The Sun

©1995 The Regents of the University of California

Introduction

• It was Galileo who first noticed that the Sun does spin. And that was back in 1610!
• Let's see if you notice just as Galileo did that the Sun rotates.
• But you are going to be smarter than he was! He looked directly at the Sun and even used his telescope to study it. We now know it is DANGEROUS to look directly at the Sun, it can cause permanent eye damage.
• There are some special filters you may be able to get from your local planetarium, but do not use photographic negatives or Sun glasses. They dim the bright light but do not shield out the harmful rays that will permanently damage your eyes.
• Another option is to use a pin-hole box. If you want to make one or learn more about the filters you may use to view the Sun, click here.

Internet Information

If you are ready to investigate Mr. Sol's rotation, you may click here for a list of dates for which images in H-alpha or X-ray are available. Choose full disk images and select several images that show some type of surface feature like a sunspot, and then check images daily for a week or so.

We are curious if you will be able to tell the direction of rotation and the time it takes for the Sun to make one complete rotation.

Strategy

1. Keep careful records of all Sun images you are going to work with.

2. You can start with the image of the Sun on January 1, 1996. Notice the dark splotches?
3. Those areas are sunspots, and although they are not permanent, they last long enough for us to be able to follow them as they move with the gaseous surface of the Sun.
4. Notice and remember where these spots are.
5. Click another date to get an image of the Sun a couple of days later, on January 6, 1996, for example. Did the spot move? (Since North is up in these pictures, you should be able even to tell which direction they moved.)
6. Begin collecting data by:
   • recording the date and time of the image you work with,
   • using transparent plastic to trace the edge of the sun, and marking the North pole which appears as a tiny white hatch mark at the top of the image,
   • marking the darkest part of a sunspot,

   • comparing the locations of the sunspot on any two different images,

   • measuring the angle of rotation with the template.
7. Calculate the angular velocity and the period of rotation of the Sun by one of the methods we've discussed previously.
8. You can also take a look at an animation (7.2Mb) showing the rotation of the Sun from January 1 through November 30, 1996. This movie has one image for each day. As you can see this means that the speed of rotation that you are seeing is not representative of reality, but you can still calculate the period of rotation from this animation.

Questions

• If you pick a spot that is near the equator and figure out how long it takes to make one trip around the sun, will spots near the poles take more/less/the same amount of time?
• Are there always (from month to month or from year to year) about the same number of sunspots on the sun? Or are there times when sunspot activity is high (lots of spots and clusters of spots) and other times when the activity is low (few spots and small clusters of spots)?
• See if you can investigate to find answers to these questions, and think of some more questions of your own. Find out as much as you can about the sun. After all, it is the main source of energy for EVERYTHING that goes on here on the Earth.

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