# sunspots - 11 year activity cycle

**URL:** <https://boards.straightdope.com/t/sunspots-11-year-activity-cycle/213260>\
**Category:** Factual Questions\
**Created:** [November 14, 2003, 4:14pm UTC](https://boards.straightdope.com/t/sunspots-11-year-activity-cycle/213260 "2003-11-14T16:14:43Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Knighted\_Vorpal\_Sword](https://avatars.discourse-cdn.com/v4/letter/k/ac91a4/32.png) [@Knighted\_Vorpal\_Sword](https://boards.straightdope.com/u/Knighted_Vorpal_Sword)\
**Post date:** [November 14, 2003, 4:14pm UTC](https://boards.straightdope.com/t/sunspots-11-year-activity-cycle/213260/1 "2003-11-14T16:14:43Z")

</div>

Has anyone figured out why there seems to be an 11 year activity cycle for sunspots?

---

<div class="post-metadata">

**Author:** ![GawnFishin](https://avatars.discourse-cdn.com/v4/letter/g/e9bcb4/32.png) [@GawnFishin](https://boards.straightdope.com/u/GawnFishin)\
**Post date:** [November 14, 2003, 5:00pm UTC](https://boards.straightdope.com/t/sunspots-11-year-activity-cycle/213260/2 "2003-11-14T17:00:29Z")

</div>

It is basically because the sun rotaion. It is kind of wierd the central or “equatorial” region of the sun rotates faster than at higher latitudes. So the equator rotates every 25 days and approximately 30 days for polar regions. The rotation is also affected by depth. The interior rotates slower than the equator and it is this differential rotation that causes the sun spot cycle. Which is 22 years, every 11 years the magnetic field is reversed so a full magnetic cycle is 22 years.

---

<div class="post-metadata">

**Author:** ![GawnFishin](https://avatars.discourse-cdn.com/v4/letter/g/e9bcb4/32.png) [@GawnFishin](https://boards.straightdope.com/u/GawnFishin)\
**Post date:** [November 14, 2003, 5:39pm UTC](https://boards.straightdope.com/t/sunspots-11-year-activity-cycle/213260/3 "2003-11-14T17:39:24Z")

</div>

This [site](http://faculty.salisbury.edu/~jwhoward/astro108/html/lec7.htm) has a good picture of the ‘Babcock model’ and explains in a lot more detail than I have time for a the moment.

---

<div class="post-metadata">

**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\
**Post date:** [November 14, 2003, 10:02pm UTC](https://boards.straightdope.com/t/sunspots-11-year-activity-cycle/213260/4 "2003-11-14T22:02:47Z")

</div>

NPR’s Talk of the Nation Science Friday Nov. 14, 2003 had a big segment about solar storm, the sun’s rotation, the 11-year cycle, and such. Here’s a link, I think. [http://www.npr.org/rundowns/rundown.php?prgId=5&prgDate=current](http://www.npr.org/rundowns/rundown.php?prgId=5&prgDate=current)

Cool stuff.