Examine Images for Differences in Different Color Filters


In this activity, students will use the HOU-IDL software to qualitatively and quantitatively analyze FITS format telescope images for differences in the appearance of a deep sky object as it appears through different color filters. Images may be ones students have obtained as part of this activity or images selected from the HOU image database.


The procedure for this activity is as follows:

1. Download your chosen/requested images from the HOU image database.

2. Use figure 2 to determine what filter and exposure time was used for each image.

3. Open your images in HOU-IDL. You may rename your files if you wish (example: 'NGC 2419 Red.fts') and then save. Be careful HOU-IDL is saving your files in the correct location on your computer.

4. Perform some image processing to adjust contrast/display of image (Keep Display in Grayscale Or Inverse Greyscale)

5. Save your images as JPEG files and post to the class work area on the Collaboratory OR Print copies of the images (CHANGE DISPLAY TO INVERSE GREYSCALE)

6. Describe/Detail differences in the appearance of your object.


Record the differences in your object's appearance by making notes either in your Collaboratory class work area or directly on the printed images. Some possible things to look for include differences in apparent size of your object, differences in the appearance of specific features, differences in number of stars, or differences in the brightness of individual stars. Observations should be both qualitative and quantitative using HOU-IDL tools such as Aperture and Slice.


Students can discuss the observations they have made of their objects. Possible questions to consider:

1. Through what filter is there the largest difference between images of the same object?

2. What types of objects vary most in appearance between different filters?

3. What could explain the differences?