Warren Wilson College

Physics Photo of the Week

September 22, 2006

Lonely Sunspot

Every year the Astronomy class at Warren Wilson College photographs the sun looking through a telescope to examine sunspots, and we usually see several.  This week, however, we could only find one sunspot.  The lonely sunspot is located at about "8:00 o'clock" in the photo about halfway from the center of the image to the limb or edge of the sun's disk.

The photo at right, taken exactly two years ago today (Sept. 22, 2004) by Simon Johnson shows a much larger sunspot in approximately the sameplace in the image.  Finally, below is an enlargement of that major sunspot from two years ago.

All these phoros were taken with a digital camera attached to the eyepiece of an 8-inch telescope.  The telescope was fitted with a special filter that blocks out most of the blinding sunlight, otherwise the detector in the camera would be ruined.

The major reason for the lack of sunspot activity in the fall of 2006 (compared with two years ago) is that 2006 is the low point of the 11 year sunspot cycle.  For some mysterious reason - not fully understood - the number of sunspots on the sun fluctuates in the familiar 11 year cycle.

Sunspots are known to consist of major magnetic storms penetrating the surface of the sun.  There are strong magnetic field lines directed out of or into each sunspot.  Charged particles (electrons and protons) are better able to escape the Sun's surface along the magnetic field lines, and thus cool the surface.  The center of a sunspot is about 1000 degrees K cooler than the surrounding photosphere (6000 degrees K).  Hence sunspots are not black, they are merely darker.

This year's astronomy students estimated that the small sunspot in the large photo representing this year's sunspot is about the diameter of Earth's Moon.  The large sunspot from two years ago is about the size of the Earth.

Large picture file to load - Please be patient!One of the major reasons for photographing sunspots is to give astronomy students an opportunity to measure the rotation rate of the Sun.  The animated photo at left shows the parts of two images of the Sun: Monday, September 18, 2006 and Wednesday September 20 (the image from the top of the page).  The Monday image shows the sunspot closer to the Sun's limb.  The apparent motion of the sunspot location between the two days is due to the rotation of the Sun.  Colin Duke assisted with the photography of the September 18 image.

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature an interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to dcollins@warren-wilson.edu.

Click here to see the Physics Photo of the Week Archive.

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