The Sun is a dynamic astrophysical object, and it is often easier to understand when looking at how it is changing.  This is the idea behind difference images.  You take an image of the Sun at one time, and subtract from an image at another time, and look at the difference.  The difference image shows you what has changed between one time and another.  Traditionally, difference images are shown in grayscale, with lighter values indicating a positive change – something got brighter – and darker values indicating a negative change (something got darker).

Helioviewer.org provides two types of difference images: running difference, and base difference.  With running difference images, the current image is subtracted from an image some short interval earlier.  For example, making a running difference movie with an interval of 15 minutes allows you to see how much the Sun has changed compared to 15 minutes ago. This allows you to see the dynamic, running changes in emission from the Sun.

With base difference images, the current image is subtracted from an image at some fixed earlier time. This allows you to see the total change compared to that earlier time.

Both types of images and movies are useful scientifically.  Please see the user guide for more information on difference images.

If you encounter any bugs in this new functionality, or for any other questions, please contact us at contact@helioviewer.org.

An example running difference movie showing the evolution of a flaring limb active region.

A zoom in on the same region for the same time range as above, but this time using a base difference.