Looks like Comet ISON is finally rubbing the sleep from its eyes. In the past 24 hours the comet has brightened significantly, rising from magnitude 7.5-80 (visible faintly in binoculars) all the way up to 5.5 or brighter than the naked eye limit. That means that despite its rapidly dropping altitude and the moon returning to the morning sky, it should become easier to see. A couple of observers have already spotted it faintly with their bare eyeballs.
Amateur astronomers report that ISON’s head or coma has become more compact and condensed; the tail has evolved from a single plume-like streak to a complicated tangle of picturesque streamers. Astronomer Emmauel Jehin, a member of the European TRAPPIST (TRAnsiting Planets and Planetesimals Small Telescope) team, shares two pieces of good news. His observations with the group’s 23.6-inch (60-cm) telescope have detected a tenfold increase in dust blasting from the comet’s nucleus as well as additional jet of icy and dust in the past 48 hours. No question about it, an outburst is underway.
Peering deep into ISON’s coma, Jehin noted that the innermost nuclear region (the small, bright, fuzzy center of the comet) is still intact with no signs of a breakup. So far, so good. ISON’s holding together nicely on its inbound journey. If it keeps it up, we may see a fine comet indeed after perihelion on Nov. 28.
Funny thing – I was out watching ISON on Tuesday with students in my community ed astronomy class at the beginning of the outburst. While the coma’s core glowed brighter compared to a couple days earlier the full effects of the transition had only begun.
It should come as no surprise that ISON’s leaping to life. Today it’s just under 60 million miles from the sun. The closer the comet gets, the more intense solar heating becomes. Heat vaporizes the comet’s dust-laden ice, and sunlight blows the material back to form a tail.
The sudden brightness jump could very well be from new cracks or fissures developing in icy crust. Exposed to the sun’s heat for the first time, gobs of ice rapidly vaporize and can cause the coma to brighten dramatically.
I’ve included a couple maps to help you find ISON. It’s in Virgo very low in the southeastern sky just before the start of dawn. Be sure you pick a spot that’s open in that direction. Watch for it beginning about 2 hours before sunrise. At dawn’s first blush, the comet is currently between 15-20 degrees high.