As with the &lt;a href="9/11"&gt;9/11&lt;/a&gt; disaster discussed above, cycles attach themselves to celebrities or national catastrophes such as the death of Diana, Princess of Wales, the death of Michael Jackson, and the Space Shuttle Challenger disaster. These cycles arise regularly as a response to terrible unexpected events which command the national news. An in-depth analysis of the Challenger joke cycle documents a change in the type of humour circulated following the disaster, from February to March 1986. "It shows that the jokes appeared in distinct 'waves', the first responding to the disaster with clever wordplay and the second playing with grim and troubling images associated with the event…The primary social function of disaster jokes appears to be to provide closure to an event that provoked communal grieving, by signaling that it was time to move on and pay attention to more immediate concerns".