[meteorite-list] COMET McNAUGHT IS STILL VISIBLE IN DAYLIGHT!

From: MexicoDoug <MexicoDoug_at_meteoritecentral.com>
Date: Thu, 18 Jan 2007 18:52:04 -0600
Message-ID: <001001c73b64$27cf1680$d7cd5ec8_at_0019110394>

Steve wrote:

"Also, for seeing Comet McNaught after the sun goes down here in AZ I don't think is possible as it sets before the sun and the tail points downward and toward the south. So it is a daylight object for us here in the US and the north."

Hello again Steve, and thanks for the wonderful posts from someone as enthusiastic and luckily located for this incredible event for those that careful to observe it, which is of the type of once or twice in most lifetimes. Let me ditto all of your accolades to the show, though I have had a rather poor latitude and sky quality for such remarkable observations.

I do differ on the first quoted statement you made which is of meteoroidic interest. I think this case we have is the case to watch, and gives us a unique experience to detect the exceptions to the general rule of "the comet's tail always points away from the Sun."

First, you need to consider you are looking at a projection when you observe - essentially a two dimensional figure, while the tail points "away" in the third dimension in a way very difficult to properly view.

As you sure are aware, comets have two qualities of tails which can point in different directions. Near the nucleus and coma with the instantaneous production of dust material and charged particles, they converge in the same direction: the anti-solar direction as you mention. However, this comet has at least a 20 million km long tail and is very close to perihelion which was correspondingly near the ecliptic, as it continues to dip south while the tails are extended relatively parallel to the ecliptic (might say "west" if you were using Solar centered coordinates), though this of course is rapidly changing to "south", too.

The detail occurs in that while the ion trail is picked up by the Solar "wind" and follows this anti-solar orientation (from flat to directly below the plane of the Solar system which is the basic direction of travel of the comet, too, the brilliant dust trail in such an exciting case as this one has managed to pick up a great deal of curvature as things are happening so fast. Material that was sloughed off previous to crossing the Solar plane is in its own Unique stream, something like a meteoroid stream will diffuse along the whole orbit.

Projections are pretty tricky, but remember the comet is 130 million km away or so, and just because it crosses the plane of Earth's orbit, does create an instant flip. Look at some of the beautiful pictures of the tail and you can see all the physics at work of both of our comments.

The bottom line is that the tails can easily delay a little to reorient, as the great curvature in this case demonstrates, and we need to view this from a neutral detached point, not from an overly geo-centric perspective which would be misleading.

Maybe this can help clear up my thinking? Note the tails' orientations:
http://spaceguard.esa.int/NScience/neo/neo-what/com-tail.htm

Anyhow that is what I think, right or wrong, plus there also were unverified observations this phenomenon, and you are in Flagstaff, where I wish I could be to check this out. But this is a transient effect and will quickly be lost if it hasn't been already. Just, specifically, the reason you suggested it is not possible, is the reason that makes it so interesting and exciting to look for after Sunset.

My two centavos and a wish for best health,
Doug



  ----- Original Message -----
  From: Steve Schoner
  To: MexicoDoug at aim.com ; meteorite-list at meteoritecentral.com
  Sent: Thursday, January 18, 2007 3:20 PM
  Subject: Re: [meteorite-list] COMET McNAUGHT IS STILL VISIBLE IN DAYLIGHT!


  MexicoDoug and all.

  I can still see it with the naked eye! The sky is crystal blue today. It is just below and somewhat left of the the sun about 9 degrees or so.

  Venus can also be spotted to the east about 5 fist lengths away (40 to 50 degrees?) away from the sun. But it is hard to tell the distance in daylight. (I should have made a graduated cross-bow for daylight observations to ascertain the scale)

  The comet head is just about as bright as Venus maybe more. If one really looks at it you might just get a trace of the tail. As for the magnitude of Venus at this time (-2.x?) I will have to look it up on star charts to find out for this date.

  Also, for seeing Comet McNaught after the sun goes down here in AZ I don't think is possible as it sets before the sun and the tail points downward and toward the south. So it is a daylight object for us here in the US and the north.

  What is amazing about my observations over from the 15th to today, the 18th, is that it has moved so fast! I can actually trace its orbit around the sun over these days.

  It's great to live in Flagstaff with the clear sky (when it is not snowing as it did on the 12th to the 14th, the best days to have seen this daylight comet.)

  But I am extremely happy to have seen this event. I missed Ikeya Seki as it zipped around the sun, simply because no one told me how to look for it. My friends that actually saw it, saw it by accident when they were walking in the shade. The tail was 2 or more degrees long and tightly curved as Ikeya Seki zipped around the sun at 500,000 mph! Within the course of an hour or so it was out of sight during the day.

  It was an event in my life that I lamented to have missed every-time I thought on it. The Great Leonid display of 1966 too, having been washed out for that very night and that night alone with a thunderstorm.

  But seeing this comet in broad daylight, and moving in its orbit over the course of 4 days is very satisfying indeed.

  Steve Schoner

  IMCA #4470

  -- "MexicoDoug" <MexicoDoug at aim.com> wrote:
  "This brings up a question to all. Did anyone down south of the equator see
  this [comet] in broad daylight from 01/12 to 01/16? All the reports I have
  thus far seen are from the north. It should have been easily seen in broad
  daylight down there as the sun would be higher in a blue sky."

  Hello Steve,

  Please correct me if I've not understood your statement but, this is not
  appreciably true. Lets say you have in 2 km elevation Flagstaff a view with
  the Sun at 33? high in the sky (only one third above the horizon=0? to the
  zenith=90?). And lets compare that to a location down south near the tropic
  of Capricorn (where the Sun is at a neckbreaking 88? altitude, basically at
  the zenith). Call that place Rio's Ipanema Beach, at sea level.

  Both locations have a similar loss of magnitude, just about 0.3. Actually
  Flagstaff is a little better off by a few percent. So in both places, the
  comet would appear to be -4.7 magnitude instead of the true e.g., -5.0, from
  sitting on top of the atmosphere like Hubble. The point is, with something
  this bright, the difference is much more sensitive to other things and you
  have minimal loss. Even if the comet were at the exact zenith and you were
  2,000 meters above Rio, you would still lose 0.2 magnitudes - after all you
  can only do so well from the soup we live in and it is a light contaminated,
  polluted muck once you are outside the fishbowl looking in...

  The moral of this is that few people in Arizona (well, Phoenix probably
  realizes the way it was) and New Mexico know just how uniquely lucky they
  are. When we start to factor seeing, dust and humidity into the equation
  you guys are basically on the top of the world as you have an especially
  cooperative airmass on top of you. Plus, I suspect that the greater
  magnitude of the Sun in a zenith situation - takes its toll on contrast with
  our poor eyes as well making it at best a wash.

  Btw, plenty of folks saw it in the Southern Hemisphere during the day and
  twilight, though everyone had to put up with the same 5-7? angular
  separation from the Sun from our little Blue Spaceship Dot, the comet being
  120 million kilometers away. The tail has improved somewhat apparently.
  (Thus - Arizona highlands was just about the finest place to be, all things
  considered). It apparently gave the Ozies quite a show in Perth last
  evening - like you northerners had. But the Northern hemisphere really got
  first dibs on this comet. Did you know if you were in Barrow, Alaska you
  could have watched the comet rise and set from about 9 am to 5 pm every day
  for the first two weeks of January - and even had to worry about the Sun,
  because it won't be rising there until say, January 23. Might be a wee bit
  nippy, but I think that the coinciding of a comet rising and setting instead
  of the Sun is the stuff of legends that turn men's bones into stones...And,
  we're meteorite hunters (I read Gallant's book, too and am a little hyper),
  the (-) 26? below zero FAHRENHEIT (-32?C) right now would be good practice
  for Antarctica, or maybe even Dave's Wyoming... It got up to -14?F (-26?C)
  yesterday in Barrow which was typical for the high-noon comet a few days
  earlier.

  Good health,
  Doug
  PS, you can still see the Comet's tail after Sunset from your skies - hope
  you check this out. Did you know the Comet is the largest object in the
  Solar System at the moment, a mere 10-20 million kilometers long and with a
  tail wider than the Sun?


  From: "Steve Schoner" <schoner at mybluelight.com>
  To: <schoner at mybluelight.com>
  Cc: <meteorite-list at meteoritecentral.com>
  Sent: Wednesday, January 17, 2007 9:32 AM
  Subject: Re: [meteorite-list] COMET McNAUGHT IS STILL VISIBLE IN DAYLIGHT!


  Hello all,

  Don't know why my report of my last daylight sighting of this comet
  (01/16/07) did not go through, so I post again. I was very impressed to
  have spotted it yesterday in Flagstaff's clear blue skies, and I had
  some of my co-workers come out and confirm my sightings. They were
  just as amazed as me to have seen it. I also pointed out Venus well to
  the left and up above it which they also spotted as well. They were
  amazed that I pointed it out as they had no idea that one could
  actually see a planet in broad daylight.

  In regards to Comet McNaught the "forward scatter" is rapidly vanishing
  and it is very unlikely that it will be seen today by anyone in broad
  daylight (unless you are on a very high mountain with very clear
  skies). I will give it my last try this afternoon. If I can't see it
  with my naked eyes, I won't try with binoculars as it is too dangerous
  to look anywhere near the sun.

  This brings up a question to all. Did anyone down south of the equator
  see this in broad daylight from 01/12 to 01/16?

  All the reports I have thus far seen are from the north. It should
  have been easily seen in broad daylight down there as the sun would be
  higher in a blue sky.

  Steve Schoner
  IMCA #4470
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://six.pairlist.net/pipermail/meteorite-list/attachments/20070118/9013adb2/attachment.html>
Received on Thu 18 Jan 2007 07:52:04 PM PST