Why did Comet Holmes flare up?
Yet Comet Holmes has brightened up unexpectedly on a previous occasion: that of November 1892 led to its discovery by E. Holmes in England. It was subsequently determined to be a periodic comet, with a revolutionary period of about every seven years. You can see its orbit in relation to other planets courtesy of Larry’s animation here. Much less, though, has been made of the fact of where it was when the current flare-up occurred. The Armagh Observatory’s website puts the comet at some 230m miles from the Sun – a distance from, and quite a long time after, its closest point to the Sun, which occurred on May 4, 2007. In the accepted view, comets are thought to comprise rocky and icy solids in a mixture termed “rocky snowballs” by some and “icy rockballs” by others. They get brighter and sprout tails as the “icy” component is thought to sublimate from solid to gaseous state under the influence of solar heating, which typically begins affecting them at a point just inside the orbit of Jup
