusion. Scientists in the 1700s just thought it was powered by burning coal or lumber magically placed in the center of our solar system.

Image Christian Viladrich. Source Credit: Stephen W. Ramsden

While Sunspots themselves were observed by the ancient Chinese and Meso Americans for thousands of years before Europeans, but, of course, us Europeans like to take credit for everything so when the resolution was available to detect the fact the the umbra (dark core) of a Sunspot was actually recessed down into the photosphere by up to 1000km, it was a BIG DEAL. This had enormous implications at a time when the Sun was generally regarded as a perfect creation of God with no possibility of defects or aberrations.

Nowadays, with the giant leaps in amateur solar astronomy made by companies like Lunt Solar Systems, Coronado and others YOU can now setup a small, inexpensive telescope in your yard and observe what was once a MAJOR discovery in astronomy with your very own eyes. This image from Christian Viladrich (July 2012) clearly shows the various levels of the gas that make up the Sun’s photosphere and you can plainly see what fascinated Alexander Wilson so much back in 1769. The Wilson Effect is plainly visible when a group of Sunspots nears the limb of the Sun as it rotates around (every 24-28 days). The depth of the Umbra becomes more and more visible as the spot turns more and more “sideways” to your viewing angle.

Folks, please get your family involved in science and help them to discover these things on their own. There is NO better video game on Earth than seeing into the stars for yourself. No TV show or Science channel program can even come close to experiencing these things for yourselves. Adapted from Facebook Charlie Bates Solar Astronomy Project and Stephen W. Ramsden

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