Skip to content

solar differential rotation [try it]


The Sun is giant fluid ball of gas. It is not a solid body, and it does not behave like one. In particular, it rotates at different speeds at different latitudes.

The website displays daily collections of solar images ranging from visible light photospheric images to magnetic maps to high-energy X-ray images of the corona. You can look up what the Sun looked like on any day going back years.

There are a couple of interesting things about these images: first, you can clearly see sunspots and active regions, and second, there is a nice grid superposed on the images. Which means it is possible to track features on the Sun as they rotate along. Here’s an example from Hinode/XRT data from 2010-apr-30 to 2010-may-02; pay special attention to the active region 11064 and the unnumbered feature north of it.

Can you tell how fast the Sun rotates? Can you discern a variation with latitude?

Do sunspots stay fixed, or do they morph and evolve? What strategy would you use to avoid getting a bad measurement simply because the spot you were tracking decided to speed up, go in reverse, disappear, or evolve?

Real data are messy, with gaps when observations couldn’t be made, and times when something went wrong with the exposure, and features that change in shape and intensity at the most inconvenient times, etc. What can you do to alleviate such problems?