Tracking the Movement of Sunspots

Tracking the Movement of Sunspots


For this activity, you will track the location of sunspots on the sun over a two-week period. To discover various characteristics of the sun, you need to observe it. Your “eyes” for observing the sun will be the SOHO spacecraft currently circling the sun about one million miles away from earth.

SOHO is equipped with 12 specialized scientific instruments that collect information about the sun by taking solar images. Some instruments look at the entire solar disc, others zero in on a particular aspect of the sun. These instruments explore everything about the sun from its corona to the violent magnetic eruptions on its surface to the sound waves that help us understanding the mysteries of the sun’s deep interior.

By tracking the location of sunspots over a continuous two-week period, you will be able to observe how sunspots change and move as the sun rotates over time.


1. Every day, using the Web, you should print out a copy of a solar image taken by the MDI instrument. If you don’t have access to the Web or a printer, your teacher will provide a class set of images. Using a latitude/longitude grid of the sun, provided to you by your teacher, you will record the location of each sunspot.

2. Choose the type of image you will study
The SOHO MDI instrument takes two types of images:

  • Intensitygrams are pictures of how bright the sun is. Because sunspots are cooler than the surrounding regions, they show up as black splotches. An example of an intensitygram is shown in Figure 1. (or at http://sohowww.nascom.nasa.gov/data/summary/gif/011030/smdi_igram_fd_20011030_0800.gif )
  • Magnetograms are images of the sun’s magnetic field strengths. Sunspots are magnetic eruptions—these eruptions are called active regions. These active regions show up on magnetograms as large black and white areas. An example of a magnetogram is shown in Figure 2. (or at http://sohowww.nascom.nasa.gov/data/summary/gif/011030/smdi_maglc_fd_20011030_0200.gif )

Two things to note about the images:

  • Not all active regions are sunspots but many of them are.
  • Intensitygrams show primarily sunspots; magnetograms show active regions.

Sunspots last longer than active regions—sunspots can live up to 30+ days whereas active regions generally remain for five or so days.

You can choose to study either intensitygrams or magnetograms for the two-week period. Whatever type you choose, make sure you stay with that type throughout the activity. Do not switch between the two types of images!

Photo Credit: Courtesy of SOHO/[instrument]
consortium. SOHO is a project of international
cooperation between ESA and NASA.
Photo Credit: Courtesy of SOHO/[instrument]
consortium. SOHO is a project of international
cooperation between ESA and NASA.
Figure 1 Intensitygram  Figure 2 Magnetogram

3. Printing Images

Images can be obtained from SOHO’s official site at: http://sohowww.nascom.nasa.gov/cgi-bin/get_soho_images?summary/.

When you look at the image list, the images will be labeled like so:

  • SOHO MDI, Magnetogram, longi. comp., Full Disk
  • SOHO MDI, Intensitygram, Full Disk

Choose either the intensitygram or magnetogram and print out the image.

The MDI instrument takes pictures of the sun every 96 minutes. Thus, there may be more than one image available for a single day. Pick the image taken earliest in the day (there will be a time given with each image.)

You will notice that there are white boxes in the center of the images. Ignore these when you make your observations.

4. Tracking Sunspots
For your first image, you will need to first identify your sunspots. Identify only the large blotches and don’t worry about the smaller scattered dots. Use letters or numbers to identify your sunspot clusters. You can write directly on the image.

Place the latitude/longitude grid (this will be a clear transparency) directly on top of the image. Using the grid, record the latitude and longitude of your sunspots. You should measure to the center of the spot group. In magnetograms, you will need to measure to the center between the black and white portions (see Figure 3).

Images courtesy of SOHO (ESA & NASA)


Figure 3. Measuring sunspots in magnetograms

5. Recording Data
Use the “Sunspot Data Recording Worksheet” to record your measurements. You will need a new table for each day’s observations.

Record the following information for each day’s observations:

  • The name of each sunspot group
  • The latitude and longitude of each sunspot group
  • Description and observations of the sunspot group (Has the group changed size or shape? Has the group disappeared all together?)

You must collect a minimum of 10 solar images over a two-week period. Go to the SOHO site daily since on some days, there are no images available to view.

This project begins on ___________________ and ends on __________________.

I will study the following images taken daily by the MDI instrument:

Magnetogram          Intensitygram
(circle one)

I must bring all my images and data tables to class for a final summary on ______________.

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