This lab exercise is intended to provide you with insight into major solar features as well as an understanding of the sizes of these features. You will asked to examine a number of solar images - these will be available in both paper form (to include as part of your report) as well as in electronic form for analysis using on-line tools.

Materials and Resources

  • access to Stellarium
  • access the applet Solar Scale Calculator
  • an image manipulation program (Microsoft Paint on PCs or GIMP on Macs are good choices)
  • paper copies of solar images from The King's University Observatory


  1. Please select the following images and be sure to note the image scale that is shown in the table below. When the image is displayed "right-mouse-click" on the image and save it to your local hard drive (make sure you note which directory it is being saved in!) - it would be a good idea to save it into your "My Documents" folder .
Image # Image Info Image
1 Image taken September 5, 2017 in white light using a neutral density filter. Image scale is 1.36"/px
2 Image taken September 5, 2017 in white light using a neutral density filter. Image scale is 1.36"/px
3 Image taken August 17, 2017 in Hydrogen-alpha light. Image scale is 1.93"/px
4 Image taken June 25, 2017 in Hydrogen-alpha light. Image scale is 0.97"/px
5 Image taken August 21, 2017 in white light. Image scale is 1.79 "/px
  1. Open your favourite image analysis program as well as Solar Scale Calculator. You will need these applets to help analyze your solar images. In this example we will use Microsoft "Paint" which is part of any Windows system. If you are using a Mac then GIMP is a good choice. All you need to be able to do is to draw a straight line on the image that you are investigating and get from this the " X length " and " Y length" for the line.
  2. Use Paint (or similar program) to open one of the images that you have saved in your "My Documents" folder


  1. Be sure to look up the distance between the earth and Sun for the date on which each image was taken. Use Stellarium to do this. The distance will be given in AU - you can use the applet solar Scale Calculator to enter the distance in AU. You will also need to enter the scale of the image in seconds or arc per pixel ("/px). Finally, enter the initial and final x,y values of the feature in pixels and press the calculate size button. The resulting size will be shown in units of kilometers.



For each of the images that you chose please do the following:

  1. Prepare a table in which identify by letter or number at least 2 features on each of the images that you wish to measure. Carefully note this on the hard copy (which will handed in along with the report) as well as in the table. Be sure to record the image scale and the size of the feature in both pixels and kms.
Image Name
scale = ("/px), Solar Distance (AU)
Feature Size (px) Size (km)


  1. From your analysis be sure to comment on:
    • diameter of the sun
    • the size of sunspots
    • appearance and size of solar prominences
    • extent of the solar corona
    • evidence for and size of solar plages
    • Image #4 shows the solar chromosphere as a distinctly reddish layer surrounding the sun. Estimate the depth of the chromosphere.
    • evidence that the sun is a "magnetic environment"
  2. (It would be a good idea to organize and discuss each of the above under a sub-heading in the analysis section of your report)

  3. Prepare a conclusion in which you provide a summary of what you have learned about the sun. Did any of what you found surprise you?

What to Hand in and When

This lab project is due in 2 weeks. The exercise will be graded as follows:

Neatness and format:

  • Useful headings
  • grammar and spelling
  • typed and followed format

Discussion of Data

  • number of features discussed
  • insight into the features and what they mean
  • variety of solar features that you investigated

Introduction and Conclusions

  • what do you intend to do in this lab investigation?
  • what insights about the sun do your data suggest - spend some time discussing what you have discovered and suggest other things that the data may tell us.


Be sure to use a formal report style (separate cover page and proper use of headings and table/figure annotations).

Reminder - what report style looks like:

  1. all tables should be numbered and labelled as Table 1 (with caption), Table 2 (with caption) etc
  2. all figures should be numbered and labelled as Figure 1 (with caption), Figure 2 (with caption) etc
  3. report should have an Introduction, Data, Analysis and Conclusion section - each of which is identified by an appropriate heading
  4. no point form sentences - you must write in complete sentences (and yes - spelling and grammar count!)
  5. report MUST be typed - no handwritten submissions please