Comet ISON snapped to life after the Nov. 14 outburst, but now appears to be waning a bit. I saw its remarkable transformation from a so-so comet on Nov. 13 to one with some real punch two mornings later. By the 15th, the coma or head doubled in size and ISON’s tail shot out over 8 degrees – the distance your fist spans when held at arm’s length against the sky.
Then everything stopped. More recent reports from Sunday and today show that the comet has faded some since the outburst, dropping from magnitude 5 to about 6. That’s a difference in brightness of 2 to 2 1/2 times. The tail has thinned as well.
In astronomy, the lower the magnitude number, the brighter the object, so this is not welcome news. A break or crack in ISON’s crust that exposed fresh ice to the sun’s heat was the likely cause of the recent outburst; while it’s almost certain to happen again, no one can predict when.
Couple the slight fade with low altitude, dawn light and bright moonlight and it’s no wonder even some seasoned amateur astronomers are having difficulty finding ISON in binoculars.
The good news is that the comet’s central core or nucleus still appears to be intact. We don’t want it to bust apart – not this soon anyway – or we’d be in for a poor show after perihelion (closest approach to the sun) on the 28th. Should the nucleus break up during or shortly after perihelion, the ice chunks would vaporize like crazy and create a spectacular tail with a small or even absent head.
There’s been discussion on the Comet ISON Observing Campaign website among some astronomers that the two wings of material now flaring inside the comet’s coma or head might be due to the breakup of the nucleus, but the jury’s still out.
If the comet survives the intense 5000 degree solar roasting coming its way at perihelion, it should become showy enough to put a smile on the faces of those willing to stand out at dawn in December. In the meantime, you can use the maps from this blog to still track it yourself, or you can catch up on your sleep and wait until it enters the field of view of the Solar and Heliospheric Observatory (SOHO).
SOHO observes and photographs the sun 24/7 from a vantage point 1 million miles from Earth toward the sun. Onboard it has two of the coolest tools in the world for watching sungrazing comets like ISON. Called coronagraphs, they block or occult the sun’s brilliant disk making it possible for astronomers and regular types like you and me to study the sky near the sun.
Comet ISON enters the field of view of SOHO’s wide-field coronagraph early on Nov. 27 and departs late on the 30th. The comet should brighten dramatically during this time, so be sure to watch for it at this link. I’ll have continued ISON updates as developments warrant, so please stop by anytime. Questions? Just drop us a comment below.