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General Astronomy >> General Observing and Astronomy

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starcrafter
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ISON Aftermath
      #6037291 - 08/20/13 08:49 PM

I just had a passing thought about the ISON comet. I've heard that the comet's brightness is progressing far worse than people had been hoping for, and that it might well end up being a dud.

But, I remember a month or two ago reading a story about how much dust was melting off the thing (I don't recall a specific amount, only thinking that the sum total seemed enormous). So, even if ISON turns out to be a bit of a stinker visually, wouldn't that huge amount of debris turn into a nice meteor shower?


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kfiscus
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Re: ISON Aftermath new [Re: starcrafter]
      #6037311 - 08/20/13 09:18 PM

Only if our orbit crosses its orbit. I don't recall anyone saying that this is the case.

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AstroTatDad
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Re: ISON Aftermath new [Re: kfiscus]
      #6037376 - 08/20/13 10:08 PM

I still think we will get a good show, ISON's nucleus seems to be small from what was gathered. And if that is the case it will be a slow rise in brightness, we are still a good few months away from it will be 730,000 miles near the Sun. The hype I think they were giving was kind of a jumping the gun statement in my opinion, comets are very unpredictable know one knows what is going to happen. The sun might eat it right up on its pass by then sun... lol joking!! I hope it's a good and safe show, it will be cool to see.

Here is some added info from stuff I have saved from researching comets.

What happens to a comet when it gets near the sun?
As a comet approaches the sun, it grows warmer and some of the ices heat up and become gas (sublimating), releasing the dust grains that were trapped in the ice. This dusty gas coming from the nucleus is heated by the sun and forms a glowing hot cloud around the comet called the coma. Even though the nucleus might only be a couple of kilometers across, the cloud (or coma) can grow significantly (up to 100,000 kilometers across) during perihelion (its closest point to the sun). Comets also develop dust and gas tails.

Comets are usually seen only in the night sky. How is it that we see the effect of the sunís light on a comet, after the sun has set? (Hint: what makes the moon shine?)

Comets are visible at night because the sunís light is shining on them, just as the moon can be illuminated in the night sky - even though the part of the Earth that we are on has rotated away from the sun and is in the dark (as the earth spins on its axis). Furthermore, it is important to think about the earth and the comet, and their relative positions to each other as they orbit the sun. Also, the comet we see may be on the far side of the sun from the earth, and thus visible at early evening or early morning.

A comet can lose hundreds, or even thousands of kilograms of material each second as it passes by the sun and forms a dust tail. Does this mean that comets could eventually disappear? What do you think, and why?

Yes. Eventually (it may take millions of years) comets will loose all of their material through sublimation from passing near the sun during perihelion and disappear. It is also possible that a comet will get trapped in the gravitational pull of a large planet like Jupiter or the sun and breakup or smash into the surface with a tremendous impact like Comet Shoemaker-Levy in 1994 or Comet LINEAR in 2000.


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Kevdog
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Re: ISON Aftermath new [Re: kfiscus]
      #6037378 - 08/20/13 10:13 PM

If you search for the posts about ISON you can find the java program that shows the orbit of ISON. It definitely crosses earth's orbit and based on the program we should go through where the cloud of dust was in December sometime.

So we should get at least some sort of new meteor shower in December.


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AstroTatDad
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Re: ISON Aftermath new [Re: Kevdog]
      #6037396 - 08/20/13 10:28 PM

Quote:

If you search for the posts about ISON you can find the java program that shows the orbit of ISON. It definitely crosses earth's orbit and based on the program we should go through where the cloud of dust was in December sometime.

So we should get at least some sort of new meteor shower in December.




Here lets add some more hype. ISON meteor shower coming this December "the biggest show ever seen" lol.
But really I'm sure it will not dud out on us and most likely will get some showers as earth passes the dust trails. Guess we will have to see, at least we got to see a new Nova to hold us off for a bit.


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kfiscus
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Re: ISON Aftermath new [Re: Kevdog]
      #6037468 - 08/20/13 11:10 PM

Thank you for correcting my mis-remembering.

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BrooksObs
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Reged: 12/08/12

Re: ISON Aftermath new [Re: Kevdog]
      #6037484 - 08/20/13 11:23 PM

Quote:

If you search for the posts about ISON you can find the java program that shows the orbit of ISON. It definitely crosses earth's orbit and based on the program we should go through where the cloud of dust was in December sometime.

So we should get at least some sort of new meteor shower in December.




The orbits of the Earth and Comet ISON do not intersect, or actually cross. The closest approach of the comet's orbit to that of the Earth's amounts to a several million mile separation on the in-bound leg of the comet's orbit.

Meteor showers from known comets can only be anticipated when the the separation between the two orbits is only a tiny fraction of the distance between the two in question.

Thus, ABSOLUTELY NO METEOR SHOWER CAN BE ANTICIPATED FROM COMET ISON IN DECEMBER.

BrooksObs


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GlennLeDrew
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Re: ISON Aftermath new [Re: BrooksObs]
      #6037534 - 08/21/13 12:08 AM

Furthermore, a one-time pass of such a comet has all its dust moving along with it, and in close proximity. That is, the larger particles which are not so rapidly acellarated to form the tail, pointing generally away from the Sun. And so we could only have a meteor shower if the comet itself passed *very* close to Earth.

The 'classic' meteor showers, which occur annually, result from the dispersal of dust along the orbit over a *great* many orbits of the comet. Like the comet nucleus, the particles are in orbit too. Comets do not lay down a carpet or stream of dust particles that just stay in place. The particles share basically the same orbit as the nucleus, some slightly advancing and others slowly trailing on the orbit, it taking some number of orbits for the dispersion to amount to any significant distance along the orbit.


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AstroTatDad
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Re: ISON Aftermath new [Re: BrooksObs]
      #6037550 - 08/21/13 12:45 AM

I was actually trying to be humorous by my statement of "December" sorry about the misleading informative information and my lack of trying to be funny. But yeah... Maybe something more like Mid January for a shower, hey anything is possible

Anyhow,
ISON is shedding around 120,000 pounds of dust per minute as we speak, and from the looks of it's path around the "sun" comet ISON will pass both sides of earth "not close to earth" on its journey around the sun. The dust it leaves behind will be pushed outward by the solar wind, and it is possible that Earth will encounter this dust and pass through the cloud of dust left from comet ISON, and we "might" see a shower that could last for several days. We probably will just encounter fine dusty's maybe nothing big like the meteor showers we have all viewed in the pass. It's also possible there will be noctilucent clouds above the earth's surface. Again these are all possibilities know one really knows what is going to happen. It's all unprecedented, so I guess for better way of putting it is, lets see what happens.


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GlennLeDrew
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Re: ISON Aftermath new [Re: AstroTatDad]
      #6037557 - 08/21/13 12:52 AM

Hardly unprecedented. In the 1910 passage of Halley's Comet, the Earth probably did pass through the gas tail. I recall no reports of enhanced meteor activity as a result; we were presumably too far from the just-released dust.

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AstroTatDad
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Re: ISON Aftermath new [Re: GlennLeDrew]
      #6037581 - 08/21/13 01:18 AM

Has comet ISON gave us such a pass that it's going to encounter on its journey around the sun? Or I'm I missing something here, because I would like to know. That is why i stated "unprecedented" sorry... I have only been interested in comets and what they are about just in this last year. So I'm fairly new to learning about comets, so I only know what I have read. I don't have a degree or anything, so I'm more of a self learner from personal experience or information that has been shared with me from others.
I like learning, and having the correct information in my mind so if I state something that can be wrong I'm thankfully from others correcting me with more knowledge then me.


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Kevdog
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Re: ISON Aftermath new [Re: BrooksObs]
      #6038440 - 08/21/13 02:19 PM

Sometimes it's easy to forget the scale of things.

Here's the orbits in the program:


It looked pretty close when I first viewed it, but after looking closer it is quite a separation. Too bad the program doesn't have a measure function! This is where the comet it closest to earth's orbit.

So on Jan 16th we pass the closest we get to ISON's orbit. I was hopeful that we'd be close enough to pick up some of the dust and get another show besides just the comet. Ah well!


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karstenkoch
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Reged: 04/21/12

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Re: ISON Aftermath new [Re: GlennLeDrew]
      #6038852 - 08/21/13 06:02 PM

Quote:

Like the comet nucleus, the particles are in orbit too. Comets do not lay down a carpet or stream of dust particles that just stay in place. The particles share basically the same orbit as the nucleus...




Glenn,
I've been wondering about this. Now it seems obvious! Thank you. This also would appear to contribute to the direction of the radiant, the spot in the sky where the meteors come from.


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AstroTatDad
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Re: ISON Aftermath new [Re: karstenkoch]
      #6038927 - 08/21/13 06:42 PM

I tried to find the page I read all this stuff from a while back, but this is close as I could find.

Veteran meteor researcher Paul Wiegert of the University of Western Ontario has been using a computer to model the trajectory of dust ejected by Comet ISON, and his findings suggest that an unusual meteor shower could be in the offing.

"For several days around January 12, 2014, Earth will pass through a stream of fine-grained debris from Comet ISON," says Wiegert. "The resulting shower could have some interesting properties.

According to Wiegert's computer models, the debris stream is populated with extremely tiny grains of dust, no more than a few microns wide, pushed toward Earth by the gentle radiation pressure of the sun. They will be hitting at a speed of 56 km/s or 125,000 mph. Because the particles are so small, Earthís upper atmosphere will rapidly slow them to a stop.
"Instead of burning up in a flash of light, they will drift gently down to the Earth below," he says.
Donít expect to notice. The invisible rain of comet dust, if it occurs, would be very slow. It can take months or even years for fine dust to settle out of the high atmosphere.

While the dust is ďup there,Ē it could produce noctilucent clouds (NLCs).

Paul Wiegert's model of the Comet ISON debris stream: AVI movie
NLCs are icy clouds that glow electric-blue as they float more than 80 km above Earth's poles. Recent data from NASA's AIM spacecraft suggests that NLCs are seeded by space dust. Tiny meteoroids act as nucleating points where water molecules gather; the resulting ice crystals assemble into clouds at the edge of space itself.
This is still speculative, but Comet ISON could provide the seeds for a noctilucent display. Electric-blue ripples over Earth's polar regions might be the only visible sign that a shower is underway.

Wiegert notes another curiosity: "The shower is going to hit our planet from two directions at once."

When Earth passes through the debris stream, we will encounter two populations of comet dust. One swarm of dust will be following the Comet ISON into the sun. Another swarm will be moving in the opposite direction, pushed away from the sun by solar radiation pressure. The streams will pepper opposite sides of Earth simultaneously.

"In my experience, this kind of double whammy is unprecedented," says Wiegert.

Bill Cooke, lead scientist at NASA's Meteoroid Environment Office, says there's little danger to Earth-orbiting spacecraft. "These particles are just too small to penetrate the walls of our satellites, and they don't stand a chance against the heavy shielding of the ISS." However, he adds, mission operators will be alert around January 12th for possible anomalies.

Link here: http://science.nasa.gov/science-news/science-at-nasa/2013/19apr_isonids/


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Tony Flanders
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Re: ISON Aftermath new [Re: karstenkoch]
      #6038979 - 08/21/13 07:03 PM

Quote:

Quote:

Like the comet nucleus, the particles are in orbit too. Comets do not lay down a carpet or stream of dust particles that just stay in place. The particles share basically the same orbit as the nucleus...




Glenn,
I've been wondering about this. Now it seems obvious! Thank you. This also would appear to contribute to the direction of the radiant, the spot in the sky where the meteors come from.




Indeed it is; it's the dominant effect. If meteoroids just hung there in space, they would all hit Earth's leading edge, meaning that the radiant of all showers would be highest at dawn.

But in fact, meteoroids, being in elliptical orbits like their parent comets, have essentially "fallen" from much farther from the Sun by the time they reach Earth's orbit. That means they're moving much faster than Earth is. Some, like the Perseids, do indeed hit Earth almost head-on. Others, like the Geminids, catch up from behind.


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GlennLeDrew
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Re: ISON Aftermath new [Re: Tony Flanders]
      #6039218 - 08/21/13 09:41 PM

Jeff,
That short article is vague on a number or points, which is a real problem with press releases composed for public consumption. About the 'double streams' of dust... Reading almost between the lines (which can only be done with some level of knowledge Joe Public mostly does not possess), the two streams comprise *very* different particle sizes, the range being greater than one might imagine. The stream moving with the comet contains particles which would cause bright meteors if intercepted by an atmosphere.

The other stream is essentially the dust tail, whose particles are so small they are rapidly accelerated by the solar wind, extending fairly quickly to distances of order an astronomical unit from the nucleus. As noted in the article, these particles are so minute that they are decelerated far too high up in the atmosphere to result in meteors. And as not stated, the stream of very small particles can in this instance only reach us because of the great distance they are blown by the solar wind.

That they will not result in visible meteors makes me wonder how this would be of *general* interest (to those who do not watch the sky.) Such information, without the clearest caveats, can all too easily give the impression of a meteor shower if read hastily.


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AstroTatDad
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Re: ISON Aftermath new [Re: GlennLeDrew]
      #6039230 - 08/21/13 09:50 PM

Thanks Glenn.

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Kevdog
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Re: ISON Aftermath new [Re: GlennLeDrew]
      #6040454 - 08/22/13 04:43 PM

So it both confirms and denies what I was thinking.

Yes, we will pass through some of the tail of the comet. It is "close enough" to get some of the dust of the comet in January.

No, the particles we will hit are not big enough to give a meteor shower.

Fun stuff!


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