In this lesson, students will analyze data from solar magnetogram images collected over 25 years at the National Solar Observatory Vacuum Telescope at Kitt Peak, AZ. Students construct a movie of solar images for a year's worth of data. From this movie, the approximate dates of perihelion and aphelion can be estimated from changes in the relative size of the solar images viewed.

You should be able to answer the following when you have completed this exercise:

1. Determine the date of aphelion, or maximum Sun-Earth distance, in Earth's orbit from your movie.
2. Determine the date of perihelion, or minimum Sun-Earth distance, in Earth's orbit from your movie.
3. Construct movies of several years. Does the approximate dates of perihelion and aphelion remain the same for the years studied?
4. How does the date of aphelion and perihelion compare with the beginning of seasons in the northern hemisphere?

Navigate to the disk drive that contains the DASL disk.

A list of options similar to those you see to the left will appear.

Choose Magnetograms and open that folder.

Inside the Magnetograms folder are data folders with images from the years 1977 through 2002.

Choose a year by double clicking on the folder, or single clicking on it and choosing Open.

Inside each folder are magnetogram images for each date for which an image was taken. The file names indicate the year, month and date in the following format:

900101MA is the magnetogram png file for January 1, 1990.

Open any image by double clicking on the file name.

A Sequence Options window similar to the one to the left will open. The information you can learn includes:

• Number of Images: there are 264 images in the folder for this year.
• Starting Image: you can choose to begin your sequence with any numbered image. Since you want to see the entire year of images, begin with image 1.
• Increment: this option allows you to advance the images in your sequence one image at a time. You can choose to skip images by setting this at 2, 3, etc.
• File Name Contains: if you wish to only sequence images from a particular month, type the four digit number of that month in this area. March, for example, would be entered as 9003 since the files are from the year 1990.

Choose OK to build the Image Sequence.

When the image sequence has been constructed, view the year from the Stack image that appears.

View the year by holding down the right arrow on the scroll bar of the image window.

Notice that the size of the solar disk gradually changes over the course of the year.