Comet ISON On Thanksgiving Day – Will We See It?

Comet ISON this morning at 9:22 a.m. CST as photographed by SOHO. In some of SOHO’s recent photo, the over-saturation spikes from blooming are missing from the comet’s head. This would indicate a drop in brightness. Credit: NASA/ESA

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!

Comet ISON entered SOHO’s close-up C2 coronagraph today. This picture was taken at 9:18 a.m. Nov. 28. Credit: NASA/ESA

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.

Comet ISON’s position is shown each hour today as it rounds the sun. Early and late in the day it will lie from 2-2.5 degrees from the sun. Times are CST. Created with Chris Marriott’s SkyMap software.

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.

Use these little pictures to help you know where Comet ISON is in relation to the sun between 8 a.m. and 2 p.m. CST Thursday Nov. 28. Add one hour for Eastern time; subtract 1 hour for Mountain and 2 hours for Pacific. Be sure to face the direction shown when using the diagrams and completely block the sun from view. Stellarium

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.

Comet ISON will be about 2.5 degrees from the sun at sunset this evening Nov. 28. Time shown is 4:30 p.m. CST.

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.

Animation using images from SOHO’s C3 coronagraph the past two days. Credit: NASA/ESA

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.

18 Responses

  1. Edward M. Boll

    I plan to look today, but I am not going to use any optical aid to increase brightness. I am afraid that I might swing the binoculars too sunward and take a chance at damaging my eyes. I may just look at the Sun with my no. 16 arc welder’s goggles today. It was 90 percent overcast here this morning, but now cleared off nicely. I do have one question. How long do you think after perihelion do you think we will find out if the comet survived?

  2. Edward M. Boll

    Kelly Beatty offers a theory why ISON seems to be fading. I hope that he is right, but for now it is just a theory.

    1. astrobob

      Let’s hope he’s right. The angle at which the sun illuminates the comet’s dust is changing as the comet moves. Beatty suggests that right now that angle is unfavorable, so the dust isn’t being illuminated as brightly as it once was. In other words, the comet’s fading is only temporary.

  3. Edward M. Boll

    100 minutes to go, the comet still has over a million miles to go toward the Sun. Normally that would include a lot of brightening now. No one is quite sure what is going on right now. The comet tracker now has it at magnitude -3.1. We should know later this afternoon how accurate the tracker is.

  4. Edward M. Boll

    One thing that I did not factor into my comet prediction was how far the comet is receding from Earth. It is receding from Earth at a faster rate that is it is going toward the Sun. Could this be a possible explanation why it does not seem to be brightening now?

    1. astrobob

      Not in the case of a sun grazer. Its intrinsic fading is the issue here. Either that or it’s phase angle-related, but it’s looking more and more like a breakup.

  5. Edward M. Boll

    If all we get out of ISON is a magnitude of -2, it will still go down as one of History’s brightest comets.

    1. astrobob

      At least within the last century, however those mags. are still tentative and of course, no one on Earth will (likey) see it that bright in the sky unlike some of the other bright comets of the last 100 years. There have also been lots of sungrazers picked up by SOHO that reached fairly bright magnitudes but were never otherwise seen.

      1. Richard Keen

        Or a tail without a cat, to paraphrase Alice.
        Very sad indeed, but in retrospect not unexpected, considering the underperformance for the past 10 months. Check Seiichi Yoshida’s light curve
        and he knocked two magnitudes off the initital predictions back in March.
        But on the plus side, “When beggars die there are no comets seen; The heavens themselves blaze forth the death of princes.” – (Mrs. Caesar in Shakespeare’s Julius Caesar)
        So princes – and their brides – can rest easy tonight.

        1. astrobob

          Nice Richard, nice. Like your humor. And yes, you’re right. Looking back, this scenario was a possibility on many observers’ minds long ago.

  6. Edward M. Boll

    I was watching the live feed on ISON for an hour now. Now, I have to walk one block away to eat Thanksgiving Dinner and chat with the folks. I plan to be back in an hour. Hopefully we know something then.

    1. astrobob

      Hopefully Edward. Enjoy your Thanksgiving! By the way, I just updated the blog with new images. Thanks again for all your observations.

  7. Norman Sanker

    Hey Bob,

    It looks like ISON is no more–fascinating, captain. The most interesting question for this layman science buff is what was the intrinsic difference between ISON and Lovejoy? Lovejoy was apparently much smaller and passed even closer to the sun but survived–at least as a headless tail. Why did ISON pfffttt so utterly? (Or has it?) Was one more dirt and the other more snow? Here’s the bright side: I won’t have to annoy my friends and acquaintances to get their butts out of bed and go stand in the cold, cold dawn. Not everyone enjoys that sort of thing. Later.

    Norman Sanker

    1. astrobob

      Good question as to their intrinsic differences. Maybe Lovejoy was larger or perhaps it held on longer and only broke up at perihelion. It appears ISON broke up days before it reached perihelion.

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