We have talked often in class about the fact that the Sun emits light from radio wavelengths all of the way through gamma rays, though the peak of its continuum spectrum is in the range of yellow visible light. Its appearance differs wildly over this range. Some features that are dark at visible wavelengths, glow when observed in ultraviolet and x-rays. Others which are dark in X-rays seem to glow in radio waves, still other features which are easy to see in some wavelengths are invisible in images made with other kinds of light or with different techniques. Consequently, scientists use lots of different instruments and techniques to observe the Sun. 

In December of 1995 the European Space Agency (ESA) and NASA launched SOHO, the SOlar and Heliospheric Observatory.  SOHO is in orbit around the Sun, just behind the Earth, and spends its time taking images and data at many different wavelengths.  These data can be used to study various features on the Sun, watch the Sun rotate, and observe how the Sun changes as we move from the minimum of the Sun's 11 year cycle in 1996 to its subsequent maximum and back again.

In this exercise you will have a chance to check out some of the amazing images and movies generated by the SOHO satellite while learning more about our Sun!

For this week’s homework:

Using SOHO's Glossary (and/or your textbook) and the images on the SOHO database familiarize yourself with the definition and appearance of solar promincences, sunspots, and the solar cycle as well as the wavelengths and appearances of the different EIT and MDI images. (scroll down the page to read about EIT and MDI).

1. Look around at the ultraviolet images and movies of solar prominences. At which ultraviolet wavelengths are the Sun's erupting prominences most visible? What does that tell you about the temperature of the prominences compared to the rest of the solar corona, which is many millions of degrees K in temperature?  Where in the solar atmosphere do prominences orginate (check your lecture notes here)? 

2. Use this search form to generate a seven day sequence of MDI continuum images beginning with any day you choose and working backward (note that continuum images from 2011 are only posted through January 11 at this point). Print out that sequence (you can cut/paste or draw them all on one page) and hand it in. Then draw the location of all seven sunspots on this solar grid.

Use the same search form to generate a seven day sequence for the same date in any other year available (preferably one that's a few years different).  Make a second grid like the one you did for the previous date, again being sure to also note the date and time of the image.  What can you conclude about the difference in solar activity between your two sets of data? 

3. Choose a year in which there was a lot of subspot activity (hint: look up the sunspot cycle). From a 7 day sequence, choose two groups of sunspots and plot them on a new solar grid as they move across the sun  for at least one time each day (so you should have at least seven data points per group). Label the date/time of each observation.  Once your plot is complete, compare the rotation speeds at different latitudes and comment on your results.