Observing Sunspots on the Sun's Surface Using Images from the SOHO Spacecraft

CONCEPT

Images from the highly sophisticated spacecraft, SOHO, circling the sun about 1,000,000 miles from Earth towards the sun. We will use SOHO images to observe and record information about the currently visible sunspot groups. These images will be downloaded from the SOHO website located on the Internet.

VOCABULARY

Sunspot - a dark spot on the sun's surface caused by the cooling of the sun's surface by very intense magnetic fields. They occur when a strong magnetic field rises from below the surface of the sun. They are darker than the rest of the solar surface (photosphere) because they are cooler. Most of the visible surface has a temperature of about 9700º Fahrenheit, but big sunspots can drop to about 7000º.

SOHO Space Craft - the Solar and Heliospheric Observatory, a spacecraft that was specially designed to observe and study the sun.

Michelson Doppler Imager (MDI) - images from SOHO that are taken in the in the deep red region of the spectrum. The most prominent solar features are the sunspots on the solar photosphere. This is very much how the sun looks like in the visible range of the spectrum.

Polar Coordinates - a way to describe with numbers every spot on a sphere, like the sun or Earth. The circles that are drawn on the surface of the sphere are called the latitude and longitude. Latitude circles are drawn around the sphere and longitude circles are drawn from the poles at the top to the bottom of the sphere.

Sunspot Data Recording Worksheet - a worksheet to record information about what we see when looking at the sunspots on the images of the sun downloaded from the SOHO spacecraft.

Speed of Revolution - how fast a sphere is rotating about its axis.

Solar Day - the number of Earth days for the sun to revolve once on its axis.

OBJECTIVES

Students will learn how to use the Internet to access and download information about the sun that is current to within 24 hours of when it was observed by the SOHO spacecraft. The systematic observing and recording of data about sunspots will teach the students the value of good experimental processes. The recorded data can be used to estimate the speed of revolution of the sun.

MATERIALS

• A personal computer with access to the Internet and a printer
• Images of sun every day, for about 2 weeks, downloaded from the SOHO website
• Sunspot recording worksheet
• Latitude/longitude grids, copied onto a transparency if possible.

PROCEDURE

1. Use the personal computer to connect to the Internet and access the website, http://sohowww.nascom.nasa.gov/data/realtime-images.html

2. Select from the list of images one that is labeled an "MDI Continuum." Print the image. If a printer is not available, try to sketch the image from the screen using the latitude/longitude grid that has been copied onto a transparency.

3. For each of the major sunspot groups, record on your sunspot recording worksheet:

   a. The name of each spot group. Make up any name you want, but make sure to keep track of which group has which name so the data you record is consistent. Note where the spot groups lay, i.e. latitude and longitude.

   b. Note whether there were any observable changes in your sunspot groups, i.e. size, shape, appearance and disappearance.

4. Collect images and record data for 10 consecutive days. Weekend data can be collected on the following Monday by going back in the image file using the previous day button.

   a. Try to get images from roughly the same time each day.

   b. Work with only the large dark areas; do not use smaller black dots.

   c. When measuring the latitude and longitude, use the center of the sunspot group, the larger dark areas.

5. Using the data you have collected, go to the activity; calculate the sun's speed of rotation.

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