Perihelion Day. Will the comet get baked and devoured by the sun like so much turkey or will it survive? Once upon a time Comet ISON was faint, frozen and far away. Back in January, when I first saw it in the telescope, the comet seemed as tenuous as my own breath on that bitter cold night. Now it’s totally fired up and ready for a mighty right turn around the sun at the breakneck speed of over 800,000 miles per hour. Go for it ISON – we’re with you on this!
Perihelion just happens to coincide with Thanksgiving, a national holiday in the U.S., when we give thanks for the harvest and our heritage. Allow me to add a certain comet to my “what I’m thankful for” list.
Now it might be cloudy at your house today. Since you’ll want to keep up with all the action and latest photos no matter what the conditions, don’t forget to drop by the Solar Dynamics Observatory Views ISON site to see photos and movies arriving between 11:45 a.m. and noon CST.
You can also check out NASA’s Fire vs. ISON Google+ LIVE Hangout today from noon-2:30 p.m. CST where you can listen to and ask questions of professional astronomers and ace blogger Phil Plait. One of my favorite hangouts is the real-time Comet ISON distance and speed calculator where you can get a visceral sense of how insanely fast the comet’s moving.
Some of you have wondered about seeing the comet in the daytime sky. While we don’t know ISON’s exact magnitude it may be bright enough to spot in binoculars provided you completely block the sun from view. There’s even a extremely slim chance it might be visible with the naked eye in locations where the sun is high up in an exceptionally clear sky. That would be at tropical latitudes. Once ISON rounds the sun and turns north, observers in mid-northern latitudes will quickly have the edge.
If Comet ISON becomes at least as bright as Venus today (mag. -4.5) expert observers with telescopes carefully shielded so as not to allow the sun to shine into the tube stand a chance of seeing it. Early or late in the day will be the best time when the comet lies some 2.5 degrees from the sun. That’s only equal to the width of your thumb held against the sky. Don’t even bother within a few hours of perihelion. Too dangerous. Comet ISON will pass less than one solar diameter (1/2 degree) from the sun around the noon hour CST. Not only is there a good risk of burning holes in your retinas, but the glare so close to the sun will almost certainly mask the comet from view.
In a spirit of optimism then, I offer these maps. The first shows ISON’s hour to hour position to scale. Although the comet will be brightest today, it will never lie more than 2.5 degrees from the sun as seen from the western hemisphere. I’ve seen Venus in my telescope at that distance, but it was a tricky proposition, and I had to exercise extreme care to keep direct sunlight out of the eyepiece and my eye. Telescope observers have also used red and polarizing filters to help reduce glare and increase contrast for near-sun viewing of comets and planets.
If plan to attempt an observation with binoculars or naked eye, you’ll need three things: an extremely clear, haze-free sky and something to block the sun from view. I’ve used power poles, church steeples, rooftops, buildings, street lights and even clouds to hide the sun. Whatever you do, NEVER stare directly at the sun especially when using binoculars.
Cover the sun completely, and if you see bright glare returning to the field of view, change your position slightly to hide the sun again. Earth rotates causing the sun’s position constantly change. You have to be on your toes to keep it from shining into your eyes.
So what’s the third thing? Pure luck and cooperation from ISON. I have to say that today I’m not as optimistic about daylight observations. I expected the comet to become much brighter overnight based on how quickly it had brightened in the previous 24 hours. Unfortunately that didn’t happen. At the moment ISON appears to have faded judging by a lack of spikes around its head. It may only be around magnitude 0 now (10 a.m. CST) however this condition may be temporary and have to do with the angle at which sunlight illuminates the comet’s dust. This angle will change throughout the day and ISON may re-brighten.
The tail also reminds me of Comet Lovejoy in 2011 when its nucleus broke up and created a bright tail but very faint head. We won’t know exactly what ISON’s going through until it rounds the sun and comes out the other side.